Carlos Marques publications can be found here
Citations from Google Scholar Citations.
CNRS Senior Scientist, MCube Group Leader
Carlos Marques publications can be found here
Citations from Google Scholar Citations.
| Micheletto, Y. M. S., Marques, C. M., da Silveira, N. P., & Schroder, A. P. (2016). Electroformation of Giant Unilamellar Vesicles: Investigating Vesicle Fusion versus Bulge Merging. Langmuir, 32(32), 8123–8130.|
Abstract: Partially ordered stacks of phospholipid bilayers on.a flat substrate can be obtained by the evaporation of a spread droplet of phospholipid-in-chloroform solution. When exposed to an aqueous buffer, numerous micrometric buds populate the bilayers, grow in size over minutes, and eventually detach, forming-the so-called liposomes or vesicles. While observation of vesicle growth from a hydrated lipid film under an optical microscope suggests numerous events of vesicle fusion, there is little experimental evidence for discriminating between merging of connected buds, i.e., a shape transformation that does not imply bilayer fusion and real membrane fusion. Here, we use electroformation to grow giant unilamellar vesicles (GUVs) from a stack of lipids in a buffer containing either (i) nanometric liposomes or (ii) previously prepared GUVs. By combining different fluorescent labels of the lipids in the substrate and in the solution, and by performing a fluorescence analysis of the resulting GUVs, we clearly demonstrate that merging of bulges is the essential pathway for vesicle growth in electroformation.
| Micheletto, Y. M. S., Marques, C. M., Silveira, N. P. da, & Schroder, A. P. (2016). Electroformation of Giant Unilamellar Vesicles: Investigating Vesicle Fusion versus Bulge Merging. Langmuir, 32(32), 8123–8130.|
Abstract: Partially ordered stacks of phospholipid bilayers on a flat substrate can be obtained by the evaporation of a spread droplet of phospholipid-in-chloroform solution. When exposed to an aqueous buffer, numerous micrometric buds populate the bilayers, grow in size over minutes, and eventually detach, forming the so-called liposomes or vesicles. While observation of vesicle growth from a hydrated lipid film under an optical microscope suggests numerous events of vesicle fusion, there is little experimental evidence for discriminating between merging of connected buds, i.e., a shape transformation that does not imply bilayer fusion and real membrane fusion. Here, we use electroformation to grow giant unilamellar vesicles (GUVs) from a stack of lipids in a buffer containing either (i) nanometric liposomes or (ii) previously prepared GUVs. By combining different fluorescent labels of the lipids in the substrate and in the solution, and by performing a fluorescence analysis of the resulting GUVs, we clearly demonstrate that merging of bulges is the essential pathway for vesicle growth in electroformation.
| Micheletto, Y. M. S., Moro, C. F., Lopes, F. C., Ligabue-Braun, R., Martinelli, A. H. S., Marques, C. M., et al. (2016). Interaction of jack bean (Canavalia ensiformis) urease and a derived peptide with lipid vesicles. Colloids Surf B Biointerfaces, 145, 576–585.|
Abstract: Ureases are metalloenzymes that catalyze the hydrolysis of urea to ammonia and carbon dioxide. Jack bean (Canavalia ensiformis) produces three isoforms of urease (Canatoxin, JBU and JBURE-II). Canatoxin and JBU display several biological properties independent of their ureolytic activity, such as neurotoxicity, exocytosis-inducing and pro-inflammatory effects, blood platelets activation, insecticidal and antifungal activities. The Canatoxin entomotoxic activity is mostly due to an internal peptide, named pepcanatox, released upon the hydrolysis of the protein by insect cathepsin-like digestive enzymes. Based on pepcanatox sequence, Jaburetox-2Ec was produced in Escherichia coli. JBU and its peptides were shown to permeabilize membranes through an ion channel-based mechanism. Here we studied the JBU and Jaburetox-2Ec interaction with platelet-like multilamellar liposomes (PML) using Dynamic Light Scattering and Small Angle X-ray Scattering techniques. We also analyzed the interaction of JBU with giant unilamellar vesicles (GUVs) using Fluorescence Microscopy. The interaction of vesicles with JBU led to a slight reduction of hydrodynamic radius, and caused an increase in the lamellar repeat distance of PML, suggesting a membrane disordering effect. In contrast, Jaburetox-2Ec decreased the lamellar repeat distance of PML membranes, while also diminishing their hydrodynamic radius. Fluorescence microscopy showed that the interaction of GUVs with JBU caused membrane perturbation with formation of tethers. In conclusion, JBU can interact with PML, probably by inserting its Jaburetox “domain” into the PML external membrane. Additionally, the interaction of Jaburetox-2Ec affects the vesicle's internal bilayers and hence causes more drastic changes in the PML membrane organization in comparison with JBU.
Keywords: Jaburetox-2Ec; Jack bean urease; Light scattering; Liposomes; Saxs
| Aoki, P. H. B., Schroder, A. P., Constantino, C. J. L., & Marques, C. M. (2015). Bioadhesive giant vesicles for monitoring hydroperoxidation in lipid membranes. Soft Matter, 11(30), 5995–5998.|
Abstract: Osmotic stresses, protein insertion or lipid oxidation lead to area increase of self-assembled lipid membranes. However, methods to measure membrane expansion are scarce. Challenged by recent progress on the control of phospholipid hydroperoxidation, we introduce a method to quantitatively evaluate membrane area increase based on the bio-adhesion of Giant Unilamellar Vesicles.
| Bauer, M., Kekicheff, P., Iss, J., Fajolles, C., Charitat, T., Daillant, J., et al. (2015). Sliding tethered ligands add topological interactions to the toolbox of ligand-receptor design. Nature Communications, 6.|
Abstract: Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand-receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand-receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering.
| Korobko, A. V., Marques, C. M., Schoeps, M., Schaelder, V., Wiesner, U., & Mendes, E. (2015). Dielectric discontinuity in equilibrium block copolymer micelles. Soft Matter, 11(36), 7081–7085.|
Abstract: The surface tension between the hydrophobic core and the solvent is known to play a major role in the self-assembly of diblock copolymer micelles in solution. Coulombic forces are also very important in the case of aggregates with weakly charged coronas. The aggregation number and morphology are often tuned by the addition of electrolytes to the solution via electrostatic screening and an eventual change in solvent quality. However, when the surface tension is low enough, dielectric discontinuity between the core and the solvent becomes important enough in comparison to other mechanisms, driving the surface tension at the same time it screens electrostatic interactions in the corona. Below, we demonstrate the importance of this effect for micelles with neutral and weakly charged coronas.
| Mukherji, D., Marques, C. M., Stuehn, T., & Kremer, K. (2015). Co-non-solvency: Mean-field polymer theory does not describe polymer collapse transition in a mixture of two competing good solvents. Journal of Chemical Physics, 142(11).|
Abstract: Smart polymers are a modern class of polymeric materials that often exhibit unpredictable behavior in mixtures of solvents. One such phenomenon is co-non-solvency. Co-non-solvency occurs when two (perfectly) miscible and competing good solvents, for a given polymer, are mixed together. As a result, the same polymer collapses into a compact globule within intermediate mixing ratios. More interestingly, polymer collapses when the solvent quality remains good and even gets increasingly better by the addition of the better cosolvent. This is a puzzling phenomenon that is driven by strong local concentration fluctuations. Because of the discrete particle based nature of the interactions, Flory-Huggins type mean field arguments become unsuitable. In this work, we extend the analysis of the co-non-solvency effect presented earlier [D. Mukherji et al., Nat. Commun. 5, 4882 (2014)]. We explain why co-non-solvency is a generic phenomenon, which can only be understood by the thermodynamic treatment of the competitive displacement of (co) solvent components. This competition can result in a polymer collapse upon improvement of the solvent quality. Specific chemical details are not required to understand these complex conformational transitions. Therefore, a broad range of polymers are expected to exhibit similar reentrant coil-globule-coil transitions in competing good solvents. (C) 2015 AIP Publishing LLC.
| Weinberger, A., Tanasescu, R., Stefaniu, C., Fedotenko, I. A., Favarger, F., Ishikawa, T., et al. (2015). Bilayer Properties of 1,3-Diamidophospholipids. Langmuir, 31(6), 1879–1884.|
Abstract: A series of 1,3-diamido phosphocholines was synthesized, and their potential to form stable bilayers was investigated. Large and giant unilamellar vesicles produced from these new lipids form a wide variety of faceted liposomes. Factors such as cooling rates and the careful choice of the liposome preparation method influence the formation of facets. Interdigitation was hypothesized as a main factor for the stabilization of facets and effectively monitored by small-angle X-ray scattering measurements.
| Fallah-Araghi, A., Meguellati, K., Baret, J. - C., El Harrak, A., Mangeat, T., Karplus, M., et al. (2014). Enhanced Chemical Synthesis at Soft Interfaces: A Universal Reaction-Adsorption Mechanism in Microcompartments. Physical Review Letters, 112(2).|
Abstract: A bimolecular synthetic reaction (imine synthesis) was performed compartmentalized in micrometer-diameter emulsion droplets. The apparent equilibrium constant (K-eq) and apparent forward rate constant (k(1)) were both inversely proportional to the droplet radius. The results are explained by a noncatalytic reaction-adsorption model in which reactants adsorb to the droplet interface with relatively low binding energies of a few k(B)T, react and diffuse back to the bulk. Reaction thermodynamics is therefore modified by compartmentalization at the mesoscale-without confinement on the molecular scale-leading to a universal mechanism for improving unfavorable reactions.
| Greenall, M. J., & Marques, C. M. (2014). Can adding oil control domain formation in binary amphiphile bilayers? Soft Matter, 10(40), 7925–7931.|
Abstract: Bilayers formed of two species of amphiphile of different chain lengths may segregate into thinner and thicker domains composed predominantly of the respective species. Using a coarse-grained mean-field model, we investigate how mixing oil with the amphiphiles affects the structure and thickness of the bilayer at and on either side of the boundary between two neighbouring domains. In particular, we find that oil molecules whose chain length is close to that of the shorter amphiphiles segregate to the thicker domain. This smooths the surface of the hydrophobic bilayer core on this side of the boundary, reducing its area and curvature and their associated free-energy penalties. The smoothing effect is weaker for oil molecules that are shorter or longer than this optimum value: short molecules spread evenly through the bilayer, while long molecules swell the thicker domain, increasing the surface area and curvature of the bilayer core in the interfacial region. Our results show that adding an appropriate oil could make the formation of domain boundaries more or less favourable, raising the possibility of controlling the domain size distribution.
