Charged Micelle Depletion Attraction and Interfacial Colloidal Phase Behavior

Ensemble total internal reflection microscopy (TIRM) is used to directly measure the evolution of colloid−surface depletion attraction with increasing sodium dodecyl sulfate (SDS) concentration near the critical micelle concentration (CMC). Measured potentials are well described by a modified Asakura−Oosawa (AO) depletion potential in addition to electrostatic and van der Waals contributions. The modified AO potential includes effects of electrostatic interactions between micelles and surfaces via effective depletant dimensions in an excluded volume term and partitioning in an osmotic pressure term. Directly measured colloid−surface depletion potentials are used in Monte Carlo (MC) simulations to capture video microscopy (VM) measurements of micelle-mediated quasi-two-dimensional phase behavior including fluid, crystal, and gel microstructures. Our findings provide information to develop more rigorous and analytically simple models of depletion attraction in charged micellar systems.