The ability of colloidal particles to self-organize suggests that colloidal particles could be used as precursors for advanced materials via the generation of complex microstructures. The precise control of colloidal dispersions rests upon our knowledge of the forces that arise between particles and surfaces of various shapes. An important class of inter-particle forces is induced by the presence of other colloidal species and arises solely as a result of entropic considerations. These entropic forces can promote order-disorder transitions in the dispersion microstructure and may be responsible for a disorder-disorder transition. Furthermore, passive structures etched into the walls of the container can create entropic force fields of sufficient range and magnitude so that the motion and position of large colloids can be controlled, thereby generating various two-dimensional fluid-like and solid-like phases on chosen templates.

By providing new and potentially simple routes for the directed self-assembly of novel mesoscopic structures, the use of entropic force fields to create various complex microstructures is a promising approach to the production of advanced materials. Various issues concerning the feasibility of such methods, however, need to be addressed. For example, the dynamics of colloidal particles diffusing through an entropic force field is not well known. Since the entropic forces that arise within colloidal dispersions become repulsive at intermediate separations, large repulsive barriers may kinetically stabilize suspensions even though coagulation/deposition is thermodynamically favored. In some instances, these repulsive barriers may prevent the desired deposition or coagulation.

We investigate in detail the dynamics of hard-sphere colloids moving above and onto surfaces of various shapes via the use of two computational methods: molecular dynamics (MD) and stochastic rotation dynamics (SRD). SRD, which is a method for coarse-graining fluid interactions while still including the correct hydrodynamic interactions, such as the important lubrication forces, allows us to determine the relative influence of hydrodynamic and entropic effects on particle deposition. We find good agreement between our calculated and previously measured (via experiments) normal and transverse diffusion coefficients of a colloid particle located near a hard wall. A comparison of MD and SRD results also reveals that SRD captures interesting solvent behavior when the gap distance between colloids or between colloids and surfaces become quite small. While no simulation method is optimal for all systems of interest, our studies indicate that SRD is a robust computational tool that should be applicable to a reasonable variety of other technologically relevant colloidal dispersions.