| Marques, C., Weinberger, A., MacEwan, S., Schmatko, T., Schroder, A., & Chilkoti, A. (2014). Cargo Self-Assembly Controls Affinity Of Cell-Penetrating Peptides To Lipid Membranes. Journal Of Peptide Science, 20, S282.|
Keywords: Cell Penetrating Peptides; Elastin-like Polypetides; Giant Unilamellar Vesicles
| Mertins, O., Bacellar, I. O. L., Thalmann, F., Marques, C. M., Baptista, M. S., & Itri, R. (2014). Physical Damage on Giant Vesicles Membrane as a Result of Methylene Blue Photoirradiation. Biophysical Journal, 106(1), 162–171.|
Abstract: In this study we pursue a closer analysis of the photodamage promoted on giant unilamellar vesicles membranes made of dioleoyl-sn-glycero-3-phosphocholine (DOPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), by irradiating methylene blue present in the giant unilamellar vesicles solution. By means of optical microscopy and electro-deformation experiments, the physical damage on the vesicle membrane was followed and the phospholipids oxidation was evaluated in terms of changes in the membrane surface area and permeability. As expected, oxidation modifies structural characteristics of the phospholipids that lead to remarkable membrane alterations. By comparing DOPC- with POPC-made membranes, we observed that the rate of pore formation and vesicle degradation as a function of methylene blue concentration follows a diffusion law in the case of DOPC and a linear variation in the case of POPC. We attributed this scenario to the nucleation process of oxidized species following a diffusion-limited growth regime for DOPC and in the case of POPC a homogeneous nucleation process. On the basis of these premises, we constructed models based on reaction-diffusion equations that fit well with the experimental data. This information shows that the outcome of the photosensitization reactions is critically dependent on the type of lipid present in the membrane.
| Mukherji, D., Marques, C. M., & Kremer, K. (2014). Polymer collapse in miscible good solvents is a generic phenomenon driven by preferential adsorption. Nature Communications, 5.|
Abstract: Water and alcohol, such as methanol or ethanol, are miscible and, individually, good solvents for poly(N-isopropylacrylamide) (PNIPAm), but this polymer precipitates in water-alcohol mixtures. The intriguing behaviour of solvent mixtures that cannot dissolve a given polymer or a given protein, while the same macromolecule dissolves well in each of the cosolvents, is called cononsolvency. It is a widespread phenomenon, relevant for many formulation steps in the physicochemical and pharmaceutical industry, that is usually explained by invoking specific chemical details of the mixtures: as such, it has so far eluded any generic explanation. Here, by using a combination of simulations and theory, we present a simple and universal treatment that requires only the preferential interaction of one of the cosolvents with the polymer. The results show striking quantitative agreement with experiments and chemically specific simulations, opening a new perspective towards an operational understanding of macromolecular solubility.
| Sun, Y., Marques, C. M., & Schroder, A. P. (2014). Adhesion of giant unilamellar vesicles on double-end grafted DNA carpets. European Physical Journal-Special Topics, 223(9), 1755–1769.|
Abstract: We have recently shown that the bio-mimetic adhesion of Giant Unilamellar Vesicles on carpets of lambda-phage DNAs, grafted by one end to the substrate, leads to DNA scraping and stapling. As the lipid adhesion patch is built, outward forces stretch the DNA, while adhesion patch formation staples the chains into frozen conformations, trapped between the GUV membrane and the substrate. Analysis of the scraped and stapled DNA conformations provides a wealth of information about the membrane/polymer interactions at play during the formation of a bio-adhesive contact zone. In this paper we report new phenomena revealed by scraping and stapling phenomena associated with the bio-mimetic adhesion of Giant Unilamellar Vesicles on carpets of lambda-phage DNAs that were grafted to the substrate by both ends. In particular, the peculiar shapes of stapled DNA observed in this case, suggest that the membrane exerces not only outward radial forces during patch formation, but is is also able to confine the DNA molecules in the orthoradial direction.
| Weber, G., Charitat, T., Baptista, M. S., Uchoa, A. F., Pavani, C., Junqueira, H. C., et al. (2014). Lipid oxidation induces structural changes in biomimetic membranes. Soft Matter, 10(24), 4241–4247.|
Abstract: Oxidation can intimately influence and structurally compromise the levels of biological self-assembly embodied by intracellular and plasma membranes. Lipid peroxidation, a natural metabolic outcome of life with oxygen under light, is also a salient oxidation reaction in photomedicine treatments. However, the effect of peroxidation on the fate of lipid membranes remains elusive. Here we use a new photosensitizer that anchors and disperses in the membrane to achieve spatial control of the oxidizing species. We find, surprisingly, that the integrity of unsaturated unilamellar vesicles is preserved even for fully oxidized membranes. Membrane survival allows for the quantification of the transformations of the peroxidized bilayers, providing key physical and chemical information to understand the effect of lipid oxidation on protein insertion and on other mechanisms of cell function. We anticipate that spatially controlled oxidation will emerge as a new powerful strategy for tuning and evaluating lipid membranes in biomimetic media under oxidative stress.
| Balko, S. M., Kreer, T., Costanzo, P. J., Patten, T. E., Johner, A., Kuhl, T. L., et al. (2013). Polymer Brushes under High Load. Plos One, 8(3).|
Abstract: Polymer coatings are frequently used to provide repulsive forces between surfaces in solution. After 25 years of design and study, a quantitative model to explain and predict repulsion under strong compression is still lacking. Here, we combine experiments, simulations, and theory to study polymer coatings under high loads and demonstrate a validated model for the repulsive forces, proposing that this universal behavior can be predicted from the polymer solution properties.
| Bauer, M., Bernhardt, M., Charitat, T., Kekicheff, P., Fajolles, C., Fragneto, G., et al. (2013). Membrane insertion of sliding anchored polymers. Soft Matter, 9(5), 1700–1710.|
Abstract: We have studied the insertion into lipid bilayers of Sliding Anchored Polymers (SAPs), a new class of macromolecules based on topological complexes between end-capped polyethylene glycol (PEG) polymers and mono-cholesteryl cyclodextrins (CD). By using Infra Red Reflection Absorption Spectroscopy (IRRAS) we demonstrate that these new sliding polymer complexes anchor well in phospholipid model membranes self-assembled from DPPC. The in-plane organization is characterized by Brewster Angle Microscopy (BAM) at the air-water interface and by Atomic Force Microscopy (AFM) for lipid monolayers and for lipid bilayers deposited on mica. Demixing between SAPs and the phospholipids is observed even at low surface pressures. Using neutron reflectivity, we show that for sufficiently high polymer densities the SAPs inserted into lipid monolayers and lipid bilayers form polymer brushes, consistent with theoretical predictions for polymers with a sliding anchor.
| Greenall, M. J., & Marques, C. M. (2013). Can Amphiphile Architecture Directly Control Vesicle Size? Physical Review Letters, 110(8).|
Abstract: Bilayer membranes self-assembled from simple amphiphiles in solution always have a planar ground-state shape. This is a consequence of several internal relaxation mechanisms of the membrane and prevents the straightforward control of vesicle size. Here, we show that this principle can be circumvented and that direct size control by molecular design is a realistic possibility. Using coarse-grained calculations, we design tetrablock copolymers that form membranes with a preferred curvature and demonstrate how to form low-polydispersity vesicles while suppressing micellization. DOI: 10.1103/PhysRevLett.110.088301
| Jensen, I., Dantas, W. G., Marques, C. M., & Stilck, J. F. (2013). Pressure exerted by a grafted polymer on the limiting line of a semi-infinite square lattice. Journal of Physics a-Mathematical and Theoretical, 46(11).|
Abstract: Using exact enumerations of self-avoiding walks (SAWs) we compute the inhomogeneous pressure exerted by a two-dimensional end-grafted polymer on the grafting line which limits a semi-infinite square lattice. The results for SAWs show that the asymptotic decay of the pressure as a function of the distance to the grafting point follows a power law with an exponent similar to that of Gaussian chains and is, in this sense, independent of excluded volume effects.
| Meguellati, K., Fallah-Araghi, A., Baret, J. - C., El Harrak, A., Mangeat, T., Marques, C. M., et al. (2013). Enhanced imine synthesis in water: from surfactant-mediated catalysis to host-guest mechanisms. Chemical Communications, 49(96), 11332–11334.|
Abstract: An environment-responsive and fluorogenic reaction is reported and used as a model system to demonstrate experimentally three mechanisms of enhanced imine synthesis in water using either surfactants (below and above their CMC) or double-stranded DNA (acting as a reaction host).
| Weinberger, A., Tsai, F. - C., Koenderink, G. H., Schmidt, T. F., Itri, R., Meier, W., et al. (2013). Gel-Assisted Formation of Giant Unilamellar Vesicles. Biophysical Journal, 105(1), 154–164.|
Abstract: Giant unilamellar vesicles or GUVs are systems of choice as biomimetic models of cellular membranes. Although a variety of procedures exist for making single walled vesicles of tens of microns in size, the range of lipid compositions that can be used to grow GUVs by the conventional methods is quite limited, and many of the available methods involve energy input that can damage the lipids or other molecules present in the growing solution for embedment in the membrane or in the vesicle interior. Here, we show that a wide variety of lipids or lipid mixtures can grow into GUVs by swelling lipid precursor films on top of a dried polyvinyl alcohol gel surface in a swelling buffer that can contain diverse biorelevant molecules. Moreover, we show that the encapsulation potential of this method can be enhanced by combining polyvinyl alcohol-mediated growth with inverse-phase methods, which allow (bio)molecule complexation with the lipids.
| Greenall, M. J., & Marques, C. M. (2012). Hydrophobic droplets in amphiphilic bilayers: a coarse-grained mean-field theory study. Soft Matter, 8(12), 3308–3314.|
Abstract: Hydrophobic molecules such as oils and certain drugs can be encapsulated between the two leaflets of an amphiphilic bilayer in both lipid and polymer systems. We investigate the case where the hydrophobic molecules are incompatible with the amphiphile tails and so form droplets. Using a coarse-grained mean-field model (self-consistent field theory, or SCFT), we find that droplets of a wide range of sizes have the same characteristic lens shape, and explain this result in terms of simple capillarity arguments, consistent with the measured variations of surface concentrations of amphiphile in the bilayer and in the monolayers that cover the droplet. We study the effect of the strength chi(BO) of the repulsion between the hydrophobic liquid and the amphiphile tails on the droplet shape, and find a gradual flattening of the droplet as chi(BO) is reduced. The droplet remains at least metastable even at very low values of chi(BO). This is in contrast to the behavior as the length of the hydrophobic molecules is varied. Specifically, if these molecules are at least as long as the amphiphile tails, increasing their length further is found to have little effect on the droplet shape, while reducing their length below this value quickly causes the droplet to become unstable.
| Haluska, C. K., Baptista, M. S., Fernandes, A. U., Schroder, A. P., Marques, C. M., & Itri, R. (2012). Photo-activated phase separation in giant vesicles made from different lipid mixtures. Biochimica Et Biophysica Acta-Biomembranes, 1818(3), 666–672.|
Abstract: Using giant unilamellar vesicles (GUVs) made from POPC. DPPC, cholesterol and a small amount of a porphyrin-based photosensitizer that we name PE-porph, we investigated the response of the lipid bilayer under visible light, focusing in the formation of domains during the lipid oxidation induced by singlet oxygen. This reactive species is generated by light excitation of PE-porf in the vicinity of the membrane, and thus promotes formation of hydroperoxides when unsaturated lipids and cholesterol are present. Using optical microscopy we determined the lipid compositions under which GUVs initially in the homogeneous phase displayed Lo-Ld phase separation following irradiation. Such an effect is attributed to the in situ formation of both hydroperoxized POPC and cholesterol. The boundary line separating homogeneous Lo phase and phase coexistence regions in the phase diagram is displaced vertically towards the higher cholesterol content in respect to ternary diagram of POPC:DPPC:cholesterol mixtures in the absence of oxidized species. Phase separated domains emerge from sub-micrometer initial sizes to evolve over hours into large Lo-Ld domains completely separated in the lipid membrane. This study provides not only a new tool to explore the kinetics of domain formation in mixtures of lipid membranes, but may also have implications in biological signaling of redox misbalance. (C) 2011 Elsevier B.V. All rights reserved.
