Collective dynamics of colloids at fluid interfaces

TL;DR

This study uses Brownian dynamics simulations to analyze how colloidal particles trapped at fluid interfaces evolve under capillary attraction, revealing a crossover from logarithmic to exponential decay in interactions and a transition from spinodal decomposition to gravitational collapse.

Contribution

It adapts a cosmological particle-mesh algorithm to colloidal systems, providing new insights into the crossover of interaction decay and structure formation at fluid interfaces.

Findings

Confirmation of mean-field theory predictions

Observation of transition from spinodal decomposition to gravitational collapse

Identification of a crossover in interaction decay behavior

Abstract

The evolution of an initially prepared distribution of micron sized colloidal particles, trapped at a fluid interface and under the action of their mutual capillary attraction, is analyzed by using Brownian dynamics simulations. At a separation \lambda\ given by the capillary length of typically 1 mm, the distance dependence of this attraction exhibits a crossover from a logarithmic decay, formally analogous to two-dimensional gravity, to an exponential decay. We discuss in detail the adaption of a particle-mesh algorithm, as used in cosmological simulations to study structure formation due to gravitational collapse, to the present colloidal problem. These simulations confirm the predictions, as far as available, of a mean-field theory developed previously for this problem. The evolution is monitored by quantitative characteristics which are particularly sensitive to the formation of highly inhomogeneous structures. Upon increasing \lambda\ the dynamics show a smooth transition from the spinodal decomposition expected for a simple fluid with short-ranged attraction to the self-gravitational collapse scenario.