Depletion induced demixing and crystallization in binary colloids subjected to an external potential barrier

TL;DR

This study uses molecular dynamics simulations to explore how an external potential barrier induces phase separation and crystallization in a binary colloidal mixture, revealing temperature-dependent diffusion behaviors.

Contribution

It demonstrates how depletion interactions under an external barrier lead to phase separation and crystallization, with detailed analysis of diffusion behavior changes.

Findings

Depletion interaction causes phase separation near the barrier.

Crystalline domains form at high volume fractions.

Diffusivity transitions from sub-Arrhenius to super-Arrhenius with increasing volume fraction.

Abstract

A binary colloidal mixture of unequal sizes, subjected to an external potential barrier, has been investigated using canonical ensemble molecular dynamics simulations. The attractive depletion interaction between the external barrier and larger species in the binary mixture causes the mixture to phase separate. At higher volume fractions, a pure phase of larger particles forms near the potential barrier, and the local density of this pure phase is high enough that a face centered cubic crystalline domain is formed at this region. This crystalline phase diffuses perpendicular to the external potential barrier. The temperature dependence of diffusivity of larger particles is non-Arrhenius and changes from sub-Arrhenius to super-Arrhenius as the volume fraction increases. This crossover from sub-Arrhenius to super-Arrhenius diffusion coincides with the crystalline formation near the potential barrier.