Critical Casimir interactions between Janus particles

TL;DR

This paper investigates the critical Casimir forces between Janus particles and substrates, providing theoretical calculations and approximations to understand their interactions for potential self-assembly applications.

Contribution

It introduces a modified Derjaguin approximation for calculating critical Casimir forces involving Janus particles and compares it with mean field theory results.

Findings

Modified Derjaguin approximation is reliable for Janus particle interactions.

Calculated effective forces and potentials for Janus cylinders and spheres.

Demonstrated temperature-sensitive control of interactions.

Abstract

Recently there is strong experimental and theoretical interest in studying the self-assembly and the phase behavior of patchy and of Janus particles, which form colloidal suspensions. Although in this quest a variety of effective interactions have been proposed and used in order to achieve directed assembly, the critical Casimir effect stands out as being particularly suitable in this respect because it provides both attractive and repulsive interactions as well as the potential of a sensitive temperature control of their strength. Specifically, we have calculated the critical Casimir force between a single Janus particle and a laterally homogeneous substrate as well as a substrate with a chemical step. We have used the Derjaguin approximation and compared it with results from full mean field theory. A modification of the Derjaguin approximation turns out to be generally reliable. Based on this approach we have derived the effective force and the effective potential between two Janus cylinders as well as between two Janus spheres.