| Weinberger, A., Walter, V., MacEwan, S. R., Schmatko, T., Muller, P., Schroder, A. P., et al. (2017). Cargo self-assembly rescues affinity of cell-penetrating peptides to lipid membranes. Sci Rep, 7, 43963.|
Abstract: Although cationic cell-penetrating peptides (CPPs) are able to bind to cell membranes, thus promoting cell internalization by active pathways, attachment of cargo molecules to CPPs invariably reduces their cellular uptake. We show here that CPP binding to lipid bilayers, a simple model of the cell membrane, can be recovered by designing cargo molecules that self-assemble into spherical micelles and increase the local interfacial density of CPP on the surface of the cargo. Experiments performed on model giant unilamellar vesicles under a confocal laser scanning microscope show that a family of thermally responsive elastin-like polypeptides that exhibit temperature-triggered micellization can promote temperature triggered attachment of the micelles to membranes, thus rescuing by self-assembly the cargo-induced loss of the CPP affinity to bio-membranes.
| Schmatko, T., Muller, P., & Maaloum, M. (2014). Surface charge effects on the 2D conformation of supercoiled DNA. Soft Matter, 10(15), 2520–2529.|
Abstract: We have adsorbed plasmid pUc19 DNA on a supported bilayer. By varying the fraction of cationic lipids in the membrane, we have tuned the surface charge. Plasmid conformations were imaged by Atomic Force Microscopy (AFM). We performed two sets of experiments: deposition from salt free solution on charged bilayers and deposition from salty solutions on neutral bilayers. Both sets show similar trends: at low surface charge density or low bulk salt concentration, the internal electrostatic repulsion forces plasmids to adopt completely opened structures, while at high surface charge density or higher bulk salt concentration, usual supercoiled plectonemes are observed. We experimentally demonstrate the equivalence of surface screening by mobile interfacial charges and bulk screening from salt ions. At low to medium screening, the electrostatic repulsion at plasmid crossings is predominant, leading to a number of crossovers decreasing linearly with the characteristic screening length. We compare our data with an analytical 2D-equilibrated model developed recently for the system and extract the DNA effective charge density when strands are adsorbed at the surface.
| Maaloum, M., Muller, P., & Harlepp, S. (2013). DNA-intercalator interactions: structural and physical analysis using atomic force microscopy in solution. Soft Matter, 9(47), 11233–11240.|
Abstract: DNA has a strong affinity for many heterocyclic aromatic dyes, such as acridine and its derivatives. Lerman in 1961 first proposed intercalation as the source of this affinity, and this mode of DNA binding has since attracted considerable research scrutiny. DNA intercalators (molecules that intercalate between DNA base pairs) have attracted particular attention due to their antitumoral activity and because they are widely used to fluorescently label DNA. The interaction between double-stranded DNA and bis-intercalators, such as the fluorescent dye YOYO-1 (dimer of oxazole yellow), has been widely studied. In the literature, there are contradicting data regarding the structure and the rigidity of the complex DNA-YOYO-1. Here, we address this problem using high-resolution atomic force microscopy in solution. We directly measured important structural parameters, such as the helical pitch and the elongation of the complex. By measuring intercalator-induced DNA elongation at different YOYO-1 concentrations, we determined the binding constant. We showed that intercalation induces distinct changes in the molecular elasticity compared to the free double stranded DNA. We found a decrease of the persistence length of DNA with increasing amount of bound YOYO-1, which contrasts with some previous assumptions. This study helps in understanding the physicochemical properties of bis-intercalators as well as the mechanism by which they interact with DNA and this technique can ultimately be applied to a large range of other DNA binding molecules such as anti-cancer or anti-viral drugs.