| Roth, A. E., Marques, C. M., & Durian, D. J. (2011). Abrasion of flat rotating shapes. Physical Review E, 83(3).|
Abstract: We report on the erosion of flat linoleum “pebbles” under steady rotation in a slurry of abrasive grit. To quantify shape as a function of time, we develop a general method in which the pebble is photographed from multiple angles with respect to the grid of pixels with a digital camera. This reduces digitization noise and allows the local curvature of the contour to be computed with a controllable degree of uncertainty. Several shape descriptors are then employed to follow the evolution of different initial shapes toward a circle, where abrasion halts. The results are in good quantitative agreement with a simple model, where we propose that points along the contour move radially inward in proportion to the product of the radius and the derivative of radius with respect to angle.
| Sun, Y. L., Mani, N. K., Baigl, D., Gisler, T., Schroeder, A. P., & Marques, C. M. (2011). Photocontrol of end-grafted lambda-phage DNA. Soft Matter, 7(12), 5578–5584.|
Abstract: We study the response to light stimulation of end-grafted lambda-phage DNAs in a solution of AzoTAB, a photosensitive compacting agent for the DNA chains. The biotinylated double-stranded DNA molecules are end-attached to a streptavidinated substrate and incubated in a 120 mM tris-borate-EDTA buffer in the presence of the cationic surfactant AzoTAB. We find that the conformations and the dynamics of the tethered DNAs can be tuned by the AzoTAB concentration and strongly depend on illumination conditions. Under visible light or in the dark AzoTAB is in a trans configuration and it induces DNA adsorption onto the substrate for [AzoTAB] >= 0.3 mM. In contrast, under UV illumination, AzoTAB is in a cis configuration and it induces DNA adsorption for [AzoTAB] >= 0.4 mM. In the AzoTAB concentration range 0.3-0.4 mM, one can thus reversibly switch between the adsorbed and the non-adsorbed states of the end-grafted chains by exposing the sample respectively to visible light (> 400 nm) and to UV illumination (365 nm). These light-induced adsorption transitions occur for AzoTAB concentrations approximately half of those required to control the DNA conformation in bulk solution, which highlights the predominance of chain-surface interactions over monomer-monomer intra-chain interactions for DNA molecules in the close vicinity of a solid substrate.
| Thalmann, F., Billot, V., & Marques, C. M. (2011). Lipid bilayer adhesion on sparse DNA carpets: Theoretical analysis of membrane deformations induced by single-end-grafted polymers. Physical Review E, 83(6).|
Abstract: We consider a single-end-grafted polymer chain covered by a membrane in contact with a flat and rigid surface in the context of supported membrane adhesion on surfaces carrying dilute polymer brushes. The fluid membrane adheres to the surface due to attractive interactions; the presence of a macromolecule locally hinders the membrane-surface contact and creates a protuberant membrane bulge. We study both the size and elevation of such membrane deformations as a function of curvature modulus, surface tension, adhesion energy, and chain size. Scaling results are derived, valid for both ideal and nonideal chain statistics, leading to complex diagrams of states depending on curvature modulus, tension, and adhesion values. We also compute quantitatively the membrane deformation profile for shallow bulges and make predictions for realistic systems involving DNA grafted chains covered by lipid membranes.
| Watkins, E. B., El-khouri, R. J., Miller, C. E., Seaby, B. G., Majewski, J., Marques, C. M., et al. (2011). Structure and Thermodynamics of Lipid Bilayers on Polyethylene Glycol Cushions: Fact and Fiction of PEG Cushioned Membranes. Langmuir, 27(22), 13618–13628.|
Abstract: In developing well hydrated polymer cushioned membranes, structural studies are often neglected. In this work, neutron and X-ray reflectivity studies reveal that hybrid bilayer/polyethylene glycol (PEG) systems created from mixtures of phospholipids and PEG conjugated lipopolymers do not yield a hydrated cushion beneath the bilayer unless the terminal ends of the lipopolymers are functionalized with reactive end groups and can covalently bind (tether) to the underlying support surface. While reactive PEG tethered systems yielded bilayers with near complete surface coverage, a bimodal distribution of heights with sub-micrometer lateral dimensions was observed consisting of cushioned membrane domains and uncushioned regions in close proximity to the support. The membrane fraction cushioned by the hydrated polymer could be controlled by adjusting the molar ratio of lipopolymer in the bilayer. A general phase diagram based on the free energy of the various configurations is derived that qualitatively predicts the observed behavior and the resulting structure of such systems a priori. As further evidenced by ellipsometry, atomic force and fluorescence microscopy, the tethered system provides a simple means for fabricating small cushioned domains within a membrane.
| Wolff, J., Marques, C. M., & Thalmann, F. (2011). Thermodynamic Approach to Phase Coexistence in Ternary Phospholipid-Cholesterol Mixtures. Physical Review Letters, 106(12).|
Abstract: We introduce a simple and predictive model for determining the phase stability of ternary phospholipid-cholesterol mixtures. Assuming that competition between the liquid and gel order of the phospholipids is the main driving force behind lipid segregation, we derive a Gibbs free energy of mixing, based on the thermodynamic properties of the lipids main transition. A numerical approach was devised that enables the fast and efficient determination of the ternary diagrams associated with our Gibbs free energy. The computed phase coexistence diagram of DOPC/DPPC/cholesterol reproduces well-known features for this system at 10 degrees C, as well as its evolution with temperature.
| Arnold, C., Thalmann, F., Marques, C., Marie, P., & Holl, Y. (2010). Surfactant Distribution in Waterborne Acrylic Films. 1. Bulk Investigation. J. Phys. Chem. B, 114(28), 9135–9147.|
Abstract: The distribution of an anionic surfactant, sodium dodecyl sulfate (SDS), in waterborne acrylic films was investigated, focusing on the effects of particle composition and size, and pH of the latex. The observed surfactant distributions could be classified in two categories: homogeneous and heterogeneous, the latter showing SDS aggregates. The shape of the profiles was related to the stability of the latex during drying, at short interparticular distances. The stability of the latex was determined by the presence or not of fixed charges at the surface of the particles. The latices with particles carrying neutralized acrylic acid at high pH (COO-) led to homogeneous distributions, whereas the latices with acrylic acid at low pH (COOH) or without acrylic acid led to heterogeneous distributions. Our interpretation is that the stable latices present a narrow network of paths between particles at high polymer volume fraction, limiting the mobility of the surfactant, whereas in the less stable latices wider routes between flocs allow enough mobility for large aggregate formation. Thermal treatments of the dry films confirmed the strong confinement of the surfactant in the dense film structure obtained at high pH and the more open structure, allowing easier surfactant transport and oxygen penetration, observed at low pH. In order to account for the shapes of the profiles more quantitatively, a model was developed based on the diffusion of the surfactant and its transport by the drying front. It was found that the apparent diffusion coefficient of SDS micelles had to be lowered to a great extent (D = 10(-13)-10(-14) m(2)/s) during drying in order to explain aggregate formation. It should be even lower (D = 10(-15) m(2)/s) to interpret homogeneous surfactant profiles. These results are consistent with our hypothesis of the key importance of the surfactant mobility during drying.
| Mendoza, C. I., Marques, C. M., & Thalmann, F. (2010). Enhanced shear separation for chiral magnetic colloidal aggregates. Phys. Rev. E, 82(6), 4 pp.|
Abstract: We study the designing principles of the simplest colloidal propeller, an architecture built from four identical spheres that can couple translation with rotation to produce controlled drift motion. By considering superparamagnetic beads, we show that the simultaneous action of a magnetic field and a shear flow leads to the migration of the cluster in the vorticity direction. We investigate the dependence of the migration velocity on the geometrical parameters of the cluster and find that significant cluster separation can be achieved under the typical operation conditions of microfluidic devices.
| Nam, G., Hisette, M. L., Sun, Y. L., Gisler, T., Johner, A., Thalmann, F., et al. (2010). Scraping and Stapling of End-Grafted DNA Chains by a Bioadhesive Spreading Vesicle to Reveal Chain Internal Friction and Topological Complexity. Prl, 105(8), 088101.|
Abstract: Stained end-grafted DNA molecules about 20  μm long are scraped away and stretched out by the spreading front of a bioadhesive vesicle. Tethered biotin ligands bind the vesicle bilayer to a streptavidin substrate, stapling the DNAs into frozen confinement paths. Image analysis of the stapled DNA gives access, within optical resolution, to the local stretching values of individual DNA molecules swept by the spreading front, and provides evidence of self-entanglements.
| Campillo, C. C., Schroder, A. P., Marques, C. M., & Pepin-Donat, B. (2009). Composite gel-filled giant vesicles: Membrane homogeneity and mechanical properties. Materials Science & Engineering C-Biomimetic And Supramolecular Systems, 29(2), 393–397.|
Abstract: We further investigate the properties of composite Poly(NIPAM) poly(N-isopropylacrylamide)) gel-filled giant vesicles, focusing here on i) the homogeneity of the membrane, ii) its coupling to the inner gel under strong suction pressures, and iii) the relation between the final elastic modulus of the vesicles and the amount of crosslinker in the pre-gel medium. We show that whereas the photo-polymerization process induces a decrease of the membrane homogeneity at the micrometer size range. the membrane still remains strongly coupled to the internal gel network. The vesicles studied here display average moduli in the range [0.5-25] kPa. confirming their potential as biomimetic mechanical systems. (C) 2008 Elsevier B.V. All rights reserved.
| Mertins, O., da Silveira, N. P., Pohlmann, A. R., Schroder, A. P., & Marques, C. M. (2009). Electroformation of Giant Vesicles from an Inverse Phase Precursor. Biophysical Journal, 96(7), 2719–2726.|
Abstract: We discuss a simple modification of the well-known method of giant vesicle electroformation that allows for a direct addition of water-soluble species to the phospholipid bilayers. Using this modified method, we prepare phospholipid vesicles decorated with chitosan, a water-soluble polysaccharide currently investigated for potential pharmacological applications. We find that the method allows this polysaccharide with primary amino groups on every glucose subunit to be tightly bound to the membrane, rather than simply being encapsulated.
| Riske, K. A., Sudbrack, T. P., Archilha, N. L., Uchoa, A. F., Schroder, A. P., Marques, C. M., et al. (2009). Giant Vesicles under Oxidative Stress Induced by a Membrane-Anchored Photosensitizer. Biophysical Journal, 97(5), 1362–1370.|
Abstract: We have synthesized the amphiphile photosensitizer PE-porph consisting of a porphyrin bound to a lipid head-group. We studied by optical microscopy the response to light irradiation of giant unilamellar vesicles of mixtures of unsaturated phosphatidylcholine lipids and PE-porph. In this configuration, singlet oxygen is produced at the bilayer surface by the anchored porphyrin. Under irradiation, the PE-porph decorated giant unilamellar vesicles exhibit a rapid increase in surface area with concomitant morphological changes. We quantify the surface area increase of the bilayers as a function of time and photosensitizer molar fraction. We attribute this expansion to hydroperoxide formation by the reaction of the singlet oxygen with the unsaturated bonds. Considering data from numeric simulations of relative area increase per phospholipid oxidized (15%), we measure the efficiency of the oxidative reactions. We conclude that for every 270 singlet oxygen molecules produced by the layer of anchored porphyrins, one eventually reacts to generate a hydroperoxide species. Remarkably, the integrity of the membrane is preserved in the full experimental range explored here, up to a hydroperoxide content of 60%, inducing an 8% relative area expansion.
