Phase Behavior in Thin Films of Confined Colloid−Polymer Mixtures

Using self-consistent-field and density-functional theories, we first investigate colloidal self-assembly of colloid−polymer films confined between two soft surfaces grafted by polymers. With increasing colloidal concentrations, the film undergoes a series of transitions from disordered liquid → sparse square → hexagonal (or mixed square-hexagonal) → dense square → cylindrical structures in a 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.