Determining the Anchoring Strength of a Capillary Using Topological Defects

TL;DR

This paper investigates how surface anchoring and magnetic fields influence the formation of topological defects in a chiral smectic-A* phase within a capillary, providing a method to measure anchoring strength through critical field calculations.

Contribution

It introduces a theoretical framework to determine the anchoring strength by analyzing the critical magnetic field for defect formation in a capillary with chiral smectic-A*.

Findings

Critical radius below which no defects form.

Magnetic field suppresses screw dislocation formation.

Method to experimentally determine anchoring strength.

Abstract

We consider a smectic-A* in a capillary with surface anchoring that favors parallel alignment. If the bulk phase of the smectic is the standard twist-grain-boundary phase of chiral smectics, then there will be a critical radius below which the smectic will not have any topological defects. Above this radius a single screw dislocation in the center of the capillary will be favored. Along with surface anchoring, a magnetic field will also suppress the formation of a screw dislocation. In this note, we calculate the critical field at which a defect is energetically preferred as a function of the surface anchoring strength and the capillary radius. Experiments at a few different radii could thus determine the anchoring strength.