Supported bilayers: combined specular and diffuse x-ray scattering

A new method is proposed for the analysis of specular and off-specular reflectivity from supported lipid bilayers. Both thermal fluctuations and the "static" roughness induced by the substrate are carefully taken into account. Examples from supported bilayers and more complex systems comprising a bilayer adsorbed or grafted on the substrate and another "floating" bilayer are given. The combined analysis of specular and off-specular reflectivity allows the precise determination of the structure of adsorbed and floating bilayers, their tension, bending rigidity and interaction potentials. We show that this new method gives a unique opportunity to investigate phenomena like protusion modes of adsorbed bilayers and opens the way to the investigation of more complex systems including different kinds of lipids, cholesterol or peptides

Easy orientation of diblock copolymers on self-assembled monolayers using UV irradiation

A simple method based on UV/ozone treatment is proposed to control the surface energy of dense grafted silane layers for orientating block copolymer mesophases. Our method allows one to tune the surface energy down to a fraction of a mN/m. We show that related to the surface, perpendicular orientation of a lamellar phase of a PS-PMMA diblock copolymer (neutral surface) is obtained for a critical surface energy of 23.9-25.7 mN/m. Perpendicular cylinders are obtained for 24.6 mN/m and parallel cylinders for 26.8 mN/m.Comment: 3 figures, 1 tabl

Controlling interactions in supported bilayers from weak electrostatic repulsion to high osmotic pressure

Understanding interactions between membranes requires measurements on well-controlled systems close to natural conditions, in which fluctuations play an important role. We have determined, by grazing incidence X-ray scattering, the interaction potential between two lipid bilayers, one adsorbed on a solid surface and the other floating close by. We find that interactions in this highly hydrated model system are two orders of magnitude softer than in previously reported work on multilayer stacks. This is attributed to the weak electrostatic repulsion due to the small fraction of ionized lipids in supported bilayers with a lower number of defects. Our data are consistent with the Poisson-Boltzmann theory, in the regime where repulsion is dominated by the entropy of counter ions. We also have unique access to very weak entropic repulsion potentials, which allowed us to discriminate between the various models proposed in the literature. We further demonstrate that the interaction potential between supported bilayers can be tuned at will by applying osmotic pressure, providing a way to manipulate these model membranes, thus considerably enlarging the range of biological or physical problems that can be addressed.Comment: 14 pages, 8 figure

Sliding tethered ligands add topological interactions to the toolbox of ligand-receptor design

International audienceAdhesion 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

Organization of Block Copolymers using NanoImprint Lithography: Comparison of Theory and Experiments

We present NanoImprint lithography experiments and modeling of thin films of block copolymers (BCP). The NanoImprint lithography is used to align perpendicularly lamellar phases, over distances much larger than the natural lamellar periodicity. The modeling relies on self-consistent field calculations done in two- and three-dimensions. We get a good agreement with the NanoImprint lithography setups. We find that, at thermodynamical equilibrium, the ordered BCP lamellae are much better aligned than when the films are deposited on uniform planar surfaces

Deux cas de films minces : l'etalement des polymeres sur differentes surfaces et les monocouches d'amphiphiles sur l'eau : une etude par rayons X aux incidences rasantes

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Les synchrotrons, de très grands instruments de la physique au service de toutes les autres disciplines

Que ce soit en France, en Europe, aux États-Unis, au Japon ou ailleurs dans le monde, trois mots-clés reviennent toujours lorsqu’on présente les synchrotrons et leurs activités : pluridisciplinarité, brillance, utilisateurs. Ces très grands instruments de la physique, considérés comme les sources de lumière les plus sophistiquées et les plus performantes, sont, en effet, au service de dizaines de milliers de chercheurs dans le monde, irriguant toutes les disciplines scientifiques. C’est ce qui constitue leur atout principal en tant qu’infrastructures de recherche : favoriser les synergies entre disciplines et les collaborations entre équipes en proposant, au même endroit et au même moment, un panel de techniques expérimentales et de compétences

Nanoparticules et microfluidique pour un système modèle d'émulsions de Pickering (étude des mécanismes de stabilisation et de déstabilisation)

Les émulsions stabilisées par des particules solides sont connues et étudiées depuis le début du XXème siècle, dans le but de comprendre les propriétés originales qu elles présentent. Afin de rationaliser ces systèmes, nous développons un système modèle basé sur l utilisation de techniques microfluidiques pour la fabrication de gouttes et de nanoparticules de silice monodisperses pour les stabiliser. La première partie de ce travail porte sur l optimisation et la compréhension de la synthèse diphasique des nanoparticules dans le cadre de la Théorie Classique de la Nucléation. Ces nanoparticules sont ensuite utilisées pour stabiliser des gouttes d huiles formées dans une puce microfluidique, ce qui permet de découpler les différents phénomènes conduisant à l obtention d une émulsion : création de surface, adsorption des particules, coalescence des gouttes. Les émulsions collectées peuvent être déstabilisées par ajout d un solvant dans la phase continue, provoquant la formation de gouttes non sphériques ou la séparation totale des deux phases. Enfin, nous examinons les mécanismes permettant d expliquer la stabilisation ou la déstabilisation provoquée des gouttes par des nanoparticulesEmulsions stabilized by solid particles are known and studied since the beginning of the XXth century, to understand the original properties they display. In order to rationalize these systems, we develop a model system based on the use of microfluidic techniques to create droplets and monodisperse silica nanoparticles to stabilize them. The first part of this work deals with the optimization and understanding of the two-phase particle synthesis, in light of Classical Nucleation Theory. These nanoparticles are then used to stabilize oil droplets formed inside a microfluidic chip, which enables the decoupling of various phenomena allowing the formation of an emulsion: surface creation, adsorption of particles, coalescence of drops. Resulting emulsions can be destabilized by addition of a solvent in the continuous phase, resulting either in the formation of non-spherical droplets or in the total separation of the two phases. Finally, we investigate the mechanisms explaining the stabilization and triggered destabilization of drops by nanoparticlesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF