Suppressing and enhancing depletion attractions between surfaces roughened by asperities.

By decorating the surfaces of smooth, flat platelets with hemispheroidal asperities and calculating the overlapping excluded volume of spherical depletion agents as two platelets approach face to face, we determine the depletion interaction potential for both ordered and disordered surface asperities. Depending on the surface morphologies, the depletion attraction between rough surfaces can be either dramatically reduced or amplified. A phase diagram of roughened Janus platelets is calculated and agrees well with prior experiments. This model explains the observed self-assembly of rough platelets and provides quantitative predictions of roughness-controlled depletion attractions for conditions that have not yet been explored experimentally.