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Soutenance de thèse : Louis Keal

Dynamics of hard and soft colloids at aqueous interfaces .
 

Thursday the 17th of November, at 14h30 in Amphi Joliot (ESPCI)
 
This thesis examines interfacial colloidal dynamics in two separate aqueous systems. The first part aims to improve understanding of thermoresponsive microgel-stabilised emulsions. Many emulsion properties are determined by the behaviour and drainage dynamics of the thin films that form between droplets. This study reveals these drainage dynamics, achieved through observing a model thin film of PNiPAM microgel solution in air.
 
We explore why, as other studies have shown, less cross-linked microgels stabilise emulsions more effectively than more cross-linked microgels, concluding that both adsorption dynamics and particle rearrangement under pressure play a role. Through a simple calculation, we are able to estimate the conformation of microgels at the interface, showing that microgel concentration in bulk determines the concentration at interface due to differences in adsorption kinetics, and microgel excess does not play a role.
 
The second part of the thesis investigates the behaviour of spherical colloidal particles with an Aqueous Two-Phase System (ATPS) composed of non-mixing polymer solutions of fish gelatin and dextran, with applications in low-fat foods. Additionally, the very low surface tension of these systems allows the study of fast interfacial processes at experimentally accessible timescales. In this work, we examine adsorption dynamics of spherical particles, observing for the first time the theoretically-predicted exponential ‘snap-in’ stage of particle adsorption. Surprisingly, even at this low surface tension, a slower logarithmic relaxation is subsequently observed which at the oil/water interface is ascribed to pinning of the contact line on surface defects.