| Lee, N. - K., Schmatko, T., Muller, P., Maaloum, M., & Johner, A. (2012). Shape of adsorbed supercoiled plasmids: an equilibrium description. Phys Rev E Stat Nonlin Soft Matter Phys, 85(5 Pt 1), 051804.|
Abstract: Inspired by recent atomic force microscope (AFM) images of plasmids deposited on oppositely charged supported lipid bilayers from salt free solution, we propose a model for strongly adsorbed supercoiled cyclic stiff polyelectrolytes. We discuss how the excess linking number Lk of the deposited cycle is shared between writhe Wr and twist Tw at equilibrium and obtain the typical number of self-crossings in the deposited cycle as a function of surface charge density. The number of crossings at equilibrium is simply determined by the crossing penalty which is a local quantity and by the excess linking number. The number of crossings is well defined despite versatile plasmid shapes. For moderate numbers of crossings the loops are rather small and localized along the primary cycle, as expected from entropic loops. In the regime of many crossings, the cycle takes the shape of a regular flat ply ruled by local stiffness. The model allows for a semiquantitative comparison with the AFM images of deposited plasmids which are strongly charged.
Keywords: Adsorption; DNA, Superhelical/*chemistry; Models, Molecular; Plasmids/*chemistry; Surface Properties
| Qi, L., Fresnais, J., Muller, P., Theodoly, O., Berret, J. F., & Chapel, J. P. (2012). Interfacial Activity of Phosphonated-PEG Functionalized Cerium Oxide Nanoparticles. Langmuir, 28(31), 11448–11456.|
Abstract: In a recent publication, we have highlighted the potential of phosphonic acid terminated PEG oligomers to functionalize strong UV absorption cerium oxide nanoparticles,(1) which yield suspensions that are stable in aqueous or organic solvents and are redispersible in different solvents after freeze-drying. In the present work, we highlight the interfacial activity of the functional ceria nanoparticles and their potential to modify hydrophobic surfaces. We first investigated the phosphonated-PEG amphiphilic oligomers behavior as strong surface active species forming irreversibly adsorbed layers. We then show that the oligomers interfacial properties translate to the functional nanoparticles. In particular, the addition of a small fraction of phosphonated-PEG oligomers with an extra C16 aliphatic chain (stickers) into the formulation enabled the tuning of (i) the nanoparticles adsorption at the air/water, polystyrene/water, oil/water interfaces and (ii) the particle/particle interaction in aqueous solutions. We also found that dense and closely packed two-dimensional monolayers of nanoceria can be formed by spontaneous adsorption or surface compression using a Langmuir trough. A hexagonal organization controlled by reversible and repulsive interaction has been characterized by GISAXS. Mono- or rnultilayers can also be stably formed or transferred on solid surfaces. Our results are key features in the field of polymer surface modification, solid-stabilized emulsions (Pickering), or supracolloidal assemblies.
| Maaloum, M., Beker, A. F., & Muller, P. (2011). Secondary structure of double-stranded DNA under stretching: Elucidation of the stretched form. Physical Review E, 83(3).|
Abstract: Almost two decades ago, measurements of force versus extension on isolated double-stranded DNA molecules revealed a force plateau. This unusual stretching phenomenon in DNA suggests that the long molecules may be extended from the usual B form into a new conformation. Different models have been proposed to describe the nature of DNA in its stretched form, S-DNA. Using atomic force microscopy combined with a molecular combing method, we identified the structure of lambda-phage DNA for different stretching values. We provide strong evidence for the existence of a first-order transition between B form and S form. Beyond a certain extension of the natural length, DNA molecules adopt a new double-helix conformation characterized by a diameter of 1.2 nm and a helical pitch of 18 nm.
| Mantelli, S., Muller, P., Harlepp, S., & Maaloum, M. (2011). Conformational analysis and estimation of the persistence length of DNA using atomic force microscopy in solution. Soft Matter, 7(7), 3412–3416.|
Abstract: The worm-like chain model describes the mechanical properties of semi-flexible polymers by introducing a certain correlation length along the contour. This correlation length is called the persistence length. Using atomic force microscopy in solution, we performed measurements of the persistence length of DNA molecules. We found good agreement between the theoretical model and experimental data. However, the measured persistence length values in solution differ from those found by several authors using the same technique but in dry air. In order to determine the contribution of the electrostatic persistence length to the total persistence length, we varied the salt concentration. We found a large discrepancy between the Odijk, Skolnick and Fixman theory and our measurements. The effect of divalent ions and the omission in the theory of the dependence of non-electrostatic persistence length on salt concentration are qualitatively invoked.