| Campillo, C. C., Schroder, A. P., Marques, C. M., & Pepin-Donat, B. (2008). Volume transition in composite poly(NIPAM)-giant unilamellar vesicles. Soft Matter, 4(12), 2486–2491.|
Abstract: We have recently reported on the formation of composite gel vesicles prepared by the photopolymerization and crosslinking of poly(N-isopropyl-acrylamide) [poly(NIPAM)] inside phospholipid giant unilamellar vesicles (GUVs). Here we present a detailed study of the thermo-responsive behaviour of such composite vesicles. Giant vesicles filled with a poly(NIPAM) gel (gel-GUVs) exhibit a global volume phase transition, revealing a strong interaction between the gel and the phospholipid bilayer. Fluorescence studies show that the lipid membrane is not destroyed during the volume transition. The behaviour of giant vesicles filled with a poly(NIPAM) solution (sol-GUVs) depends on the volume fraction phi(NIPAM) of encapsulated NIPAM, the precursor monomer for poly(NIPAM). For phi(NIPAM) <= 0.06, we observe a frustrated demixing of the poly(NIPAM) chains in the internal medium; for phi(NIPAM) >= 0.07, sol-GUVs behave like homogeneous spheres and undergo a global volume phase transition similar to the one observed in gel-GUVs. For high volume fractions (phi(NIPAM) = 0.09) achieved by osmotic deflation of low volume fraction (phi(NIPAM) = 0.03) sol-GUVs, we observe a full demixing of the internal medium into two well-separated phases.
| Cohen-Tannoudji, L., Bertrand, E., Baudry, J., Robic, C., Goubault, C., Pellissier, M., et al. (2008). Measuring the kinetics of biomolecular recognition with magnetic colloids. Physical Review Letters, 100(10), 108301.|
Abstract: We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.
| Haluska, C. K., Schroder, A. P., Didier, P., Heissler, D., Duportail, G., Mely, Y., et al. (2008). Combining Fluorescence Lifetime and Polarization Microscopy to Discriminate Phase Separated Domains in Giant Unilamellar Vesicles. Biophysical Journal, 95(12), 5737–5747.|
Abstract: Using fluorescence lifetime microscopy we study the structure of lipid domains in giant unilamellar vesicles made from sphingomyelin, 1,2-dioleoyl-sn-glycero-3-phosphocholine, and cholesterol. Lifetimes and orientation of a derivative of the fluorescent probe DPH embedded in the membrane were measured for binary and ternary lipid mixtures incorporating up to 42 mol % of cholesterol. The results show that adding cholesterol always increases the lifetime of the probe studied. In addition, the analysis of the probe orientation indicates that cholesterol has little influence on the ordering of the sphingomyelin alkyl chains whereas it has a noticeable effect on the structure of the 1,2-dioleoyl-sn-glycero-3-phosphocholine chains. The measurements made on the orientation and lifetime of the probe show the structure of the membrane in its liquid ordered and liquid disordered domains.
| Hisette, M. L., Haddad, P., Gisler, T., Marques, C. M., & Schroder, A. P. (2008). Spreading of bio-adhesive vesicles on DNA carpets. Soft Matter, 4(4), 828–832.|
Abstract: Cell-adhesion events involve often the formation of a contact region between phospholipid membranes decorated with a variety of bio-macromolecular species. We mimic here such hairy bio-adhesive contact zones by spreading phospholipid vesicles onto surfaces carpeted with end-grafted lambda-phage DNA. Our study reveals that the spreading front acts as a scraper that strongly stretches the DNA molecules, and that the multiple bonds created during vesicle spreading effectively staple the stretched chains in the gap between the membrane and the substrate. The scraping and stapling mechanisms revealed here for the long DNA molecules are expected to also play a role in actual bio-adhesion events of cell walls and tissues.
| Lee, N. K., Johner, A., Thalmann, F., Cohen-Tannoudji, L., Bertrand, E., Baudry, J., et al. (2008). Ligand-receptor interactions in chains of colloids: When reactions are limited by rotational diffusion. Langmuir, 24(4), 1296–1307.|
Abstract: We discuss the theory of ligand receptor reactions between two freely rotating colloids in close proximity to one other. Such reactions, limited by rotational diffusion, arise in magnetic bead suspensions where the beads are driven into close contact by an applied magnetic field as they align in chainlike structures. By a combination of reaction-diffusion theory, numerical simulations, and heuristic arguments, we compute the time required for a reaction to occur in a number of experimentally relevant situations. We find in all cases that the time required for a reaction to occur is larger than the characteristic rotation time of the diffusion motion tau(rot). When the colloids carry one ligand only and a number n of receptors, we find that the reaction time is, in units of tau(rot), a function simply of n and of the relative surface alpha occupied by one reaction patch alpha = pi rc(2)/(4 pi r(2)), where r(c) is the ligand receptor capture radius and r is the radius of the colloid.
| Baulin, V. A., Marques, C. M., & Thalmann, F. (2007). Collision induced spatial organization of microtubules. Biophysical Chemistry, 128(2-3), 231–244.|
Abstract: The dynamic behavior of microtubules in solution can be strongly modified by interactions with walls or other structures. We examine here a microtubule growth mode I where the increase in size of the plus-end is perturbed by collisions with other microtubules. We show that such a simple mechanism of constrained growth can induce ordered structures and patterns from an initially isotropic and homogeneous suspension. We find that microtubules self-organize locally in randomly oriented domains that grow and compete with each other. A weak orientation bias, similar to the one induced by gravity or cellular boundaries is enough to influence the domain growth direction, eventually leading to a macroscopic sample orientation. (c) 2007 Elsevier B.V. All rights reserved.
| Caetano, W., Haddad, P. S., Itri, R., Severino, D., Vieira, V. C., Baptista, M. S., et al. (2007). Photo-induced destruction of giant vesicles in methylene blue solutions. Langmuir, 23(3), 1307–1314.|
Abstract: We study the photodecomposition of phospholipid bilayers in aqueous solutions of methylene blue. Observation of giant unilamellar vesicles under an optical microscope reveals a consistent pattern of membrane disruption as a function of methylene blue concentration and photon density for different substrates supporting the vesicles.
| Durian, D. J., Bideaud, H., Duringer, P., Schroder, A. P., & Marques, C. M. (2007). Shape and erosion of pebbles. Physical Review E, 75(2), 021301.|
Abstract: The shapes of flat pebbles may be characterized in terms of the statistical distribution of curvatures measured along their contours. We illustrate this method for clay pebbles eroded in a controlled laboratory apparatus, and also for naturally occurring rip-up clasts formed and eroded in the Mont St.-Michel bay. We find that the curvature distribution allows finer discrimination than traditional measures of aspect ratios. Furthermore, it connects to the microscopic action of erosion processes that are typically faster at protruding regions of high curvature. We discuss in detail how the curvature may be reliably deduced from digital photographs.
| Baulin, V. A., Lee, N. K., Johner, A., & Marques, C. M. (2006). Micellization of sliding polymer surfactants. Macromolecules, 39(2), 871–876.|
Abstract: Following up a recent paper oil grafted sliding polymer layers [Macromolecules 2005, 38, 1434-1441], we investigated the influence of the sliding degree of freedom oil the self-assembly of sliding polymeric surfactants that can be obtained by complexation of polymers with cyclodextrins. In contrast to the micelles of quenched block copolymer surfactants, the free energy of micelles of sliding surfactants can exhibit two minima: the first corresponding to small micelles with symmetric arm lengths and the second corresponding to large micelles with asymmetric arm lengths. The relative sizes and concentrations of small and large micelles in the solution depend on the molecular parameters of the system. The appearance of small micelles drastically reduces the kinetic barrier, allowing for the fast formation of equilibrium micelles.
| Bickel, T., & Marques, C. M. (2006). Entropic interactions in soft nanomaterials. Journal Of Nanoscience And Nanotechnology, 6(8), 2386–2395.|
Abstract: We review the forces that rule interactions between phospholipid membranes and other soft nanomaterials such as polymers and colloids. Contrary to traditional nanostructures, soft materials display a high susceptibility to the fluctuations of the thermal environment, leading to new forces of an essentially entropic nature.
| Durian, D. J., Bideaud, H., Duringer, P., Schroder, A., Thalmann, F., & Marques, C. M. (2006). What is in a pebble shape? Phys. Rev. Lett., 97(2), 4 pp.|
Abstract: We propose to characterize the shapes of flat pebbles in terms of the statistical distribution of curvatures measured along the pebble contour. This is demonstrated for the erosion of clay pebbles in a controlled laboratory apparatus. Photographs at various stages of erosion are analyzed, and compared with two models. We find that the curvature distribution complements the usual measurement of aspect ratio, and connects naturally to erosion processes that are typically faster at protruding regions of high curvature.
| Likthman, A. E., & Marques, C. M. (2006). First-passage problem for the Rouse polymer chain: An exact solution. Europhysics Lett., 75(6), 971–977.|
Abstract: We solve the first-passage problem of a non-Markovian process arising in the reaction diffusion theory of polymer chains. By considering the Rouse chain, a free-draining dynamic model of a polymer where the chain monomers are represented by beads and the chain connectivity by harmonic springs, we develop an exact analytical method for describing the kinetics of end-chain reactions. Our analytical results illuminate the approximations used previously and are in perfect agreement with numerical stochastic simulations.
| Zana, R., Marques, C., & Johner, A. (2006). Dynamics of micelles of the triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in aqueous solution. Advances In Colloid And Interface Science, 123, 345–351.|
Abstract: A number of results reported on the kinetics of exchange of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, between micelles and the intermicellar aqueous solution are reviewed and analyzed to extract the rate constants k(+) for the entry of a copolymer into a micelle and k(-) for the exit of a copolymer from a micelle. Contrary to what is generally observed for conventional surfactants, the rate constant for the entry of a copolymer into a micelle is slower to much slower than for a diffusion-controlled process and decreases as the degree of polymerization of the PO block, n(PO), increases. The effect of the degree of polymerization of the EO block, n(EO), on the two rate constants is significant only for low values of n(EO). The variation of k(-) with n(PO) strongly suggests that the free copolymer molecule adopts a conformation where the PO block is tightly coiled with little contact with water and not a fully extended and hydrated conformation, in contrast to what is commonly assumed when analyzing the dependence of the cmc on the polymerization degree of the hydrophobic block. (c) 2006 Elsevier B.V. All rights reserved.
| Baulin, V. A., Johner, A., & Marques, C. M. (2005). Sliding grafted polymer layers. Macromolecules, 38(4), 1434–1441.|
Abstract: We study theoretically the structure of sliding grafted polymer layers, or SGP layers. These interfacial structures are built by attaching each polymer to the substrate with a ringlike molecule such as cyclodextrins. Such a topological grafting mode allows the chains to freely slide along the attachment point. Escape from the sliding link is prevented by bulky capping groups. We show that grafts in the mushroom regime adopt mainly symmetric configurations (with comparable branch sizes), while grafts in dense layers are highly dissymmetric so that only one branch per graft participates in the layer. Sliding layers on small colloids or starlike sliding micelles exhibit an intermediate behavior, where the number of longer branches participating in the corona is independent of the total number of branches. This regime also exists for sliding surface micelles comprising less chains, but it is narrower.
