| In this thesis, the phase behavior and osmotic compressibility of model athermal silica - polystyrene suspensions has been determined over nearly two orders of magnitude in polymer/colloid size asymmetry. Fluid-gel, fluid-crystal, and fluid-fluid transitions are observed as Rg, the polymer radius of gyration, increases. Based on the polymer concentration relative to the dilute-semidilute crossover density, cp/cp*, as the relevant measure of depletion attraction, we find that suspension miscibility monotonically improves as Rg increases for all colloid volume fractions. This trend is in contradiction with all classic depletion theories we are aware of. However, the predictions of fluid-fluid spinodal phase separation by the microscopic Polymer Reference Interaction Site Model (PRISM) integral equation theory of athermal polymercolloid suspensions is in agreement with the experimental observations. PRISM is also very successful in predicting the compressibility curves if cp/cp* is taken as an adjustable parameter. Polymer-polymer interactions, chain fractal structure, and structural reorganizations are implicated as critical physical factors. |