| Jacquin, M., Muller, P., Cottet, H., & Theodoly, O. (2010). Self-Assembly of Charged Amphiphilic Diblock Copolymers with Insoluble Blocks of Decreasing Hydrophobicity: From Kinetically Frozen Colloids to Macrosurfactants. Langmuir, 26(24), 18681–18693.|
Abstract: We have investigated the self-assembly properties in aqueous solution of amphiphilic diblock copolymers with insoluble blocks of different hydrophobicity and demonstrated that the condition to obtain dynamic micelles is to design samples with insoluble blocks of low enough hydrophobicity. We focus here on results with new water-soluble amphiphilic diblock copolymers poly(diethyleneglycol ethylether acrylate)-b-poly(acrylic acid), or PDEGA-b-PAA. The physical characteristics of PDEGA-b-PAA micelles at high ionization have been determined by small angle neutron scattering (SANS). We show that PDEGA-b-PAA samples form micelles at thermodynamic equilibrium. The critical micelle concentrations (CMCs) decrease strongly with ionic strength and temperature due to a solvent quality decrease for, respectively, the corona and the core. This behavior of reversible aggregation is remarkable as compared to the behavior of kinetically frozen aggregation that has been widely observed with samples of similar architecture and different hydrophobic blocks, for example, poly(styrene)-b-poly(acrylic acid), PS-b-PAA, and poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA. We have measured the interfacial tension between water and the homopolymers PDEGA and PBA at, respectively, 3 and 20 mN/m at room temperature, which permits one to estimate the energy cost to extract a unimer from a micelle. The results are consistent with a micelle association that is fast for PDEGA-b-PAA and kinetically frozen PBA-b-PAA. Hence, PDEGA-b-PAA samples form a new system of synthetic charged macro-surfactant with unique properties of fast dynamic association, tunable charge, and water solubility even at temperatures and NaCl concentrations as high as 65 degrees C and 1 M.
| Theodoly, O., Checco, A., & Muller, P. (2010). Charged diblock copolymers at interfaces: Micelle dissociation upon compression. Europhysics Lett., 90(2), 6 pp.|
Abstract: We use grazing incidence X-ray scattering to study the surface micellization of charged amphiphilic diblock copolymers poly(styrene-block-acrylic acid) at the air-water interface. Scattering interference peaks are consistent with the formation of hexagonally packed micelles. The remarkable increase of inter-micelle distance upon compression is explained by a dissociation of micelles into a brush. Hence, surface micelles reorganize, whereas micelles of the same copolymers in solutions are “frozen”. We show indeed that the energetic cost of unimer extraction from micelles is much lower for surface than for solution. Finally, a model combining electrostatic interactions and micelle/brush equilibrium explains surface pressure vs. area without free parameters. Copyright (C) EPLA, 2010
| Charrault, E., He, M. S., Muller, P., Maaloum, M., Petit, C., & Petit, P. (2009). A Facile Route to Homogeneous High Density Networks of Metal Nanoparticles. Langmuir, 25(19), 11285–11288.|
Abstract: In this communication, we report an inexpensive and simple-to-implement method using self-assembly properties of surfactants onto solid substrates for patterning square centimeter surfaces with a high density of catalyst metal nanoparticles with narrow size distributions. This method, which uses patterns of hemimicelles of partially fluorinated alkanes as masks and over metal evaporation, leads to typical particle sizes and spacings of 2 and 25 nm, respectively, arranged in a hexagonal network with a density of about 10(11) particles/cm(2). Using gold as the metal, we show the ability of such material to catalyze the oxidation reaction of carbon monoxide into carbon dioxide at low temperature.