| Gomez, E. D., Rappl, T. J., Agarwal, V., Bose, A., Schmutz, M., Marques, C. M., et al. (2005). Platelet self-assembly of an amphiphilic A-B-C-A tetrablock copolymer in pure water. Macromolecules, 38(9), 3567–3570.|
| Izzo, D., & Marques, C. M. (2005). Solubilization of homopolymers in a solution of diblock copolymers. J. Phys. Chem. B, 109(13), 6140–6145.|
Abstract: We study theoretically mixed solutions of homopolymer and diblock copolymer chains. The solvent is a poor solvent for the homopolymers and a selective solvent for the copolymers. We find that the formation of copolymer micelles containing also the insoluble chains allows for an increased solubility of the homopolymers in the solution. In agreement with experiments, we find also that the solubilization power of the micelles, that is, the maximum amount of total homopolymer weight solubilized per unit weight of copolymers in solution, decreases strongly with the homopolymer index of polymerization.
| Fa, N., Marques, C. M., Mendes, E., & Schroder, A. P. (2004). Rheology of giant vesicles: A micropipette study. Phys. Rev. Lett., 92(10), 4 pp.|
Abstract: We develop a micropipette rheometer to study the effect of oscillatory shear flow on the spontaneous fluctuations of phospholipid bilayers. Our results on giant vesicles show that oscillatory shear flow leads to a suppression of membrane fluctuations. They also imply that the Helfrich equation is modified in the presence of the flow. This equation, a fundamental constitutive relation between the amount of area stored in the fluctuations and the membrane tension, must be supplemented under oscillatory shear by a flow excess function that we determine.
| Mendoza, C. I., & Marques, C. M. (2004). Fluctuating diffusion-limited aggregates. Physica A, 335(3-4), 305–313.|
Abstract: We study the structure and growth of a diffusion-limited aggregate (DLA) for which the constitutive units remain mobile during the aggregation process. Contrary to DLA where far from equilibrium conditions are the prevalent factor for growth, the structure of the aggregate is here determined by a combination of annealed and quenched processes. The internal flexibility allows the aggregate to span the equilibrium configurational space, and such thermally driven motion further modifies the connectivity statistics of the growing branched structure. (C) 2003 Elsevier B.V. All rights reserved.
Keywords: diffusion-limited aggregates; fluctuation phenomena; colloids
| Moreira, A. G., & Marques, C. M. (2004). The role of polymer spacers in specific adhesion. J. Chem. Phys., 120(13), 6229–6237.|
Abstract: We study the role of flexible spacers in specific adhesion from the point of view of polymer reaction-diffusion theory. By assuming that the interactions between complementary adhesion moieties occur on a length scale much smaller than the size of the polymer spacer, we describe in detail binding and rupture between two opposing surfaces. Predictions are given for the physical properties of interest such as the time evolution of bond density and the ranges of attraction and unbinding. We also discuss the dynamic crossover between reversible and irreversible bridging. (C) 2004 American Institute of Physics.
| Beckrich, P., Weick, G., Marques, C. M., & Charitat, T. (2003). Compression modulus of macroscopic fiber bundles. Europhysics Lett., 64(5), 647–653.|
Abstract: We study dense, disordered stacks of elastic macroscopic fibers. These stacks often exhibit non-linear elasticity, due to the coupling between the applied stress and the internal distribution of fiber contacts. We propose a theoretical model for the compression modulus of such systems, and illustrate our method by studying the conical shapes frequently observed at the extremities of ropes and other fiber structures.
| Moreira, A. G., Jeppesen, C., Tanaka, F., & Marques, C. M. (2003). Irreversible vs. reversible bridging: When is kinetics relevant for adhesion? Europhysics Lett., 62(6), 876–882.|
Abstract: We study theoretically the adhesion between two approaching surfaces, one containing tethered ligands and the other receptors. Using the reaction-diffusion formalism, we show that the range of adhesion l(r) is generally determined by a combination of tether dynamics, ligand-receptor affinity and experimental speed of approach v. Contrary to previous studies, we fully account for back reactions and are thus able to describe the crossover between irreversible adhesion at large affinities or high speed v and reversible adhesion at small affinities or low speed. We also briefly discuss the case of rupture and show that in the limit of irreversible adhesion the rupture occurs always at a larger distance than l(r) determined for approaching surfaces.
| Balsara, N. P., Marques, C. M., Garetz, B. A., Newstein, M. C., & Gido, S. P. (2002). Anisotropy of lamellar block copolymer grains. Phys. Rev. E, 66(5), 4 pp.|
Abstract: The Wulff construction and the theory of Milner and Morse [Phys. Rev. E 54, 3793 (1996)] were used to calculate the shape of grains formed when a lamellar block copolymer phase is formed by a shallow quench into the ordered state. The calculations show that the grains are ellipsoids of revolution, with an aspect ratio rho=2.37. This value is in reasonable agreement with results of transmission electron microscopy and depolarized light scattering experiments, which indicate that the average value of rho of grains formed during the early stages of the disorder-to-order transition is about 2.0.
| Bickel, T., & Marques, C. M. (2002). Scale-dependent rigidity of polymer-ornamented membranes. Eur. Phys. J. E, 9(4), 349–352.|
Abstract: We study the fluctuation spectrum of fluid membranes carrying grafted polymers. Contrary to usual descriptions, we find that the modifications induced by the polymers cannot be reduced to the renormalization of the membrane bending rigidity. Instead we show that the ornamented membrane exhibits a scale-dependent elastic modulus that we evaluate. In ornamented lamellar stacks, we further compute the polymer contribution to the Caille parameter characterizing the power law singularities of the Bragg peaks.
| Israelachvili, J. N., Jeppesen, C., Wong, J. Y., Kuhl, T., Mullah, N., Zalipsky, S., et al. (2002). Dynamics of tethered ligand-receptor bond formation. Biophys. J., 82(1), 40.|
| Mendoza, C. I., & Marques, C. M. (2002). Scattering from supramacromolecular structures. Phys. Rev. E, 66(5), 8 pp.|
Abstract: We study theoretically the scattering imprint of a number of branched supramacromolecular architectures, namely, polydisperse stars and dendrimeric, hyperbranched structures. We show that polydispersity and nature of branching highly influence the intermediate wave vector region of the scattering structure factor, thus providing insight into the morphology of different aggregates formed in polymer solutions.
| Bickel, T., Jeppesen, C., & Marques, C. M. (2001). Local entropic effects of polymers grafted to soft interfaces. Eur. Phys. J. E, 4(1), 33–43.|
Abstract: In this paper, we study the equilibrium properties of polymer chains end-tethered to a fluid membrane. The loss of conformational entropy of the polymer results in an inhomogeneous pressure field that we calculate for Gaussian chains. We estimate the effects of excluded volume through a relation between pressure and concentration. Under the polymer pressure, a soft surface will deform. We calculate the deformation profile for a fluid membrane and show that close to the grafting point, this profile assumes a cone-like shape, independently of the boundary conditions. Interactions between different polymers are also mediated by the membrane deformation. This pair-additive potential is attractive for chains grafted on the same side of the membrane and repulsive otherwise.
| Jeppesen, C., Wong, J. Y., Kuhl, T. L., Israelachvili, J. N., Mullah, N., Zalipsky, S., et al. (2001). Impact of polymer tether length on multiple ligand-receptor bond formation. Science, 293(5529), 465–468.|
Abstract: The promoters of cell adhesion are ligands, which are often attached to flexible tethers that bind to surface receptors on adjacent cells. Using a combination of Monte Carte simulations, diffusion reaction theory, and direct experiments (surface force measurements) of the biotin-streptavidin system, we have quantified polymer chain dynamics and the kinetics and spatial range of tethered ligand-receptor binding. The results show that the efficiency of strong binding does not depend solely on the molecular architecture or binding energy of the receptor-ligand pair, nor on the equilibrium configuration of the polymer tether, but rather on its “rare” extended conformations.
| Marques, C. M., Wong, J. Y., Kuhl, T. L., Jeppesen, C., Israelachvili, J. N., Mullah, N., et al. (2001). Dynamics of tethered ligand-receptor interactions. In Abstracts Of Papers Of The American Chemical Society (Vol. 221, 324-COLL). Amer Chemical Soc.|
| Yang, B. S., Lal, J., Richetti, P., Marques, C. M., Russel, W. B., & Prud'homme, R. K. (2001). Interaction of hydrophobically modified polymers and surfactant lamellar phase. Langmuir, 17(19), 5834–5841.|
Abstract: We investigate the effect of polysoaps on the phase behavior and membrane elastic properties of the lyotropic lamellar (L-alpha) phase of the nonionic surfactant penta(ethylene glycol) dodecyl ether (C12E5). The polysoap is a hydrophobically modified polymer (hm-polymer) with n-alkyl side groups randomly grafted to a polyacrylate (PAA) backbone. The membrane properties are extracted from small-angle neutron scattering data based on a model developed by Nallet et al. and the excess area method developed by Roux et al. The phase behavior, membrane rigidity, compression modulus, and bilayer mean bending modulus are found to be independent of molecular weight, polydispersity, and hydrophobe length of hm-polymers. The rigidity and compression moduli of membranes increase with increasing polymer concentration and hydrophobe substitution level. A minimum hydrophobic interaction strength (combination of hydrophobe length and hydrophobe substitution level) is required to produce single phase polysoap/lamellar surfactant systems. A scaling model is proposed that defines the boundaries between homogeneous and biphasic solutions based on two criteria: (1) the surface coverage of chain segments between hydrophobus (i.e. blobs) must be less than the available membrane area and (2) the interlamellar spacing must be larger than the blob size. This simple model captures the essential features of the phase diagrams.
| Bickel, T., Marques, C., & Jeppesen, C. (2000). Grafted polymers are miniaturized pressure tools. C. R. Acad. Sci. Ser. IV-Phys. Astrophys., 1(5), 661–664.|
Abstract: Development of techniques to characterize and manipulate matter at the mesoscopic level (1-10(3) nm) has been the cornerstone of recent technological and scientific progress in biology, physics and chemistry. Many of the techniques rely on the possibility of applying well defined forces at the relevant lengths scales: revealing the structure of colloidal interactions with a surface force apparatus (SFA) (Israelachvili J., Intermolecular and Surface Forces, Academic Press, London, 1992); imaging biologic and other soft materials with an atomic force microscope (AFM) (Binnig G., Quate C.F, Gerber C., Phys. Rev. Lett. 56 (1986) 930); manipulating DNA, vesicles or emulsions with optical tweezers (Ashkin A., Dziedzic J., Bjorkholm J.M., Chu S., Opt. Lett. 11 (1986) 288)... We argue hen that grafted polymers rightfully belong to the family of mesoscopic force tools, and predict the forces that these tools are expected to exert in a number of experimental situations. (C) 2000 Academie dcs scicnces/Editions scientifiques et medicales Elsevier SAS.
