Thermodynamics and phase behavior of the lamellar Zwanzig model

TL;DR

This paper investigates the thermodynamics and phase behavior of binary lamellar colloids modeled as restricted-orientation platelets, revealing phase transitions and segregation phenomena using advanced density functional theory.

Contribution

It introduces a generalized Zwanzig model for lamellar colloids with three orientations and applies Rosenfeld's FMT to analyze phase behavior.

Findings

One-component model shows isotropic to nematic transition.

Transition narrows with increasing aspect ratio.

Binary mixtures exhibit complex phase segregation.

Abstract

Binary mixtures of lamellar colloids represented by hard platelets are studied within a generalization of the Zwanzig model for rods, whereby the square cuboids can take only three orientations along the $x$, $y$ or $z$ axes. The free energy is calculated within Rosenfeld's ''Fundamental Measure Theory'' (FMT) adapted to the present model. In the one-component limit, the model exhibits the expected isotropic to nematic phase transition, which narrows as the aspect ratio $\zeta=L/D$ ($D$ is the width and $L$ the thickness of the platelets) increases. In the binary case the competition between nematic ordering and depletion-induced segregation leads to rich phase behaviour.