| Theodoly, O., Jacquin, M., Muller, P., & Chhun, S. (2009). Adsorption Kinetics of Amphiphilic Diblock Copolymers: From Kinetically Frozen Colloids to Macrosurfactants. Langmuir, 25(2), 781–793.|
Abstract: We investigated the spontaneous adsorption properties of charged amphiphilic diblock copolymers on hydrophobic surfaces and explained the transition of behavior from depleting frozen colloids (that do not adsorb at all) to fast adsorbing macrosurfactants when the hydrophobicity of the nonsoluble block is reduced. Three copolymer families have been used with the same hydrophilic block poly(acrylic acid), a weak acid whose ionization (x can be varied by changing the pH. The hydrophobic blocks polystyrene, PS, poly(n-butyl acrylate), PBA, and poly(diethylene glycol ethyl ether acrylate), PDEGA, have interfacial tensions with water Y-core/solvent, respectively, of 32, 20, and 3 mN/m. We were mainly interested in the regime of high ionization alpha > 0.3, where PAA chains have no affinity for hydrophobic surfaces, and we verified experimentally that micelles do not adsorb directly. With the three copolymer families we show that the adsorption kinetics at an early stage is driven by the self-assembly properties in bulk Solution: adsorption is hampered for PS-b-PAA (physically/kinetically frozen micelles in solution), controlled by unimer extraction for PBA-b-PAA (nonequilibrium micelles in solution with very low CMC < 10(-4) wt %), and controlled by unimer diffusion and electrostatic repulsion for PDEGA-b-PAA (micelles at equilibrium in solution with high CMC approximate to 1-5 wt %). This explains the power law dependences of adsorption with concentration as C-1 for PBA-b-PAA and C-2 for PDEGA-b-PAA. It is finally the interfacial tension with water of the nonsoluble block and not its glass transition that is the main control of bulk solution self-assembly and consequently of the adsorption kinetics properties of amphiphilic diblocks. We also proved by preparative GPC that the fraction of non-self-assembling diblock chains, which exists in all highly hydrophobic amphiphilic diblock systems, plays a negligible role in the adsorption properties. Finally, we investigated the intrinsic thermodynamic affinity between amphiphilic diblocks and hydrophobic surfaces. We show quantitatively that this affinity depends dominantly on the interfacial energies between the hydrophobic block, the surface, and water: diblocks with strongly hydrophobic nonsoluble blocks (PS, PBA) have a low affinity for weakly hydrophobic surfaces, and oppositely, diblocks with weakly hydrophobic nonsoluble block (PDEGA) have a universal affinity for hydrophobic surfaces (like small-molecule surfactants, but for different physical reasons). Finally, we showed via Surface rheology that when adsorption occurs anchoring is strong and irreversible for very hydrophobic diblocks (PBA-b-PAA) and weaker and (partially) reversible for less hydrophobic diblocks (PDEGA-b-PAA).
| Muller, P., Sudre, G., & Theodoly, O. (2008). Wetting transition on hydrophobic surfaces covered by polyelectrolyte brushes. Langmuir, 24(17), 9541–9550.|
Abstract: We study the wetting by water of complex “hydropliobic-hydrophilic” Surfaces made of a hydrophobic substrate covered by a hydrophilic polymer brush. Polystyrene (PS) substrates covered with polystyrene-block-poly(acrylic acid) PS-b-PAA diblock copolymer layers were fabricated by Langmuir-Schaefer depositions and analyzed by atomic force microscopy (AFM) and ellipsometry. On bare PS Substrate, we measured advancing angles theta(A) = 93 +/- 1 degrees and receding angles theta(R) = 81 +/- 1 degrees. On PS covered with poorly anchored PS-b-PAA layers, we observed large contact angle hysteresis, theta(A) approximate to 90 degrees and theta(R) approximate to 0 degrees, that we attributed to nanometric scale dewetting of the PS-b-PAA layers. On well-anchored PS-b-PAA layers that form homogeneous PAA brushes, a wetting transition from partial to total wetting occurs versus the amount deposited: both OA and OR decrease close to zero. A model is proposed, based on the Young-Dupre equation, that takes into account the interfacial pressure of the brush Pi, which was determined experimentally, and the free energy of hydration of the polyelectrolyte monomers Delta G(PAA)(hyd), which is the only fitting parameter. With Delta G(PAA)(hyd) approximate to -1300 J/mol, the model renders the wetting transition for all samples and explains why the wetting transition depends mainly oil the average thickness of the brush and weakly oil the length of PAA chains.