Keywords: grafted polymers; pressure tools; surfaces; membranes
| Bickel, T., Marques, C., & Jeppesen, C. (2000). Pressure patches for membranes: The induced pinch of a grafted polymer. Phys. Rev. E, 62(1), 1124–1127.|
Abstract: Achieving control of membrane shape and topology is of crucial importance to regulate function and performance of many systems in the realms of biology, physics, and chemical sciences. The design of a kit of versatile microscopic tools for tuning the shapes of fluid membranes relies ultimately on the possibility of tailoring molecules for applying a given, well-chosen force, to the self-assembled interfaces. Here we discuss theoretically the ability of grafted polymers to perform as mesoscopic pressure patches. We compute the pressure that a grafted polymer applies to the supporting surface. We also show that this entropic pressure leads to a well-defined pinched form of the membranes. Moreover. new membrane-mediated forces result from the action of these pressure tools, enabling action upon their spatial distribution along the membrane surface.
| Gittings, M. R., Cipelletti, L., Trappe, V., Weitz, D. A., In, M., & Marques, C. (2000). Structure of guar in solutions of H2O and D2O: An ultra-small-angle light-scattering study. J. Phys. Chem. B, 104(18), 4381–4386.|
Abstract: We examine the structure of guar as a function of concentration in both H2O and D2O using several different scattering techniques. The range of scattering vectors spans 5 decades (143 cm(-1) < q < 10.3 x 10(6) cm(-1)), providing insight into the supramolecular and local, organization of the chains. This allows us to directly characterize the large-scale aggregate structure of the guar, which can be on the order of 100 μm. The aggregates are most likely loosely interconnected with single chains and other aggregates, and the structure and organization are critical in determining solution viscoelastic properties. The solubility is poorer in D2O, as evidenced by larger aggregates, higher scattering intensities, a slightly higher fractal dimension, and a sublinear concentration dependence of the intensity. Aggregates were found in dilute neutral guar solutions as well as in cationic guar solutions (in H2O), whether screened or unscreened. The presence of aggregates at all concentrations for neutral and charged guar indicates the difficulty in determining a molecular weight of the guar molecule.
| Robelin, C., Anthony, O., Marques, C., & Richetti, P. (1999). Bulk and surface behavior of polymer-surfactant solutions: Cationic guar and sodium dodecyl sulfate. In Abstracts Of Papers Of The American Chemical Society (Vol. 218, 114-COLL). Amer Chemical Soc.|
| Anthony, O., Marques, C. M., & Richetti, P. (1998). Bulk and surface behavior of cationic guars in solutions of oppositely charged surfactants. Langmuir, 14(21), 6086–6095.|
Abstract: We study the bulk and surface behavior of aqueous mixtures of cationic guars and anionic sulfate surfactants. The phase diagrams are determined and the phases characterized with a variety of techniques. When the surfactant is gradually added, the polyelectrolyte is physically modified by ionic binding of the surfactant or more likely surfactant aggregates to the polymer chains. This results in the increase of the solution viscosity and leads to phase separation between a polymer- and surfactant-rich phase and a dilute supernatant; Phase separation always occurs for surfactant concentrations below the critical micelle concentration (cmc). A second one-phase region is obtained for surfactant concentration as low as twice the cmc, independent of the polymer charge density or of the alkyl chain length of the sulfate surfactant. The surface behavior is investigated with a surface forces apparatus. The force profiles between two layers of cationic guar preadsorbed onto mica surfaces are measured in water and in surfactant solutions for concentrations covering the three regions of the bulk-phase diagram. We conclude that the structure of the adsorbed layers is clearly related to the structure of the corresponding polymer/surfactant mixtures.
| Gittings, M. R., Marques, C., & Derian, P. J. (1998). Characterization and solubility properties of guar. In Abstracts Of Papers Of The American Chemical Society (Vol. 216, 029-CELL). Amer Chemical Soc.|
| Marques, C. M., Izzo, D., Charitat, T., & Mendes, E. (1998). Scattering from solutions of star polymers. European Physical Journal B, 3(3), 353–358.|
Abstract: We study the scattering intensity of dilute and semi-dilute solutions of star polymers. The star conformation is described by a model introduced by Daoud and Cotton. In this model, a single star is regarded as a spherical region of a semi-dilute polymer solution with a local, position dependent screening length. For high enough concentrations, the outer sections of the arms overlap and build a semi-dilute solution (a sea of blobs) where the inner parts of the actual stars are embedded. The scattering function is evaluated following a method introduced by Auvray and de Gennes. In the dilute regime there are three regions in the scattering function: the Guinier region (low wave vectors, qR much less than 1) from where the radius of the star can be extracted, the intermediate region (1 much less than qR f(2/5)) that carries the signature of the form factor of a star with f arms: I(q) N similar to q(-10/3); and a high wavevector zone (qR much greater than f(2/5)) where the local swollen structure of the polymers gives rise to the usual q(-5/3) decay. In the semi-dilute regime the different stars interact strongly, and the scattered intensity acquires two new features: a liquid peak that develops at a reciprocal position corresponding to the star-star distances; and a new large wavevector contribution of the form q(-5/3) originating from the sea of blobs.
| Prud'homme, R., Marques, C. M., Richetti, P., & Yang, Y. (1998). Confinement of hydrophobically modified polyacrylates into nonionic surfactant lyostropic bilayers. In Abstracts Of Papers Of The American Chemical Society (Vol. 216, 028-COLL). Amer Chemical Soc.|
| Prud'homme, R., Yang, Y., Marques, C. M., & Richetti, P. (1998). Confinement of hydrophobically modified polyacrylates into nonionic surfactant lyostropic bilayers. In Abstracts Of Papers Of The American Chemical Society (Vol. 216, 199-PMSE). Amer Chemical Soc.|
| Yaman, K., Jeppesen, C., & Marques, C. M. (1998). Depletion forces between two spheres in a rod solution. Europhysics Lett., 42(2), 221–226.|
Abstract: We study the depletion interaction between spherical particles of radius R immersed in a dilute solution of rigid rods of length L. The computed interaction potential is, within numerical accuracy, exact for any value of L/R. In particular we find that for L similar to R, the depth of the depletion well is smaller than the prediction of the Derjaguin approximation. Our results bring new light into the discussion on the lack of phase separation in colloidal mixtures of spheres and rods.
| Yang, Y., Prud'homme, R. K., Marques, C. M., & Richetti, P. (1998). Confinement of polysoaps in nonionic surfactant bilayers. In Abstracts Of Papers Of The American Chemical Society (Vol. 215, 229-COLL). Amer Chemical Soc.|
| Yang, Y., Prudhomme, R., McGrath, K. M., Richetti, P., & Marques, C. M. (1998). Confinement of polysoaps in membrane lyotropic phases. Phys. Rev. Lett., 80(12), 2729–2732.|
Abstract: We study the confinement of polysoaps in lyotropic smectic (L-alpha) and sponge (L-3) solutions of the nonionic surfactant pentaethylene glycol dodecyl ether (C12EO5) The polysoap is a hydrophobically modified polymer with n-tetradecyl sidegroups randomly grafted to a polyacrylate backbone. Without the hydrophobic side chains the backbone polymer cannot be embedded into the intermembrane space, but confinement is achieved for a polysoap with as low as 1% of grafted groups. We measure by small angle x-ray and neutron scattering an increase of the bending rigidity of the lamellar membranes as a function of polysoap concentration.
| Anthony, O., Marques, C., & Richetti, P. (1997). Bulk and surface behavior of cationic guar and sodium dodecyl sulfate. In Abstracts Of Papers Of The American Chemical Society (Vol. 213, 224-COLL). Amer Chemical Soc.|
| Izzo, D., & Marques, C. M. (1997). Selectively swollen phases of diblock copolymers. Macromolecules, 30(21), 6544–6549.|
Abstract: We study the aggregation of diblock copolymers in a selective solvent as a function of the asymmetry of the copolymer chains. When the shorter block is in a poor solvent, our mean-field approach predicts copolymer micellization in spherical or cylindrical geometries. For large collapsed blocks a dense lamellar phase is formed in an excess of solvent. A further increase of the size of the molten blocks leads to the formation of reverse micellar structures, where small spherical swollen cores are surrounded by a majority matrix of molten chains.
| Mendes, E., Schadler, V., Marques, C. M., Lindner, P., & Wiesner, U. (1997). Electrostatics in the self-assembly of macromolecular surfactants. Europhysics Lett., 40(5), 521–526.|
Abstract: We report on a small-angle neutron scattering (SANS: study of dilute solutions of neutral and charged polystyrene-polyisoprene (PS-b-PI) diblock copolymers in dimethyl acetamide (DMAc), a polar selective solvent for PS. This is a model macromolecular surfactant system: the low glass temperature of the PI block ensures that thermodynamic equilibrium can be attained; the ionic character of the copolymers is provided by a single sulfonate group at the free chain end of the PI block. The crossover From ionic to non-ionic behaviour is investigated by addition of salt. The results are compared to theoretical predictions for micellization of these model macromolecular systems.
| Richetti, P., Anthony, O., In, M., Marques, C., & Zana, R. (1997). Surface forces in oligomeric surfactant solutions. In Abstracts Of Papers Of The American Chemical Society (Vol. 213, 272-COLL).|
| Yaman, K., Jeng, M., Pincus, P., Jeppesen, C., & Marques, C. M. (1997). Rods near curved surfaces and in curved boxes. Physica A, 247(1-4), 159–182.|
Abstract: We consider an ideal gas of infinitely rigid rods near a perfectly repulsive wall, and show that the interfacial tension of a surface with rods on one side is lower when the surface bends towards the rods. Surprisingly we find that rods on both sides of surfaces also lower the energy when the surface bends. We compute the partition functions of rods confined to spherical and cylindrical open shells, and conclude that spherical shells repel rods, whereas cylindrical shells (for thickness of the shell on the order of the rod-length) attract them. The role of flexibility is investigated by considering chains composed of two rigid segments.
