We measured gas and water permeability in sets of nano-composite silica gels, (silica gel network withaerosil particles), which are highly porous but low permeability materials. Experimental results showedthat gas and liquid permeability increased with aerosil content, allowing control of transport properties.Our results also showed that gas permeability was more than one order of magnitude higher than waterpermeability. This difference was analysed in view of the gas slippage effect. To this end, we tested andcompared different correction factor models (Knudsen and Klinkenberg correction factors) proposed inthe literature. We showed that the Klinkenberg factor increases with porosity, and discuss the effect oftortuosity. Models that account for porosity and tortuosity improve the accuracy of the prediction. TheKnudsen correction increased the accuracy of the experimental data and made it possible to extrapolatethe intrinsic permeability from the gas permeability with quite reasonable accuracy.

Dispersion de silice modifiée dans l'eau

Dispersion de silice modifiée dans l'eau

Nanocomposites made of hard inorganic nanoparticles (NPs) embedded in a soft polymer matrix may have rheological properties of interest for various applications, and in particular car tires. These properties depend crucially on the dispersion of the filler NPs, which has been studied in simplified industrial (i.e., without crosslinker and related chemistry) styrene–butadiene nanocomposites with silica filler NPs. We have developed a quantitative structural analysis based on a combination of electron microscopy, Monte Carlo simulations, and small-angle X-ray scattering. It allowed us to establish a global structural model, where primary silica beads are organized within small aggregates, which themselves fill large-scale fractal branches. Experimental parameters have been varied independently, starting with the silica volume fraction si, the matrix composition (percentage of graftable chains), and the chain mass. The grafting density on the silica NPs was shown to be the structure- and rheology-determining parameter, and we will show that a simple mechanism is able to explain the evolution of aggregate size and mass with grafting density. Moreover, dynamical properties have been followed by broadband dielectric spectroscopy (BDS) recently, and the detailed characterization of two high-temperature silica-related processes provided evidence that one of them can be linked to the structural evolution of these nanocomposites. Our work thus suggests that such high-temperature BDS-measurements can be used to detect reorganizations in structurally complex silica nanocomposites.Baeza et al, Macromolecules 2013, ibid 2013, ACS Macro Letters 2014, Soft Matter 2014

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

Small-angle scattering applied to microemulsions and liquid crystals

I'll review the progress achieved in constructing the non-perturbative hypermultiplet moduli space using twistorial methods. The metric on this space determines the low-energy effective action of Type II string theory compactified on a Calabi-Yau threefold. It receives instanton corrections due to D-branes and NS5-branes and I'll show how all of them can be nicely incorporated at the level of the twistor space. I'll argue that the inclusion of NS5-brane instantons might be closely related to quantization of a certain integrable structure. If the time permits, I'll present also a conjecture for the Witten index of 4d N=2 gauge theories inspired by the twistorial description of the hypermultiplet moduli space.