FLUID-FLUID PHASE-SEPARATION IN COLLOID-POLYMER MIXTURES STUDIED WITHSMALL-ANGLE LIGHT-SCATTERING AND LIGHT-MICROSCOPY

Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclo hexane with a colloid-polymer size ratio of about one were found to ph ase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of t his fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersatur ation, with small angle light scattering and with light microscopy. Th e small angle light scattering curve exhibits a peak that grows in int ensity and that shifts to smaller wave vector with time. The character istic length scale that is obtained from the scattering peak is of the order of a few mu m, in agreement with observations by light microsco py. The domain size increases with time as t(1/3), which might be an i ndication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low de grees of supersaturation the angular scattering intensity curves satis fy dynamical scaling behavior.