(687b) Modified AO Potentials for Micellar, Nanoparticle, and Macromolecular Mediated Depletion Attraction & Colloidal Phase Behavior

Understanding depletion attraction between colloidal particles provides a basis to manipulate concentrated colloidal microstructures and phenomena ranging from suspension rheology to colloidal crystal assembly.  However, a universal approach does not exist for modeling depletion attraction in a wide range of material systems.  In this talk, we report a simple model that captures direct measurements of depletion potentials and phase behavior for micron sized colloids in the presence of charged micelles, charged nanoparticles, and nonionic macromolecules.  For sodium dodecyl sulfate micelles, Ludox nanoparticles, and polyethylene oxide random coils in aqueous media, we use total internal reflection microscopy to directly measure depletion potentials between micron sized colloids and surfaces.  In addition, video microscopy is used to directly measure quasi-2D interfacial phase behavior in the same material systems.  By using a modified Asakura-Oosawa (AO) potential, we are able to accurately model the directly measured particle-wall potentials and capture the interfacial phase behavior in Monte Carlo simulations, using a similar particle-particle potential.  The modified AO potential includes an effective depletant size in an excluded volume term and depletant partitioning in an osmotic pressure term.  Excellent agreement with experimental results and more rigorous theories for each material system suggests that the modified AO potential provides a model of depletion attraction that is more general and analytically simple than previous approaches.