Elementary edge and screw dislocations visualized at the lattice periodicity level in smectic phase of colloidal rods

TL;DR

This study visualizes and characterizes elementary edge and screw dislocations in a colloidal smectic phase at the lattice scale, providing insights into their structure, core size, and local ordering.

Contribution

It offers the first direct optical visualization of dislocations at the smectic periodicity in colloidal rods and compares experimental displacement fields with elastic theory.

Findings

Displacement field around edge dislocation matches elastic theory predictions.

Elementary screw dislocations with determined core size and handedness.

Defect cores exhibit nematic-like 'melted' ordering revealed by self-diffusion experiments.

Abstract

We report on the identification and quantitative characterization of elementary edge and screw dislocations in a colloidal smectic phase of tip-labeled rods. Thanks to the micrometer layer spacing, direct visualization of dislocations has been performed at the \textit{smectic periodicity scale} by optical fluorescence microscopy. As a result, the displacement field around an edge dislocation has been experimentally established and compared with the profile predicted by elastic theory. Elementary screw dislocations have been also evidenced, for which the core size as well as the \textit{in situ} handedness have been determined. Self-diffusion experiments performed at the individual particle level reveal for the first time nematic-like or "melted" ordering of the defect core.