Precise Control of Lyotropic Chromonic Liquid Crystal Alignment through Surface Topography.

Yubing Guo,Hamed Shahsavan,Metin Sitti,Zoey S Davidson

doi:10.1021/acsami.9b12943

Abstract

Many emerging applications, such as water-based electronic devices and biological sensors, require local control of anisotropic properties. Lyotropic chromonic liquid crystals (LCLCs) are an exciting class of materials, which are usually biocompatible and provide uniaxial anisotropy through a director field but, to date, remain difficult to control. In this work, we introduce a simple strategy to realize an arbitrary orientation of LCLCs director field in two dimensions (2D). Our alignment strategy relies on surface topographical micro/nanostructures fabricated by two-photon laser writing. We show that the alignment of LCLCs can be: (a) precisely controlled with a remarkable pixel resolution of 2.5 μm and (b) patterned into an arbitrary 2D alignment (e.g., +2 topological defect) by a pixelated design and arrangement of micro/nanostructures. Using a similar strategy, we achieve a patternable homeotropic alignment of LCLCs with nanopillars. Finally, we demonstrate that a self-assembled three-dimensional alignment of LCLCs can be obtained due to the versatility of our alignment strategy. Our demonstration of LCLC director field control, which is not only straightforward to achieve but also compatible with other conventional micro/nanofabrication techniques, will provide new opportunities for the manufacturing of LC-based electronic and biological devices.

Highlights

Among various types of liquid crystals (LCs), lyotropic chromonic liquid crystals (LCLCs) are of special interest for biological and medical applications since many are nontoxic and compatible with living organisms.[1,2] LCLCs are composed of plank-like organic salt molecules, which self-assemble into elongated assemblies in solutions by attracting each other face to face.[3−5] At certain concentrations and temperatures, these assemblies form LC phases, which often include a nematic phase exhibiting a long-range uniaxial order along a so-called director field
We report a facile and robust technique to program localized, and arbitrary orientations of LCLCs director in two and three dimensions using topographical structures on the confining substrates
For the alignment of LCLCs in arbitrary patterns throughout a large area, we demonstrated pixelated designs of a +2 topological defect array and found that the pixel resolution limit of this alignment strategy is close to 2.5 μm, which is highly improved over other techniques reported in the literature

Summary

Introduction

Among various types of liquid crystals (LCs), lyotropic chromonic liquid crystals (LCLCs) are of special interest for biological and medical applications since many are nontoxic and compatible with living organisms.[1,2] LCLCs are composed of plank-like organic salt molecules, which self-assemble into elongated assemblies in solutions by attracting each other face to face.[3−5] At certain concentrations and temperatures, these assemblies form LC phases, which often include a nematic phase exhibiting a long-range uniaxial order along a so-called director field. Similar to devices based on thermotropic LCs, the fabrication of LCLC-based devices crucially depends on the well-controlled orientation of the LCLC assemblies. Uniform alignment of LCLCs enables their wide application in water-solution processable organic electronic devices,[6] inexpensive optical components,[7−10] biological sensors,[2,11−14] and template fabrication of nanopatterns.[15,16] In addition to uniformly aligned LCLC-based devices, spatially nonuniform patterned LCLCs facilitate emerging applications, such as bacterial assembly.[1,13] For example, LCLCs have been patterned into arrays of topological defects to direct motile bacteria distributions and their trajectories.[1]

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Conclusion