Capillary-driven biaxial planar and homeotropic nematization of hard cylinders

TL;DR

This study uses a modified Onsager theory to analyze phase behavior of hard cylindrical rods in confined spaces, revealing various surface nematic phases and transitions depending on pore size and particle aspect ratio.

Contribution

It introduces a theoretical analysis of nematic phase transitions of hard cylinders in narrow pores, highlighting new surface anchoring behaviors and transition conditions.

Findings

Identification of multiple surface nematic phases including biaxial and monolayer structures.

Discovery of second order uniaxial biaxial transitions depending on particle aspect ratio.

Observation of surface anchoring transitions occurring at lower packing fractions than in previous models.

Abstract

We use the Parsons Lee modification of Onsagers second virial theory within the restricted orientation approximation to analyse the phase behaviour of hard cylindrical rods confined in narrow pores Depending on the wall to wall separation we predict a number of distinctly different surface generated nematic phases including a biaxial planar nematic with variable number of layers a monolayer homeotropic and a hybrid T type structure For narrow pores we find evidence of two types of second order uniaxial biaxial transitions depending on the aspect ratio of the particles More specifically we observe a continuous cross over from n to layers each with a distinct planar anchoring symmetry as well as first order transitions from planar to homeotropic surface anchoring Contrary to the previously studied case of parallelepipeds we find that the surface anchoring transition from planar to homeotropic symmetry occurs at much lower overall rod packing fractions