Influence of nanoscale surface topographical heterogeneity on colloidal interactions

Abstract

In this thesis, measurement and analysis of colloidal forces between an atomic force microscope (AFM) probe and a topographically patterned substrate are reported. The energy between the patterned substrate and a smooth flat plate was characterized mathematically using Surface Element Integration (SEI) method. Hemispherical, conical, and cylindrical shape asperities in form of either protrusions or depressions were arrayed on a square lattice to model the rough surface. The variation of DLVO interaction energies on such nano-patterned surfaces was investigated as a function of the size and density of the asperities. It was demonstrated that roughness elements attenuate the near-field DLVO energy by orders of magnitude, whereas at larger separations, their effect is insignificant. The interaction of an AFM hemispherical model probe and a rough surface was also calculated when the probe laterally moves over the surface. The resulting energy distribution maps reveal how the AFM experimental force-distance measurements can vary depending on the lateral position of the probe on the patterned substrate.