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International audience; The saponin aescin, a mixture of triterpenoid saponins, is obtained from the seeds of the horse chestnut tree Aesculus hippocastanum. The beta-form employed in this study is haemolytically active. The haemolytic activity results from the ability of aescin to form strong complexes with cholesterol in the red blood cell membrane. In this study, we provide a structural analysis on the complex formation of aescin and cholesterol when embedded in a phospholipid model membrane formed by 1,2-dimyristoylsn-glycero-3-phosphocholine (DMPC). In this work, the temperatures investigated extend from DMPC's L-beta' to its L-alpha phase in dependence of different amounts of the saponin (0-6 mol% for calorimetric and 0-1 mol% for structural analyses) and the steroid (1-10 mol%). At these aescin contents model membranes are conserved in the form of small unilamellar vesicles (SUVs) and major overall structural modifications are avoided. Additionally, interactions between aescin and cholesterol can be studied for both phase states of the lipid, the gel and the fluid state. From calorimetric experiments by differential scanning calorimetry (DSC), it could be shown that both, the steroid and the saponin content, have a significant impact on the cooperative phase transition behaviour of the DMPC molecules. In addition, it becomes clearly visible that the entire phase behaviour is dominated by phase separation which indeed also depends on the complexes formed between aescin and cholesterol. We show by various methods that the addition of cholesterol alters the impact of aescin on structural parameters ranging from the acyl chain correlation to vesicle-vesicle interactions. While the specific saponin-phospholipid interaction is reduced, addition of cholesterol leads to deformation of SUVs. The analyses of the structures formed were performed by wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS).

International audience; We designed stable and highly reproducible hydrogels by external unidirectional diffusion of Fe2+ ions into aqueous solutions of polygalacturonate (polyGal) chains. The Fe2+ ions act as cross-linkers between the Gal units in such a way that both the molar ratio R ([Fe2+]/[Galunits]=0.25) and the mesh size of the polyGal network at the local scale (zeta=75 +/- 5 angstrom) have constant values within the whole gel, as respectively determined by titration and Small Angle Neutron Scattering. From macroscopic point of view, there is a progressive decrease of polyGal concentration from the part of the gel formed in the early stages of the gelation process, which is homogeneous, transparent and whose Young modulus has a high value of similar to 10(5) Pa, up to the part of the gel formed in the late stages, which is heterogeneous, highly turbid and has a much lower Young modulus of similar to 10(3) Pa. Since the local organization of the polyGal chains remains identical all along the hydrogels, this macroscopic concentration gradient originates from the formation of heterogeneities at a mesoscopic length scale during the gelation process. In addition, X-ray Absorption Spectroscopy measurements remarkably reveal that Fe2+ ions keep their +II oxidation state in the whole gels once they have cross-linked the Gal units. These polyGal hydrogels thus protect iron against oxidation and could be used for iron fortification.

International audience; Solid lipid nanoparticles (SLN) stabilized by nonionic polysorbate or block copolymer surfactants were used for the preparation of hierarchical meso-macroporous silica through a co-templated approach combining a cooperative templating mechanism (CTM) with micelles and spherical soft matter particles imprinting. Depending on the reaction conditions, the morphology of the final material can be tuned to capsules or to block matter. The size of the mesopores is strongly dependent on the nature of the surfactant in excess: 3 nm (Tween 20), 5 nm (Tween 40) or 9 nm (Pluronic (R) P123), whereas the size of the macropores depends only on the size of SLN (250 +/- 150 nm). The macroporous texture was clearly evidenced by TEM. The organization degree of the silica wall depends on the surfactant: only wormlike mesoporous capsules were obtained with Tween 20, and hexagonally ordered microdomains embedded in wormlike mesoporous silica capsules were obtained with Tween 40. Hexagonally ordered silica with circularly ordered mesoporosity could be achieved with Pluronic block copolymer P123. Combining mesoporous silica with solid lipid nanoparticles is a straightforward approach for the design of advanced formulations in drug delivery or food chemistry.

