Depletion forces near a soft surface

TL;DR

This paper explores how surface fluctuations influence depletion forces in colloidal suspensions near soft interfaces, revealing non-monotonic density profiles and potential for particle encapsulation.

Contribution

It introduces a model for depletion effects near flexible surfaces, showing how surface fluctuations alter particle distribution and interaction potentials.

Findings

Chains accumulate at the soft surface

Density shows a deficit beyond surface roughness

Depletion potential amplitude increases with surface fluctuations

Abstract

We investigate excluded-volume effects in a bidisperse colloidal suspension near a flexible interface. Inspired by a recent experiment by Dinsmore et al. (Phys. Rev, Lett. 80, 409 (1998)), we study the adsorption of a mesoscopic bead on the surface and show that depletion forces could in principle lead to particle encapsulation. We then consider the effect of surface fluctuations on the depletion potential itself and construct the density profile of a polymer solution near a soft interface. Surprisingly we find that the chains accumulate at the wall, whereas the density displays a deficit of particles at distances larger than the surface roughness. This non-monotonic behavior demonstrates that surface fluctuations can have major repercusions on the properties of a colloidal solution. On average, the additional contribution to the Gibbs adsorbance is negative. The amplitude of the depletion potential between a mesoscopic bead and the surface increases accordingly.