Interactions between a solid spherical particle and a chemically heterogeneous planar substrate.

Abstract

The Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction forces between a chemically heterogeneous substrate and a spherical particle approaching the surface are calculated using a simple model. This model decomposes the heterogeneous substrate into nanoscale subunits and applies a pairwise summation of forces between each subunit and the approaching particle to determine the net DLVO force. This approach leads to a three-dimensional description of the forces arising from the chemical heterogeneity of the surface. In this three-dimensional realm, we observe the emergence of a substantial lateral force at specific separation distances from the substrate. More specifically, the lateral forces become significantly larger than the normal forces at separation distances between those of the repulsive barrier and the secondary minimum of the DLVO interaction energy curve. These lateral forces are most pronounced at high electrolyte concentrations, particularly at biological salt concentrations of approximately 0.1 M. Furthermore, the lateral forces are found to be significantly higher when the particle is near the edge of a heterogeneous region of the substrate. On the basis of the evidence of this study, and depending on the characteristics of the system, both the physical roughness and the chemical heterogeneity of a surface can significantly affect how a particle will interact with it.