Small-angle scattering applied to the sequence of morphologies of self-assembled structures

Small-angle scattering applied to microemulsions and liquid crystals

Experimental and theoretical approaches to the many faces of interfaces.

Conformation of polymer chains, chain statistics,polymer solutions and blends, thermodynamics,phase separation, mechanical properties.

Polymer nanocomposites are mixtures of nanoparticles (NPs) and polymer chains, where the filler particles are usually added to enhance mechanical properties, e.g. of car tire materials. Performance depends to a great extent on the structure of the filler, i.e. its dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned via the surface-modification of the nanoparticles by grafting small hydrophobic molecules (coating agents), which promote the filler-polymer compatibility. In this talk, different ways to obtain information from small-angle scattering on the structure of nanocomposites will be presented using either the recently proposed correlation hole analysis [1] or reverse Monte-Carlo (RMC) analysis giving access to aggregate mass distributions [2]. In particular, we will review recent results on model nanocomposites – and their industrial counterparts – using surface-modified silica NPs with different types of silane groups (tri-ethoxy or mono-methoxy) and silanes of different lengths. To describe NP structure in solvents and after casting in a polymer matrix, we propose a new method which combines SAXS, RMC and aggregate recognition analysis [2]. 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. Finally, regarding chain structure, a quick outlook on why contrast-matching with SANS in nanocomposites often fails will be proposed [3]. [1] A.-C. Genix and J. Oberdisse, Soft Matter 2017, 13, 8144. [2] D. Musino, A.-C. Genix, T. Chaussée, L. Guy, N. Meissner, R. Kozak, T. Bizien, J. Oberdisse, Langmuir 2018, 34, 3010. [3] A. Banc, A.-C. Genix, C. Dupas, M. Sztucki, R. Schweins, M.-S. Appavou, J. Oberdisse, Macromolecules 2015, 48, 6596.

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.