Shape-dynamic growth, structure, and elasticity of homogeneously oriented spherulites in an isotropic/smectic-A mesophase transition

TL;DR

This study uses a Landau-de Gennes model to simulate the growth and morphology of smectic-A spherulites in an isotropic matrix, revealing an undulation instability and mechanisms for defect formation.

Contribution

It introduces a detailed simulation of spherulite growth incorporating complex order parameters and identifies a new instability mechanism affecting defect formation.

Findings

Equal nematic splay-bend elasticity reproduces experimental observations.

Discovered an undulation instability during spherulite growth.

Proposed mechanisms for focal conic defect formation and smectic-A structures.

Abstract

A Landau-de Gennes model that integrates the nematic quadrupolar tensor order parameter and complex smectic-A order parameters is used to simulate the two-dimensional growth of an initially homogeneous smectic-A spherulite in an isotropic matrix. These simulations are performed in the shape-dynamic (nano-scale) regime of growth under two material conditions: isotropic nematic elasticity and equal splay-bend nematic elasticity. A comparison of the growth kinetics, spherulite morphology, interfacial/bulk energy landscapes between both cases is made showing that equal nematic splay-bend elasticity is required to reproduce past experimental and theoretical observations. Additionally, a previously unknown undulation instability during spherulite growth is found which, in conjunction with preferred planar anchoring and defect shedding mechanisms at micron length scales, could explain the formation mechanism of focal conic curvature defects and ultimately smectic-A "batonnet" structures observed experimentally.