Phase Behavior in Thin Films of Confined Colloid-Polymer Mixtures

TL;DR

This study uses theoretical models to explore how colloid-polymer mixtures confined between soft surfaces self-assemble into various ordered structures as concentration and surface properties change, revealing new control mechanisms.

Contribution

The paper introduces a theoretical framework for understanding and controlling the phase behavior of confined colloid-polymer films, highlighting new stabilization mechanisms for ordered structures.

Findings

Sequence of phase transitions with increasing colloidal concentration

Identification of stable in-layer ordering structures

Layering transitions influenced by polymer-grafted density

Abstract

Using self-consistent field and density-functional theories, we first investigate colloidal self-assembling of colloid/polymer films confined between two soft surfaces grafted by polymers. With the increase of colloidal concentrations, the film undergoes a series of transitions from disordered liquid $\to$ sparse square $\to$ hexagonal (or mixed square-hexagonal) $\to$ dense square $\to$ cylindric structures in plane, which results from the competition between the entropic elasticity of polymer brushes and the steric packing effect of colloidal particles. A phase diagram displays the stable regions of different in-layer ordering structures as the colloidal concentration is varied and layering transitions as the polymer-grafted density is decreased. Our results show a new control mechanism to stabilize the ordering of structures within the films.