Soutenance de Jacques Blin

The presentation will be held in English and will cover part of my work conducted over the last three years at the laboratory, under the supervision of Thibaut Divoux and Sébastien Manneville, shortly summarized below. The defense jury will be composed of Laurence Ramos (Univ. of Montpellier, CNRS), Jasper van der Gucht (Wageningen University & Research), Guilhem Baeza (Jean Monnet Univ. in St Etienne), Pavlik Lettinga (KU Leuven & FZJ) and Véronique Trappe (Univ. of Fribourg). Additionally, a Zoom link will be shared on the day of the defense for those who wish to attend remotely.

Abstract

Colloid-polymer mixtures show remarkable mechanical properties linked to their self-assembly, finely tuned by the system’s physico-chemistry. This thesis focuses on three model systems whose interactions and microstructures are calibrated by a well-controlled physico-chemistry. By a thorough rheological investigation, we characterize the impact of shear history on the connectivity of these structures, through shear-induced rearrangements and phase transitions.

First, by studying the phase diagram of aqueous suspensions of fumed silica/poly(ethylene oxide), we show using small-angle X ray scattering (SAXS) that colloids’ auto-assembly is controlled by their surface coverage by adsorbed polymer. Two classes of microstructures are then identified, associated with two evolution modes of flow curves and viscoelastic properties.

Next, the study of fumed silica/polyacrylamide (PAM) gelation shows a time-connectivity superposition principle. By tuning colloid/polymer interactions through the glycerol/water ratio in the solvent, we demonstrate an universal behavior following a time-composition superposition principle, evidenced by SAXS analysis and X ray photon correlation spectroscopy (XPCS). Below the gel point, suspensions show a shear-induced liquid-gel transition, whose characteristics result from a strong coupling between aging and shear. Their study using rheo-SAXS show that structuration and anisotropy under flow are precursors to the phase transition.

At last, we study suspensions of breakable non-Brownian agglomerates of silica in PAM. Their flow properties exhibit two distinct evolution regimes separated by a critical shear-rate. Below, viscoelasticity varies reversibly according a strain-connectivity superposition principle. Above, shear leads to an irreversible agglomerate degradation, described by degradation-connectivity superposition principle.

As such, these studies bring a new perspective on the use of shear as an experimental control parameter allowing to tune structure and connectivity of colloid-polymer suspensions.