| Jacquin, M., Muller, P., Cottet, H., Crooks, R., & Theodoly, O. (2007). Controlling the melting of kinetically frozen poly(butyl acrylate-b-acrylic acid) micelles via addition of surfactant. Langmuir, 23, 9939–9948.|
Abstract: We have studied the melting of polymeric amphiphilic micelles induced by small-molecule surfactant and explained the results by experimental determination of the interfacial tension between the core of the micelles and the surfactant solutions. Poly(n-butyl acrylate-b-acrylic acid) (PBA-b-PAA) amphiphilic diblock copolymers form kinetically frozen micelles in aqueous solutions. Strong interactions with surfactants, either neutral or anionic [C12E6, C6E4, sodium dodecyl sulfate (SDS)], were revealed by critical micelle concentration (cmc) shifts in specific electrode and surface tension measurements. Since both polymer and surfactant are either neutral or bear negative charges, the attractive interactions are not due to electrostatic interactions. Light scattering, neutron scattering, and capillary electrophoresis experiments showed important structural changes in mixed PBA-b-PAA/surfactant systems. Kinetically frozen micelles of PBA-b-PAA, that are hardly perturbed by concentration, ionization, ionic strength, and temperature stresses, can be disintegrated by addition of small-molecule surfactants. The interfacial energy of the PBA in surfactant solutions was measured by drop shape analysis with h-PBA homopolymer drops immersed in small-molecule surfactant solutions. The PBA/water interfacial energy gamma PBA/H2O of 20 mN/m induces a high energy cost for the extraction of unimers from micelles so that PBA-b-PAA micelles are kinetically frozen. Small-molecule surfactants can reduce the interfacial energy gamma PBA/Solution to 5 mN/m. This induces a shift of the micelle-unimer equilibrium toward unimers and leads, in some cases, to the apparent disintegration of PBA-b-PAA micelles. Before total disintegration, polymer/surfactant mixtures are dispersions of polydisperse mixed micelles. Based on core interfacial energy arguments, the disintegration of kinetically frozen polymeric micelles was interpreted by gradual fractionation of objects (polydisperse dispersion mechanism), whereas the disintegration of polymeric micelles in a thermodynamically stable state was interpreted by an exchange between a population of large polymer-rich micelles and a population of small surfactant-rich micelles (bidisperse dispersion mechanism). Finally, in our system and other systems from the literature, interfacial energy arguments could explain why the disintegration of polymer micelles is either partial or total as a function of the surfactant type and concentration and the hydrophobic block molar mass of the polymer.
| Jacquin, M., Muller, P., Lizarraga, G., Bauer, C., Cottet, H., & Theodoly, O. (2007). Characterization of amphiphilic diblock copolymers synthesized by MADIX polymerization process. Macromolecules, 40(8), 2672–2682.|
Abstract: We combined several analytical techniques (NMR, matrix assisted laser desorption ionization – time-of-flight mass spectroscopy MALDI-TOF MS, GPC, functional analysis on the first block, liquid chromatography at the point of exclusion adsorption transition LC-PEAT, and capillary electrophoresis CE) to analyze and quantify the characteristics of homopolymer precursors and amphiphilic diblocks synthesized by controlled radical polymerization process (CRP). We present here a detailed quantitative characterization of amphiphilic diblock copolymers (poly(butyl acrylate)-poly(acrylic acid) or PBA-b-PAA, and poly(di(ethylene glycol) ethyl ether acrylate)-poly(acrylic acid) or PDEGA-b-PAA). The samples were synthesized in ethanol by macromolecular design via inter-exchange of xanthate (MADIX), a reversible addition fragmentation transfer (RAFT) polymerization process using xanthates as control agents. The analytical results have permitted a determination of the transfer constant of xanthate C-Xa (approximate to 2.7 and 1.5 for respectively PBA and PDEGA) and the transfer constant to solvent C-s (approximate to 6 x 10(-4)). In the final diblock products, homopolymer side products were characterized. The amount of hydrophobic homopolymer was quantified by a specially developed LCPEAT technique in critical conditions for PBA. The hydrophilic homopolymer h-PAA amount was determined by quantitative capillary electrophoresis CE experiments. These analytical approaches allowed the quantification of the side products in a CRP system as well as the improvement of the reaction conditions via a thorough knowledge of the reaction mechanism.