Keywords: colloids; depletion; rod solutions; membranes
| Yaman, K., Pincus, P., & Marques, C. M. (1997). Membranes in rod solutions: A system with spontaneously broken symmetry. Phys. Rev. Lett., 78(23), 4514–4517.|
Abstract: We consider a dilute solution of infinitely rigid rods near a curved, perfectly repulsive surface and study the contribution of the rod depletion layer to the bending elastic constants of membranes. We find that a spontaneous curvature state can be induced by exposure of both sides of the membrane to a rod solution. A similar result applies for rigid disks with a diameter equal to the rod's length. We also study the confinement of rods in spherical and cylindrical repulsive shells. This helps elucidate a recent discussion on curvature effects in confined quantum mechanical and polymer systems.
| Marques, C. M., & Fournier, J. B. (1996). Deviatoric spontaneous curvature of lipid membranes induced by Siamese macromolecular cosurfactants. Europhysics Lett., 35(5), 361–365.|
Abstract: We study the anisotropy of the spontaneous curvature induced by a membrane inclusion consisting of two geminated polymer-lipid molecules. The anisotropy is found to be of the order of the mean spontaneous curvature. Such a strong anisotropy yields a significant reduction of the membrane bending rigidity K as well as an increase of the saddle splay (K) over bar, which might lead to curvature instabilities.
| Sens, P., Marques, C. M., & Joanny, J. F. (1996). Mixed micelles in a bidisperse solution of diblock copolymers. Macromolecules, 29(14), 4880–4890.|
Abstract: This paper discusses theoretically the formation of micelles in a bidisperse solution of diblock copolymers. The two populations of copolymer chains are of identical chemical nature but have otherwise arbitrary different block asymmetries. We find that these asymmetries, or correspondingly the relative ratios of curvature of the diblocks, determine the micellization scenario and the type of aggregates coexisting in solution. If the asymmetries between the sizes of the blocks of the two copolymers are not too large, the short copolymers are incorporated continuously in the large copolymer micelles and only mixed micelles are stable. If the asymmetries are larger, the mixed micelles always contain a finite number of short copolymer chains; mixed micelles and large copolymer micelles can then coexist.
| Jones, J., Marques, C., & Joanny, J. (1995). Shear-Induced Micellization Of Diblock Copolymers. Macromolecules, 28(1), 136–142.|
Abstract: The influence of a weak shear flow on the micellization of diblock copolymers in selective solvents is investigated. The micelles are described as small microgel beads and the hydrodynamic fields calculated within the Brinkman approximation. The critical micellar concentration is shown to decrease in the shear flow, leading to the possibility of shear-induced micellization. It is also shown that the aggregation number of the micelles is modified by the flow: it increases for micelles with a large asymmetry but decreases for more symmetric micelles.
| Schmitt, V., Marques, C., & Lequeux, F. (1995). Shear-Induced Phase-Separation Of Complex Fluids – The Role Of Flow-Concentration Coupling. Physical Review E, 52(4), 4009–4015.|
Abstract: We propose a classification scheme for the instabilities that might arise in sheared complex fluids. A central role is played by the coupling between the flow and the solute concentration, which is a combination of the parameters describing (a) the tendency of solute molecules to migrate to regions of small or high shear rates and (b) the variation of the viscosity with concentration. Using a mean field approach, we show that the nature and the geometry of the instability can be predicted from the knowledge of the coupling parameter, the diffusion coefficient, and the derivative of the stress with respect to the shear rate. We also successfully compare a description of the variation of the stress at and just beyond the instability threshold, with experimental results from a wormlike surfactant solution of CPClO3.
| Turner, M., & Marques, C. (1995). Embedding Of Colloids In Copolymer Cubic Phases – An Impurity Stabilized Crystal. Europhysics Lett., 32(6), 493–497.|
Abstract: We discuss the possibility of embedding colloidal solid particles in a cubic crystal of diblock copolymers. We show that the solubility of the colloids in the cores of the minority phase is enhanced, for a certain range of the particle radius, by the release of elastic tension of the polymer chains. This provides an explicit example for elastically assisted solubilization of Spherical inclusions in a crystal.
| Marques, C., Turner, M., & Cates, M. (1994). Relaxation Mechanisms In Worm-Like Micelles. Journal Of Non-Crystalline Solids, 172, 1168–1172.|
Abstract: Aqueous solutions of surfactants such as CTAC/NaSal and CTAB/KBr, certain dye molecules, S-8 rings in plastic sulphur or the alpha form of polymethylstyrene are thought to self-assemble reversibly into long, linear flexible chains. The fascinating properties of these systems arise from their propensity to randomly destroy or create connections between chains, a labile character which allows for exchange of material from chain to chain. As a consequence they exhibit a unique dynamic behaviour, which reflects both the kinetics of exchange of material from chain to chain and the dynamic properties of polymers. In this paper four types of reaction that have been proposed as candidates for describing the kinetics in these systems are reviewed. The implications of these mechanisms on the viscoelastic behaviour of the living polymer materials are also discussed.
| Sens, P., Marques, C., & Joanny, J. (1994). Viscoelasticity Of Adsorbed Polymer Layers. Macromolecules, 27(14), 3812–3820.|
Abstract: We discuss theoretically dynamic measurements with a surface force apparatus composed of a plane and a sphere coated with adsorbed polymer layers in a good solvent. The hydrodynamics are studied within a simple two fluids model where the friction between polymer and solvent is described by the so-called Brinkman approximation. In a steady compression experiment the distance between the sphere and the plane varies at a constant velocity and the polymer layers have a hydrodynamic thickness e(H) of the order of their radius of gyration. In a periodic compression experiment, the distance has a periodic modulation of small amplitude at a finite frequency; the results are recast in terms of a complex modulus G. At a low frequency, the modulus has the standard Maxwell behavior (G' congruent-to omega2, G'' congruent-to omega). The contribution of the polymer to the loss modulus G'' is small when the polymer layers do not overlap; it is of the same order of magnitude as the pure solvent contribution when they do overlap. The elastic modulus increases with the thickness of the adsorbed layers. At a high frequency, the complex modulus increases as G congruent-to omega2/3 and is independent of the thickness of the polymer layers. When the adsorbed polymer layers overlap, there is an intermediate regime where the elastic part of the modulus increases as G' congruent-to omega4/3.
| Turner, M., Rubinstein, M., & Marques, C. (1994). Surface-Induced Lamellar Ordering In A Hexagonal Phase Of Diblock Copolymers. Macromolecules, 27(18), 4986–4992.|
Abstract: We study theoretically the hexagonal phase of diblock copolymer melts and determine the conditions under which a region of lamellar ordering is induced near a flat surface. In the weak segregation limit we employ a Landau-Ginzburg mean-field theory to describe the interfacial structure of the ordered hexagonal phase. The surface field, proportional to the differential affinity of blocks A and B to the surface, couples to the wave component perpendicular to the interface and increases the lamellar character of the ordered structure close to the surface. The extent of the region where this lamellar character predominates diverges logarithmically when the hulk hexagonal-lamellar transition is approached. In the strong segregation limit we find that the lamellar region exists provided that the surface field is larger than some critical value, readily obtainable in experiments. We find that the extent of the region of lamellar ordering also increases logarithmically with decreasing free energy difference between the hexagonal and lamellar phases.
| Izzo, D., & Marques, C. (1993). Formation Of Micelles Of Diblock And Triblock Copolymers In A Selective Solvent. Macromolecules, 26(26), 7189–7194.|
Abstract: We study theoretically the formation of dilute phases of spherical (micelles), cylindrical (vermicelles), and planar (lamellae) aggregates of copolymer chains in a selective solvent. In the case of diblock copolymer chains, micelles are formed for all values of the block asymmetry in the regime where dilute phases are predicted to occur (N(A) much less than N(B)3/2, with N(A) and N(B) the polymerization indices of the A-collapsed and B-swollen blocks). For B-A-B triblock copolymers we find that spherical or cylindrical hollow structures might exist in the solvent in a metastable state with a long associated lifetime.
| Marko, J., Johner, A., & Marques, C. (1993). Grafted Polymers Under The Influence Of External Fields. Journal Of Chemical Physics, 99(10), 8142–8153.|
Abstract: The structure of grafted polymer ''brushes'' may be profoundly modified by the action of ''external fields''-local shifts in chemical potential due to, e.g., interfacial effects at the grafting surface. We discuss the strong-stretching limit of the self-consistent mean-field theory for a brush exposed to an arbitrary external potential, a simple scaling law for the brush height arises in the case where the external field pushes monomers towards the surface. In contrast, repulsive interactions can lead to ''exclusion zones'' or regions from which polymer ends are repelled, leading to a breakdown of the simple scaling formula. We exactly solve the self-consistent theory of the brush in a repulsive square well where an exclusion zone always appears. Our results describe a brush in the case where a thin layer of one component of a binary solvent that is a worse solvent for the polymer than is the bulk mixture wets the grafting surface. We also discuss the effects of thermal fluctuations and chain polydispersity on our results, and estimate the effects of various interfacial phenomena on the brush structure.
| Marques, C. (1993). Fluctuation Effects In The Ordering Of Thin Diblock Copolymer Films. Physical Review Letters, 70(9), 1351.|
| Marques, C., Turner, M., & Cates, M. (1993). End-Evaporation Kinetics In Living-Polymer Systems. Journal Of Chemical Physics, 99(9), 7260–7266.|
Abstract: We study theoretically the process of ''end-evaporation'' in living polymer systems, such as wormlike surfactant micelles. End-evaporation occurs when single monomers either break away from, or join onto, a chain end, the rates being described by the (mean-field) rate constants k and k', respectively. Thus the chains can exchange material with one-another via a bath of free monomers. The relaxation of a system of living polymers after a small temperature jump (T-jump) is studied theoretically. The effect of a T-jump is to prepare the system with the wrong mean chain length, which relaxes to its equilibrium value LBAR by end-evaporation. It is found that the number of free monomers in the system relaxes almost completely in a time of order 1/kLBAR, while the weight-average chain length, which is the quantity measured in light scattering experiments, relaxes on a time scale tau(D) = 4 L2BAR/k, which is three powers of L longer. We also predict that the stress relaxation after a step strain is dominated by end-evaporation whenever tau(D) less than or similar tau(rep), where tau(rep) is the reptation (disengagement) time for a chain of length L. In this case the stress relaxation is found to be ''stretched exponential'' for times smaller than tau(D) and single exponential for longer times.
| Schmitt, V., Lequeux, F., & Marques, C. (1993). Confinement Of Dilute-Solutions Of Living Polymers. Journal De Physique Ii, 3(6), 891–902.|
Abstract: We investigate the thermodynamic properties of a dilute solution of living polymers confined between two solid repulsive walls. We consider both the case of rigid and of flexible macromolecules. When the confined system is taken to be at equilibrium with an external reservoir the living polymers behave similarly to a polydisperse solution of unbreakable chains. However for closed gaps the behaviour is quite different from a classical polymer solution because the worm-like micelles can adapt their intrinsic polydispersity in order to release the confinement constraint. In particular, for rigid living polymers this leads to a divergence of the average chain-length in the limit of strong confinement, as well as to a non-monotonic behaviour of the pressure acting on the walls.
| Sens, P., Marques, C., & Joanny, J. (1993). Hydrodynamic Modes Of Viscoelastic Soap Films. Langmuir, 9(11), 3212–3218.|
Abstract: We discuss the dispersion relation of the undulation modes of a soap film containing a viscoelastic Maxwell fluid modeling a water soluble polymer. Two types of modes exist, bending modes and squeezing modes. In addition to the modes existing for a usual viscous soap film, we find Rayleigh waves driven by the bulk elasticity E of the liquid. The dispersion relation of the undulation modes strongly depends on the value of the surface elastic modulus of the surfactant layers epsilon(s). We study in detail the limit where the surface elastic modulus vanishes and the limit where it is of the same order of magnitude as the surface tension. In this last case the Rayleigh waves are observed if Eh >> epsilon(s) where h is the thickness of the film. We also discuss briefly the existence of higher harmonics due to the coupling of the undulation modes to compressional elastic modes of the film.
