Particle-resolved topological defects of smectic colloidal liquid crystals in extreme confinement

René Wittmann,Louis B G Cortes,Dirk G A L Aarts,Hartmut Löwen

doi:10.1038/s41467-020-20842-5

René Wittmann, Louis B G Cortes + Show 2 more

Open Access

https://doi.org/10.1038/s41467-020-20842-5

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Abstract

Confined samples of liquid crystals are characterized by a variety of topological defects and can be exposed to external constraints such as extreme confinements with nontrivial topology. Here we explore the intrinsic structure of smectic colloidal layers dictated by the interplay between entropy and an imposed external topology. Considering an annular confinement as a basic example, a plethora of competing states is found with nontrivial defect structures ranging from laminar states to multiple smectic domains and arrays of edge dislocations, which we refer to as Shubnikov states in formal analogy to the characteristic of type-II superconductors. Our particle-resolved results, gained by a combination of real-space microscopy of thermal colloidal rods and fundamental-measure-based density functional theory of hard anisotropic bodies, agree on a quantitative level.

Highlights

Confined samples of liquid crystals are characterized by a variety of topological defects and can be exposed to external constraints such as extreme confinements with nontrivial topology
These phases are highly susceptible to external topological and geometrical influences[2]. This opens a fascinating new research realm on the internal structural response to such externally imposed constraints with various highly relevant applications in technology and material science[3,4]. While these perspectives have been extensively exploited for spatially homogeneous mesophases, such as nematics, there is much yet undisclosed potential stemming from the complex interplay between external constraints and internal order emerging in more complex mesophases, such as the layered smectic phase
In doing so we study two-dimensional smectics composed of lyotropic colloidal rods whose size enables a direct observation[37,38,39], while they have the advantage over granulates[40,41] that they are fully thermally equilibrated

Summary

Introduction

Confined samples of liquid crystals are characterized by a variety of topological defects and can be exposed to external constraints such as extreme confinements with nontrivial topology. 1234567890():,; Liquid crystals consist of particles that possess both translational and orientational degrees of freedom and exhibit a wealth of mesophases with partial orientational or positional order such as nematic, smectic and columnar states[1] As such, these phases are highly susceptible to external topological and geometrical influences[2]. The colloidal samples are exposed to extreme confinements possessing an annular shape and dimensions of a few particle lengths This combination of curved geometry and nontrivial topology is triggering certain characteristic defect patterns. Our study explores the intriguing competition between the internal liquid crystal properties and the extrinsic topological and geometrical constraints In annular confinement this gives rise to three essential types of smectic defect configurations. A locally adaptable layer spacing is found here to play the key role regarding the stability and distribution of defect structures in extreme confinement

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