An original setup combining a very stable loading stage, an atomic force microscopy and an environmental chamber, allows to obtain very stable sub-critical fracture propagation in oxide glasses under controlled environment, and subsequently to finely characterize the nanometric roughness properties of the crack surfaces. In this presentation, I will focus, on one hand, on the special experimental care that has to be devoted to measure the metrological properties of such nanometric rough surface by Atomic Force Microscopy (AFM) and, on the other hand, on the interest of analyses in terms of physical indicators related to the self-affine nature of the fracture surfaces. Due to the comparable nanometric amplitude of the surface roughness, the AFM tip size and the instrumental noise, it seems interesting to discuss about potential experimental artefacts highlighted by Lechenault et al. The roughness amplitude of several oxide glasses was shown to decrease as a function of the stress intensity factor, to be quite insensitive to the relative humidity and to increase with the content of network modifiers . These results will be discussed in terms on several modellings concerning the coupling between crack propagation, material heterogeneity, crack tip plastic deformation and water diffusion at the crack tip taking into account the self-affine nature of the fracture surfaces.

Polymer nanocomposites (PNCs) are made by dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Such materials attract industrial interest and their investigation is essential for the improvement of their performances. The present study concerns nanocomposites obtained using hydrophilic silica nanoparticles (NPs) dispersed in a soft polymer matrix of styrene-butadiene, commonly used in car tire manufacturing. The mechanical performances of such PNCs are strongly related to the structural properties: the dispersion state of silica particles in the polymer melt is governed by the mixing protocols (e.g., solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence the filler-filler and the filler-polymer interactions.We have developed a new model nanocomposite system, equivalent to a simplified industrial one [1,2], made by solvent casting technique using colloidal silica NPs. In such model PNCs, the dispersion of colloidal silica is tuned via the surface-modification of silica particles by grafting hydrophobic molecules, i.e., silane coating agents, which promote the filler-polymer compatibility.To describe NP structure in solvents and after casting in a polymer matrix, we propose a new method which combines Small Angle X-ray Scattering (SAXS), reverse Monte Carlo (RMC) and aggregate recognition (AR) analysis [3]. This approach allows obtaining a detailed structural characterization of the silica NPs surface-modified with different silane grafting groups (i.e., tri-ethoxy, tri-methoxy or mono-methoxy silane). In particular, this analysis suggests that silane molecules with trifunctional grafting functions lead to the formation of polycondensed patches (i.e., reaction of lateral groups with neighboring molecules) on silica surface, favoring attractive interactions. On the other hand, the lowest aggregation is observed using mono-functionalized silane molecules where patches cannot form. In the near future, the SAXS-RMC-AR approach will be extended to investigate the structural properties of nanocomposite systems where silica NPs are surface-modified with silane molecules of various alkyl chain [4].[1] D. Musino, A.C. Genix, C. Fayolle, A. Papon, L. Guy, N. Meissner, R. Kozak, P. Weda, T. Bizien, T. Chaussée, and J. Oberdisse,, Macromolecules (2017)[2] G. P. Baeza, A.-C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty, J. Oberdisse, Macromolecules (2013)[3] D. Musino, A.-C. Genix, T. Chaussée, L. Guy, N. Meissner, R. Kozak, T. Bizien, J. Oberdisse, Langmuir (2018)[4] D. Musino et al., in preparation

Gliadins are edible wheat storage proteins well known for their surface active properties. In this paper, we present experimental results on the interfacial properties of acidic solutions of gliadin studied over 5 decades of concentrations, from 0.001 to 110 g/L. Dynamic pendant drop tensiometry reveals that the surface pressure  of gliadin solutions builds up in a multistep process. The series of curves of the time evolution of collected at different bulk protein concentrations C can be merged onto a single master curve when  is plotted as a function of t where t is the time elapsed since the formation of the air/water interface and  is a shift parameter that varies with C as a power law with an exponent 2. The existence of such time-concentration superposition, which we evidence for the first time, indicates that the same mechanisms govern the surface tension evolution at all concentrations and are accelerated by an increase of the bulk concentration. The scaling of  with C is consistent with a kinetic of adsorption controlled by the diffusion of the proteins in the bulk. Moreover, we show that the proteins adsorption at the air/water interface is kinetically irreversible. Correlated evolutions of the optical and elastic properties of the interfaces, as probed by ellipsometry and surface dilatational rheology respectively, provide a consistent physical picture of the building up of the protein interfacial layer. A progressive coverage of the interface by the proteins occurs at low . This stage is followed, at higher , by conformational rearrangements of the protein film, which are identified by a strong increase of the dissipative viscoelastic properties of the film concomitantly with a peculiar evolution of its optical profile that we have rationalized. In the last stage, at even higher surface pressure, the adsorption is arrested; the optical profile is not modified while the elasticity of the interfacial layer dramatically increases with the surface pressure, presumably due to the film ageing.