Depletion Interaction Mediated by fd-Virus: on the Limit of Low Density and Derjaguin Approximation

Abstract

Abstract Depletion potentials induced by the rod-like fd-virus between colloidal probe spheres and a flat glass wall were measured using total internal reflection microscopy. The objective of this investigation was to determine the limits of the approximations used for the theoretical description of the depletion pair potential. Data were obtained at rod concentrations as high as 15 times their overlap concentration and the size ratio between the rod length and the sphere radius increased up to L/R = 1.76. With this, the basic assumptions for low density approximation and Derjaguin approximation were clearly violated. Nevertheless, we observed good agreement between experimental data and predictions up to the highest size ratio and in rod concentrations of seven times their overlap concentration. Only at higher concentrations and at the lowest size ratio investigated the experimental data deviate significantly from the simple model.