Investigating dynamics of colloids confined in a foam with Dynamic Light Scattering
Résumé
We present a experimental method which allow to investigate the dynamics of brownian colloidal particles dispersed in the liquid phase of a foam[1]. We illuminate the mixture foam+colloids with a coherent source, and the scattered light is measured. The temporal auto-correlation function of the scattered intensity of the light shows two decays occurring at two different timescales. At short times, the brownian motion of particles is measured, and at long time, the aging of the foam is recorded. This two characteristic times decay of the correlation function may be described using a Diffusive Wave Spectroscopy model coupling two kinds of scattering events: firstly scattering of light by the foam skeleton, and secondly scattering by colloidal particles. A statistical optical model of this random walk allows to reproduce the time variation of the temporal autocorrelation function of the scattered light. The concentration and the mobility of the colloidal particles may be deduced from the experiments. The predictions of the model are in agreement with experiments where we varied the quantity and the size of the colloidal particles[1]. Extension to colloidal particles dispersed into a Pickering foam[2] and into a porous material made of dielectric spheres will be mentioned[3].