| Jacquin, M., Muller, P., Talingting-Pabalan, R., Cottet, H., Berret, J. F., Futterer, T., et al. (2007). Chemical analysis and aqueous solution properties of charged amphiphilic block copolymers PBA-b-PAA synthesized by MADIX((c)). Journal Of Colloid And Interface Science, 316, 897–911.|
Abstract: We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)b-poly(acrylic acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameter chi(PBA/PAA), determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by liquid chromatography at the point of exclusion and adsorption transition, LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA-b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur. (C) 2007 Elsevier Inc. All rights reserved.
| Fontaine, P., Goldmann, M., Muller, P., Faure, M. C., Konovalov, O., & Krafft, M. P. (2005). Direct evidence for highly organized networks of circular surface micelles of surfactant at the air-water interface. Journal Of The American Chemical Society, 127(2), 512–513.|| |
| Zhang, G. F., Marie, P., Maalourn, M., Muller, P., Benoit, N., & Krafft, M. P. (2005). Occurrence, shape, and dimensions of large surface hemimicelles made of semifluorinated alkanes. elongated versus circular hemimicelles. Pit- and tip-centered hemimicelles. Journal Of The American Chemical Society, 127(29), 10412–10419.|
Abstract: The formation of large (similar to 20-35 nm) surface hemimicelles in monolayers of sernifluorinated alkanes, CnF2n+1CmH2m+1 (FnHm), observed after transfer onto silicon wafers, is a general phenomenon. F6H16 and F8H14 exclusively form highly monodisperse circular hemimicelles, organized in a hexagonal array. The other FnHm investigated form both circular and elongated hemimicelles. The longer FnHm is, the larger the area fraction of elongated micelles; both the hydrocarbon block (H-block) and the fluorocarbon block (F-block) affect this area fraction. The length of the elongated micelles increases with the total length of the diblocks. The diameter of the circular micelles increases with the length of the H-block but, unexpectedly, not with that of the F-block. Model calculations account for these observations. Close examination of the circular micelles showed that they generally present a pit or a tip at their center. The width of the elongated micelles is comparable to the radius of the circular micelles, suggesting that the latter arise from a partition of elongated micelles, followed by coalescence of the edges of the resulting fragments. The elongated micelles become shorter and fewer when surface pressure increases, further suggesting a conversion of elongated into circular micelles. This conversion is reversible. The surface pressure-molecular area isotherms do not present any feature that forebears the existence of hemimicelles. The obtaining of stable surface patterns from simple, “nonpolar” molecular fluorocarbon/hydrocarbon diblocks opens a new approach for producing featured nanostructures from organic templates.