The modification of silica nanoparticles with hexafluoropropylene oxide (HFPO) oligomers has been investigated. HFPO oligomers with two different average degrees of polymerization (DPn = 8 and 15) were first prepared by anionic ring-opening polymerization, deactivated by methanol, and in some cases postfunctionalized by aminopropyl(tri)ethoxysilane or allylamine. The "grafting onto" reactions of these oligomers were then carried out either on bare silica (reaction between a silanol surface and ethoxy-silanized HFPO) or on silica functionalized by amino groups (in an amidation reaction with methyl ester-ended HFPO) or mercapto groups (via the radical addition of allyl-functionalized HFPO). Hybrid nanoparticles thus obtained were characterized by solid-state Si-29 NMR and FTIR spectroscopies as well as elemental and thermogravimetric analyses. The results assessed a significant yield of covalent grafting of HFPO oligomers when performing the hydrolysis-condensation of ethoxylated HFPO on the bare silica surface, compared to the other two methods that merely led to physically adsorbed HFPO chains. Chemically grafted nanohybrids showed a high thermal stability (up to 400 degrees C) as well as a very low surface tension (typically 5 mN/m) compared to physisorbed complexes.

International audience; We recently described the synthesis and phase behavior of a new type of CECEC-P multiblock copolymer composed of glassy poly(cyclohexylethylene) (C), semicrystalline poly(ethylene) (E), and elastomeric poly(ethylene-alt-propylene) (P) with symmetric (equal volume) CECEC and P sequences (G. Fleury and F. S. Bates, Macromolecules, 2009, 42, 3598-3610). Here we report the formation and characterization of a multicontinuous structure based on the blending of CEC triblock copolymer and P homopolymer with such a hexablock copolymer along the 50 : 50 (CEC/P) isopleth. These materials produce a sequence of phases that are correlated with the volume fraction of CECEC-P as evidenced by SAXS and TEM measurements. A percolating bicontinuous mesostructure was identified at volume fractions of hexablock copolymer, f(CECEC-P)=0.10 and 0.125, within the composition range known to result in a bicontinuous morphology in A-B/A/B systems. A solid product was formed by cooling the initially homogeneous ternary mixture from above the melting temperature of the E blocks to room temperature. Crystallization of E leads to microphase separation of C and E and simultaneous ejection of P from CEC (and CECEC) at a larger length scale. The mechanical properties of these materials are inferior to what is anticipated based on pure CEC triblock copolymer, attributable to the low molecular weight and irregular structure of the C/E region sequences. Nevertheless, this study establishes a procedure for producing bicontinuous yet structurally asymmetric materials based on the microemulsion process and extends the concept of a microemulsion to multiblock copolymers.

International audience; We report on a new class of self-assembled transient networks made of surfactant micelles of tunable morphology (from spheres, to rodlike to wormlike) reversibly linked by telechelic polymers. Linear rheological measurements show that three distinct domains can be defined depending on the morphologies of the micelles: a domain where the micelles are isolated and not entangled, an intermediate domain where the micelles are partially entangled and a domain where the micelles are fully entangled. Flow curves of the transient networks of tunable morphology suggest that one can associate to the three domains distinct failures modes: a brittle mode, an intermediate mode and finally a ductile/shear banding mode, as the micelles grow. Thanks to this unique class of self-assembled networks, a continuous failure mode transition from brittle to ductile has been evidenced.

A method allowing the evaluation of the solvophilic/solvophobic character of polyelectrolytes from their conformation in solution is discussed. Analyzed systems are salt-free aqueous solutions of natural copolysaccharides with controlled chemical structures. Small-angle X-ray scattering diagrams revealed their conformation by the "polyelectrolyte peak". The study of this peak allowed the determination of c(b), the crossover concentration associated with the transition between the two structural organization regimes predicted by the scaling model of hydrophobic polyelectrolytes developed by Dobrynin and Rubinstein.(1) A structural law of behavior as a function of the chain primary structure is built for chitosan, showing an increasing hydrophobic character when the fraction of N-acetyl-D-glucosamine residues (DA) increases. The results concerning this random copolymer are compared with those obtained for hyaluronan. Consistently, in the case of alginates, the relative content of the constitutive units is shown not to influence the polymer hydrophobicity.

International audience; We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.

If one expands the expression of the intensity scattered by polymers or copolymers in the large q range, one observes that, for Gaussian chains, this intensity follows a law of the type i(q) = Aq-2 + Bq-4. The coefficient A characterizes the length of the statistical element, and the coefficient B is easily measured using the Zimm representation. For a linear chain B gives the number-average degree of polymerization. In the case of branched polymers without loops, it depends mainly on the number of statistical elements between two cross-links or one cross-link and an end. If the polymer is sufficiently long, it gives the number-average degree of polymerization of these branches. A general formula is given and applied to classical examples: star, alternating, a comblike copolymer. The effect of polydispersity and the case of block copolymers with blocks of different chemical nature are discussed. These results are also extended to stretched polymers. This method could give new information in the interpretation of neutron scattering data.