The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. While the structure of the hard filler phase is usually characterized by electron microscopy and small-angle X-ray scattering, the chain conformation can only be measured by small-angle neutron scattering (SANS).

Structuring wheat gluten proteins into gels with tunable mechanical properties would provide more versatility for the production of plant protein-rich food products. Gluten, a strongly elastic protein material insoluble in water, is hardly processable. We use a novel fractionation procedure allowing the isolation from gluten of a water/ethanol soluble protein blend, enriched in glutenin polymers at an unprecedented high ratio (50%). We investigate here the viscoelasticity of suspensions of the protein blend in a water/ethanol (50/50 v/v) solvent, and show that, over a wide range of concentrations, they undergo a spontaneous gelation driven by hydrogen bonding. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The gluten gels display self-healing properties and their elastic plateaus cover several decades, from 0.01 to 10,000 Pa. In particular very soft gels as compared to standard hydrated gluten can be produced.

SANS study of a gluten protein gel: Why are SAXS and SANS profiles diffrents?

Les nanocomposites de polymère sont des matériaux dont la matrice polymère est renforcée par des nanoparticules (NPs), comme par exemple des NPs de silice. Pouvoir contrôler la structuration de ces dernières au sein de la matrice est un vieux rêve, parce que l’on espère pouvoir ajuster les propriétés macroscopiques via la microstructure. Dans un premier temps, nous montrerons quelques exemples d’analyse structurale de nanocomposites par diffusion de rayonnement aux petits angles, simulation numérique, et microscopie électronique [1]. Ces études mettent en évidence le caractère en partie hors équilibre de ces structures. Ces dernières années, un paramètre de contrôle des structuration des NPs à l’équilibre est apparu [2-4] : le greffage de chaînes de polymère à la surface des NPs. Il permet de contrôler l’agrégation des NPs, et d’obtenir des structures anisotropes essentiellement visualisées par TEM. Même si cela n’a pas encore trouvé d’écho dans la littérature de mode, la coiffure semble donc être liée au rangement, au moins pour les toutes petites billes. Pour finir, nous discuterons d’un modèle structural développé pour des systèmes plus proches des applications industrielles, et nettement moins enclins à une structuration ordonnée, malgré les efforts de greffage [5]. Références: 1 A. Banc, A.-C. Genix, M. Chirat, C. Dupas, S. Caillol, M. Sztucki, J. Oberdisse, Macromolecules 2014, 47 (9), 3219–32302 A. El Harrak, G. Carrot, J. Oberdisse, Ch. Eychenne-Baron, F. Boué, Macromolecules 2004, 37, 6376-63843 P. Akcora et al, Nature Mat 2009, 8, 354-3594 S. Kumar, N. Jouault, B. Benicewicz, T. Neely Macromolecules 2013, 46, 3199-32145 G. P. Baeza, A.-C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty, J. Oberdisse, Macromolecules 2013, 46, 317−329

TBA.

The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. While the structure of the hard filler nanoparticles (NPs) is usually characterized by electron microscopy and small-angle X-ray scattering (SAXS), the chain conformation can only be measured by small-angle neutron scattering (SANS). Two main difficulties may arise with such a structural analysis. First of all, extracting reliable structural information on filler dispersion may be hindered by lack of a priori knowledge of the system. In this talk, we will discuss two examples. In the first one, additional knowledge is due to the model character of well-characterized NPs, and it can be used to analyze scattering data using Monte Carlo simulations [1]. In the second one, industrial filler NPs of high structural complexity have been used, and structural characterization of this system was only possible by quantitatively combining MC simulations, transmission electron microscopy, and SAXS [2]. Concerning the determination of polymer conformation by SANS, a second and mostly unforeseen difficulty shows up: in spite of great care in contrast-matching (undesired) NP contributions to the SANS signal, such additional intensities are systematically found in the literature. Two model cases are discussed in this talk: the first one emphasizes large-scale polymer heterogeneities reminiscent of the solution structure before nanocomposite formation. This structure is described quantitatively by a ‘hairy bead’ model [3]. The second one, finally, is the result of a general study of incomplete filler NP matching, evidencing for the first time that smallest NPs may induce statistical fluctuations in H-D-density in a surrounding shell, making in principle matched filler visible. Incidentally, the typical size of such mismatched polymer shells is deduced from the data [4]. [1] A. Banc et al, Macromolecules 47 (9), 3219–3230 (2014); J. Oberdisse et al Soft Matter, 3, 476-485 (2007)[2] G. Baeza et al, Soft Matter 10, 6686-6695 (2014)[3] A.C. Genix et al, Macromolecules 45(3), 1663-1675 (2012)[4] A. Banc et al, submitted