Statistical mechanics of a colloidal suspension in contact with a fluctuating membrane

TL;DR

This paper provides an exact analysis of how thermal membrane fluctuations influence the static organization and effective interactions of colloids near a fluctuating membrane, revealing entropic attraction and implications for suspension stability.

Contribution

It derives exact results for colloid distribution and interactions near a fluctuating membrane, highlighting the entropic origin of effective attractions and their dependence on membrane properties.

Findings

Membrane fluctuations broaden colloid density profiles.

Colloids are neither accumulated nor depleted on average near the membrane.

Effective pair potential is always attractive with a range set by membrane correlation length.

Abstract

Surface effects are generally prevailing in confined colloidal systems. Here we report on dispersed nanoparticles close to a fluid membrane. Exact results regarding the static organization are derived for a dilute solution of non-adhesive colloids. It is shown that thermal fluctuations of the membrane broaden the density profile, but on average colloids are neither accumulated nor depleted near the surface. The radial correlation function is also evaluated, from which we obtain the effective pair-potential between colloids. This entropically-driven interaction shares many similarities with the familiar depletion interaction. It is shown to be always attractive with range controlled by the membrane correlation length. The depth of the potential well is comparable to the thermal energy, but depends only indirectly upon membrane rigidity. Consequenses for stability of the suspension are also discussed.