Master 2ème année Année 2014-2015 PROPOSITION DE SUJET DE STAGE Nom du laboratoire : Laboratoire de Physique des Solides Adresse : Centre Scientifique d’Orsay, Bâtiment 510, 91405 Orsay CEDEX Nom du ou des responsables du stage : Alesya Mikhailovskaia et Anniina Salonen E-mail : email@example.com , firstname.lastname@example.org Téléphone : 01 69 15 59 86, 01 69 15 53 88 Page web : http://chercheurs.lps.u-psud.fr/Sil/spip.php?article47 Possibilité de poursuivre en thèse : oui non X Titre : How does a colloidal gel form inside a foam ? Résumé : Colloidal particles (particles with a radius from a few nms to µms) can aggregate and form space spanning networks of elastic gels under the right conditions. The structure of the aggregates and the gels depends intricately on the interaction potential between the particles. Fortuitously in the case of colloidal particles we have many levers to control these interactions, allowing us to play with the detailed phase behaviour of the particles and the strength of the resulting structures. This makes them particularly interesting for the design of light materials with interesting mechanical properties using foams. Bubbles dispersed in an aqueous phase constitute a foam and they are surrounded by a network of interconnected channels, composing the foam skeleton (see Figure below). The size of the channels can be controlled through the bubble size and the liquid fraction within the foam. The aim of the project is to study colloidal gel formation inside the foam skeleton. We want to understand both how the silica gel develops when constrained inside the soft walls of the foam network, the influence of confinement on colloidal gel formation. Secondly we want to use the stable foams generated to make solid foams through evaporation of the water phase, controlling the microstructure of the solid foams. The experimental project will use colloidal silica particles, which can be made to gel either through the addition of electrolytes or depleting polymers. The main interest of the project is the multiscale approach to the characterization of the gelification process. The local structure of the gels will be probed using small angle neutron scattering and the dynamics of the particles using light scattering (diffusing wave spectroscopy).  L. Arriaga, W. Drenckhan, A. Salonen, J. Rodrigues, R. Íñiguez-Palomares, E. Rio and D. Langevin, On the long-term stability of foams stabilised by mixtures of nano-particles and oppositely charged short chain surfactants. Soft Matter,8, 11085-11097 (2012).