| Maaloum, M., Muller, P., & Krafft, M. P. (2004). Lateral and vertical nanophase separation in Langmuir-Blodgett films of phospholipids and semifluorinated alkanes. Langmuir, 20(6), 2261–2264.|
Abstract: It has recently been found that monodisperse surface micelles (hemimicelles) were formed in Langmuir monolayers of the semifluorinated alkane C8F17C16H33 (F8H16) after transfer onto silicon wafers. Grazing incidence X-ray diffraction studies have demonstrated that compression of mixed Langmuir monolayers made from combinations of dipalmitoyl phosphatidylethanolamine (DPPE) and diblock F8H16 in various molar ratios resulted in the complete expulsion of the diblock molecule at high surface pressure. F8H16 then formed a second layer on top of a DPPE-only monolayer, demonstrating a novel type of reversible, pressure-induced, vertical phase separation. Using atomic force microscopy and X-ray reflectivity, we show now that mixed DPPE/F8H16 (1:1.3) Langmuir-Blodgett films transferred onto silicon wafers below 10 mN m(-1) are laterally phase separated and consist of domains of F8H16 surface micelles in coexistence with a monolayer of DPPE. The density of the network of F8H16 surface micelles increases when the surface pressure of transfer increases. Around 10 mN m(-1), the F8H16 surface micelles start to glide on the DPPE monolayer, progressively overlying it, until total coverage is achieved.
| Zhang, G. F., Maaloum, M., Muller, P., Benoit, N., & Krafft, M. P. (2004). Surface micelles of semifluorinated alkanes in Langmuir-Blodgett monolayers. Physical Chemistry Chemical Physics, 6(7), 1566–1569.|
Abstract: We have studied the molecular patterns formed in Langmuir-Blodgett (LB) films of semifluorinated alkanes CnF2n+1CmH2m+1 (FnHm diblocks, n = 6, 8, 10, m = 14, 16, 18, 20) by atomic force microscopy. All the compounds investigated formed surface micelles whose shape and dimensions varied with the molecular structure of the FnHm diblocks. Except for F6H16 and F8H14, which produced exclusively circular micelles, all of the other diblocks also formed elongated micelles that coexisted with circular micelles. The mean diameter of the circular micelles increased with the length of the hydrogenated segment of the diblocks. By contrast, increasing the length of the fluorinated segments did not have any detectable effect on the diameter. The elongated micelles became more numerous and longer for longer FnHm (both the length of the hydrogenated and of the fluorinated segments had a strong effect). The surface pressure of transfer had an influence on the morphology of the elongated micelles, the latter becoming fewer and shorter for higher surface pressures. A detailed X-ray reflectivity study conducted on F8H16 LB films showed that the hydrogenated segments are directed towards the silicon wafer, while the fluorinated segments point outwards toward the air. A disc-like model is proposed for the surface micelles.
| Krafft, M. P., Muller, P., Maaloum, M., Schmutz, M., Goldmann, M., & Fontaine, P. (2003). Micro phase separations induced by fluorinated chains in self-assembled molecular systems. Self-Assembly, , 367–373.|| |
| Maaloum, M., Muller, P., & Krafft, M. P. (2002). Monodisperse surface micelles of nonpolar amphiphiles in Langmuir monolayers. Angewandte Chemie-International Edition, 41(22), 4331–4334.|| |
| Barentin, C., Muller, P., Ybert, C., Joanny, J. F., & di Meglio, J. M. (2000). Shear viscosity of polymer and surfactant monolayers. European Physical Journal E, 2(2), 153–159.|
Abstract: The surface shear viscosity of monolayers formed at the surface of water by adsorbed polyethyl-eneoxyde and. by stearic acid is measured as a function of the surface pressure of the monolayer using a new surface viscometer. The principle of the viscometer is the measurement of the drag force on a circular disk undergoing a uniform translation at the water surface: a hydrodynamic model based on the lubrication approximation allows a calculation of the surface viscosities from the absolute measurement of the drag forces.
| Prinz, C., Muller, P., & Maaloum, M. (2000). Annealed polyelectrolyte brushes under normal and lateral compressions. Macromolecules, 33(13), 4896–4902.|
Abstract: We report here compression force measurements of diblock copolymers containing a short neutral hydrophobic sequence (polystyrene) and a long water-soluble weak polyelectrolyte sequence (poly(2-vinylpyridine)). This study focuses on the polyelectrolyte sequence and has been restricted to the case where the subphase is at pH 2. The lateral compressions were done using a Langmuir trough whereas the normal compressions were carried out with an atomic force microscope with a spherical particle attached to the tip. The thickness of the brush is considered as a function of the grafting density and is determined from the AFM force curves without reference to any theoretical model. At high grafting densities an “anomalous” behavior is observed, where the thickness of the brush decreases with increasing the grafting density. This is attributed to the annealed character of the polyelectrolyte.