| Turner, M., Marques, C., & Cates, M. (1993). Dynamics Of Wormlike Micelles – The Bond-Interchange Reaction Scheme. Langmuir, 9(3), 695–701.|
Abstract: We study theoretically the dynamics of systems of elongated wormlike micelles which undergo ''bond-interchange'' reactions. Bond-interchange reactions may occur when two micelles come into contact at some point along their arc lengths. A transient structure resembling a four-armed star polymer is formed briefly, decaying to give two new micelles with each section of the first micelle fusing to one or other section of the second. First we consider the relaxation of the molecular weight distribution (MWD) of a system of wormlike micelles after an arbitrary (material conserving) perturbation to the MWD. We show that bond-interchange reactions do not provide a pathway for the relaxation of the MWD to equilibrium. Second we consider the dynamics of entangled systems of wormlike micelles. We calculate the scaling of the terminal time, viscosity, and monomer diffusion constant with the volume fraction of surfactant in the regime where micellar reactions are rapid on the time scale of reptation. These results may help in identifying systems in which bond-interchange reactions occur. Finally we discuss the validity of the ''tube'' model in these systems. We consider when a description based on the tube model is appropriate, given that bond-interchange reactions allow chains to pass through one another.
| Harden, J., Marques, C., Joanny, J., & Andelman, D. (1992). Membrane Curvature Elasticity In Weakly Charged Lamellar Phases. Langmuir, 8(4), 1170–1175.|
Abstract: We study the effect of electrostatic interactions on the membrane bending energies of weakly charged, swollen, lamellar phases of surfactant solutions. We treat the surface charge density of the lamellae as a constant and consider only situations where it is low enough so that the distance 2d between lamellae is the smallest relevant length scale in the problem. In the presence of salt (the short-distance Debye-Huckel regime) we show that the electrostatic contribution to the bending energy of a membrane is in general small, in disagreement with a previous result, is proportional to d3, and is independent of ionic strength. Identical results are obtained for membranes undulating sinusoidally in phase and for concentric cylindrical membranes. The bending constant is also calculated for membranes held at constant electric potential and is compared to the constant charge density case. In the absence of salt, continuity arguments predict an electrostatic contribution to the bending energy that scales as d3. Furthermore, a direct calculation for concentric cylindrical membranes gives exactly the same scaling behavior (including the numerical prefactor) as in the presence of salt.
| Johner, A., & Marques, C. (1992). Can A Polymer Brush Trap A Wetting Layer. Physical Review Letters, 69(12), 1827–1830.|
Abstract: Grafted polymer layers are well known as stabilizing agents in colloial dispersions. Here we show how these polymer “brushes” may also deeply modify wetting phenomena by favoring the formation of stable wetting layers of microscopic size. We discuss in particular the influence of a solvated polymer layer on the wetting properties of the substrate by a second minority solvent. In the case where the brush prefers the second solvent, this solvent may be drawn to the interface even if it would not ordinarily wet the substrate. On the contrary, a solvent that ordinarily forms a thick wetting layer may be partially inhibited from doing so (forming a thin trapped layer) if it is a worse solvent for the brush.
| Rivory, J., Frigerio, J., & Marques, C. (1992). Characterization Of Interfacial Index Gradients By Spectroscopic Ellipsometry At Variable Angle Of Incidence. Optics Communications, 89(5-6), 482–492.|
Abstract: We discuss the characterization of inhomogeneous thin films by ellipsometry. We compare the sensitivity of ellipsometry measurements for different configurations – chromium mirror, total reflection prism and surface plasmon excitation – taking as an example the refractive index gradient of a polymer grafted layer. For thin layers (with a thickness much smaller than the wave-length), it is rather difficult in any configuration to analyze the details of the refractive index profile by a direct examination of the ellipsometric parameters. We thus propose an alternative treatment of the measured quantities, based upon the angular dependence of the effective thickness and refractive index of the inhomogeneous layer, calculated in the framework of the linear Born approximation.
| Brooks, J., Marques, C., & Cates, M. (1991). Role Of Adsorbed Polymer In Bilayer Elasticity. Europhysics Lett., 14(7), 713–718.|
Abstract: We study theoretically the effect of adsorbed homopolymer on surfactant bilayers. We formulate the energy of adsorption per unit area as a Taylor series in curvature for both spherical and cylindrical surfaces. In the limits of weak adsorption analytic expressions are derived for the polymeric contribution to the elastic moduli of the bilayer, using a scaling functional approach. For stronger adsorption numerical and asymptotic calculations have been made. In all cases the presence of the polymer leads to a decrease in the mean curvature rigidity K and an increase in the Gaussian rigidity KBAR. For strong adsorption these contributions are comparable to k(B)T; thus the presence of adsorbed polymer can strongly influence the elasticity of surfactant bilayers.
| Brooks, J., Marques, C., & Cates, M. (1991). The Effect Of Adsorbed Polymer On The Elastic-Moduli Of Surfactant Bilayers. Journal De Physique Ii, 1(6), 673–690.|
Abstract: We study theoretically the effect of adsorbed homopolymer on surfactant bilayers, restricting ourselves to homogeneous equilibrium adsorption of polymer on both sides of the bilayer, with no penetration. We formulate the energy of adsorption per unit area as a Taylor series in curvature for both spherical and cylindrical surfaces. In the limit of weak adsorption analytic expressions for the polymeric contribution to the mean and Gaussian elastic moduli of the bilayer are derived, using both a mean-field and a scaling functional approach. For stronger adsorption numerical calculations have been made, and in the limit of very strong adsorption, asymptotic functional forms for the elastic moduli found. In all cases the presence of the polymer leads to a decrease in the mean curvature rigidity K and an increase in the Gaussian rigidity KBAR. At the mean-field level these contributions are always small compared to the thermal energy k(B) T. However the scaling theory predicts qualitatively similar, but quantitatively larger effects; thus the presence of adsorbed polymer can strongly influence the elasticity of surfactant bilayers.
| Cates, M., & Marques, C. (1991). Shear Induced Order In Dilute Lamellar Systems. Phys. Scr., T35, 75–78.|
Abstract: Certain lyotropic surfactant systems, including microemulsions, form smectic phases at very low volume fractions of surfactant (in the few percent range). Upon further dilution these melt into an isotropic state. The effect of a steady shear flow on this transition has been considered from the point of view of time-dependent Landau Ginzburg theory. In the absence of a cubic term in the Landau expansion, the theory predicts, in a suitable temperature range, a transition from the isotropic to the lamellar phase at a critical shear rate D*. (Preliminary experiments suggest D* of only a few reciprocal seconds for certain highly diluted bilayer-forming surfactant systems.) In the presence of a cubic term (as expected for most microemulsions, on symmetry grounds), there is the further possibility of an hexagonal phase. In this case we predict that the hexagonal phase is stabilized by shear even more effectively than the lamellar one. Hence we expect systems to exist for which hexagonal order is induced by a flow, whereas lowering the temperature produces a lamellar phase instead.
| Cates, M., Marques, C., & Bouchaud, J. (1991). Dynamic Relaxation Of Rodlike Micelles. Journal Of Chemical Physics, 94(12), 8529–8536.|
Abstract: We study theoretically the angular relaxation and translational diffusion of stiff rodlike micelles that can undergo reversible scission reactions, in both the dilute and the entangled regime. The very strong dependence of the angular diffusion constant on rod length leads to an anomalous superdiffusive behavior of the typical angular deflection of a subunit at short times. Despite this, angular correlation functions such as <u(t).u(O)> (also the linear birefringence and entropic stress response) decay exponentially with a relaxation time that is a power law combination of the time scales for reversible scission and for angular rotation of a (hypothetical) unbreakable rod. This relaxation time corresponds to the waiting time for a subunit to find itself on a rod that is short enough to rotate through an angle of order pi before recombining with another rod. The translational diffusion of rodlike micelles shows no anomaly in contrast to the angular case. However, the collective diffusion and self-diffusion constants differ by a factor of 2 at all concentration ranges for which rod micelles exist. The diffusion equation for collective motion is nonlinear (even below the overlap threshold) since the mobility of the rods depends on their local concentration. The dynamic structure factor S(q,t) is calculated to order q4, the quartic terms providing, in principle, a probe of the micellar scission time.
| Johner, A., Joanny, J., & Marques, C. (1991). Diblock Copolymers In Selective Solvents. Physica A, 172(1-2), 285–289.|
Abstract: We review our recent work on diblock copolymers in highly selective solvents. This includes the static and kinetic properties of micelles, the thermodynamic description of a copolymer layer adsorbed on a wall and the kinetics of formation of an adsorbed layer.
| Marques, C., & Cates, M. (1991). Nonlinear Thermodynamic Relaxation In Living Polymer Systems. Journal De Physique Ii, 1(5), 489–492.|
Abstract: We present the complete (nonlinear) solution for the response of a system of living polymers to an arbitrary thermodynamic perturbation of its equilibrium polymer size distribution. Our results are relevant for the interpretation of T-jump experiments on wormlike micelles in the concentrated regime, where very large perturbations to the equilibrium size distribution can be easily obtained.
| Marques, C., Frigerio, J., & Rivory, J. (1991). Effective Ellipsometric Thickness Of An Interfacial Layer. Journal Of The Optical Society Of America B-Optical Physics, 8(12), 2523–2528.|
Abstract: We calculate the effective ellipsometric thickness d and index of refraction delta-n of interfacial inhomogeneous layers. Exact formulas are derived in the limit of zero contrast for the two usual geometries in which the light travels toward the surface from the air-liquid medium or from the substrate. d and delta-n are in general functions of the incident vector q, and, for small-q values and a thin layer, these effective parameters follow a parabolic dependence in q, from which the first four moments of the layer profile can be obtained. We discuss the applicability of this method for different families of profiles. We also test its predictions against the effective thickness and refractive index obtained by the numerical integration of the Maxwell equations, for the parabolic profile describing a grafted layer of polymers.
| Shim, D., Marques, C., & Cates, M. (1991). Diblock Copolymers – Comicellization And Coadsorption. Macromolecules, 24(19), 5309–5314.|
Abstract: In this paper we study the conditions under which comicellization occurs for a bimodal distribution of diblock copolymers in a selective solvent. The formation of pure micelles or comicelles depends on the relative concentration of the two species of diblock copolymers in solution. Regions of pure micelles in equilibrium with the free chains belonging to the two species exist in the phase diagram at low concentrations of one or other species, but for high enough concentrations of both species, comicelles may be present depending on the interaction parameter of the bimodal core. We consider the effects of varying this interaction parameter. We also discuss the interfacial behavior of mixed copolymer systems, and the conditions under which monodisperse or bimodal “brushes” of adsorbed polymer will form on an attractive surface.
| Jones, J., & Marques, C. (1990). Rigid Polymer Network Models. Journal De Physique, 51(11), 1113–1127.|
| Marques, C., & Cates, M. (1990). Harmonic Corrections Near The Ordering Transition. Europhysics Lett., 13(3), 267–272.|
| Marques, C., & Cates, M. (1990). Hexagonal And Lamellar Mesophases Induced By Shear. Journal De Physique, 51(16), 1733–1747.|
| Marques, C., & Joanny, J. (1990). Adsorption Of Random Copolymers. Macromolecules, 23(1), 268–276.|
| Marques, C., & Joanny, J. (1989). Block Copolymer Adsorption In A Nonselective Solvent. Macromolecules, 22(3), 1454–1458.|
| Marques, C., & Joanny, J. (1988). Adsorption Of Semi-Dilute Polymer-Solutions On Fractal Colloidal Grains. Journal De Physique, 49(7), 1103–1109.|
| Marques, C., Joanny, J., & Leibler, L. (1988). Adsorption Of Block Copolymers In Selective Solvents. Macromolecules, 21(4), 1051–1059.|