A Landau-de Gennes theory for hard colloidal rods: defects and tactoids

TL;DR

This paper develops a Landau-de Gennes theoretical framework for hard colloidal rods, accurately describing phase transitions, defect structures, and tactoid formations by fitting to Onsager theory results.

Contribution

It introduces a phenomenological Landau-de Gennes model for hard rods, capturing phase behavior and defect structures with parameters fitted to Onsager theory.

Findings

Successfully describes isotropic-nematic phase transition including density jump

Models isotropic-nematic planar interface accurately

Analyzes defect core sizes and tactoid formations

Abstract

We construct a phenomenological Landau-de Gennes theory for hard colloidal rods by performing an order parameter expansion of the chemical-potential dependent grand potential. By fitting the coefficients to known results of Onsager theory, we are not only able to describe the isotropic-nematic phase transition as function of density, including the well-known density jump, but also the isotropic-nematic planar interface. The resulting theory is applied in calculations of the isotropic core size in a radial hedgehog defect, the density dependence of linear defects of hard rods in square confinement, and the formation of a nematic droplet in an isotropic background.