| Prinz, C., Muller, P., & Maaloum, M. (2000). Langmuir isotherms of quenched and annealed polyelectrolyte brushes. Langmuir, 16(16), 6636–6640.|
Abstract: We report here Langmuir isotherms of diblock copolymers containing a short neutral hydrophobic sequence (polystyrene) and a long water-soluble polyelectrolyte sequence (polyvinyl-2-pyridine). This study focuses on the polyelectrolyte sequence, which is a weak polyelectrolyte when unmodified and strong polyelectrolyte when quaternized. In pure water, the surface pressure of the quenched brush is proportional to the osmotic pressure of the counterions. In water at pH 2, the annealed brush isotherms are those of a polyelectrolyte brush in the strong screening limit. In water at pH 3, a plateau appears in the annealed layer isotherms, revealing a transition from a state where the polyelectrolyte sequence is adsorbed at the interface to a strong polyelectrolyte brush state. It is not clear whether this transition is a first-order transition or a continuous compression-induced solubility of the PVP chains.
| Mesini, P., Schmidt, R., Decher, G., & Muller, P. (1999). Toward folding control in oligomeric systems. In Abstracts Of Papers Of The American Chemical Society (Vol. 217, 155-PMSE).|| |
| Barentin, C., Muller, P., & Joanny, J. F. (1998). Polymer brushes formed by end-capped poly(ethylene oxide) (PEO) at the air-water interface. Macromolecules, 31(7), 2198–2211.|
Abstract: We study monolayers formed at an air-water interface on a Langmuir trough by telechelic poly(ethylene oxide) polymers end capped with hydrophobic alkane groups (C-12 and C-16) The pressure-area isotherms show two plateaus: the first plateau at low coverage already exists for nontelechelic PEO and is attributed to the formation of loops in the solution; after this plateau, the pressure rises stongly as the hydrophobic groups anchor the polymers on the surface, which leads to the formation of a grafted polymer layer; the second plateau at high density is due to a dissolution of the polymer chains in the bulk water. Starting from a monolayer at high density, we also study experimentally the relaxation of the surface pressure with time due to the dissolution of the polymer. A theoretical approach of this problem based on polymer brush theory is proposed. Both the static properties of the layer and the desorption kinetics are calculated. The model accounts well for the shape of the isotherms and for the relaxation kinetics. It gives a good interpretation of the role of various parameters such as the compression velocity, the molecular weight, and the hydrophobicity of the chain ends. The anchoring energy of the hydrophobic groups is determined by comparison with experiments.
| Muller, P., Bliznyuk, V., & Mohwald, H. (1996). In-plane photoconduction in two-dimensional crystals in monolayers. Thin Solid Films, 272(1), 137–142.|
Abstract: We have built an experimental set-up allowing us to measure photoconduction in the plane of single monolayers. The monolayers are deposited by the Langmuir-Blodgett technique onto a quartz plate with two interdigitated electrodes. The electrode separation distance is 10 μm, smaller than the typical domain size in the studied monolayers. This enables one to perform photoconduction measurements through single two-dimensional crystals. Water-soluble charged cyanine dyes can be adsorbed onto an oppositely charged monolayer. These molecules form monocrystalline rectangular domains of typical size 100 X 20 μm(2). The photoconduction of these domains is studied here. The photoconduction spectrum follows the absorption spectrum of the system (but with a better efficiency for the aggregate bands) indicating that the charge carrier generation occurs through exciton dissociation. When using a polymerizable monolayer, the photoconduction process is greatly altered after polymerisation: the relaxation time of the photocurrent is two orders of magnitude faster and the spectrum shows an additional band at shorter wavelength where almost no absorption takes place.