Self-Localized Liquid Crystal Micro-Droplet Arrays on Chemically Patterned Surfaces

Jakub Kołacz,Qi-Huo Wei

doi:10.3390/cryst12010013

Abstract

Liquid crystal (LC) micro-droplet arrays are elegant systems that have a range of applications, such as chemical and biological sensing, due to a sensitivity to changes in surface properties and strong optical activity. In this work, we utilize self-assembled monolayers (SAMs) to chemically micro-pattern surfaces with preferred regions for LC occupation. Exploiting discontinuous dewetting, dragging a drop of fluid over the patterned surfaces demonstrates a novel, high-yield method of confining LC in chemically defined regions. The broad applicability of this method is demonstrated by varying the size and LC phase of the droplets. Although the optical textures of the droplets are dictated by topological constraints, the additional SAM interface is shown to lock in inhomogeneous alignment. The surface effects are highly dependent on size, where larger droplets exhibit asymmetric director configurations in nematic droplets and highly knotted structures in cholesteric droplets.

Highlights

Due to their optical activity, Liquid crystal (LC) in confined geometries are important to a variety of current technologies
In polymer-dispersed LCs, micron-sized LC droplets are directed to either scatter or transmit light by altering the molecular orientation using an external electric field [1], a switching mechanism which has been utilized in smart windows [2]
We explored the ability of LC to self-localize via chemical pinning [10] on μ-contact printed surfaces [25] using two LC-philic inks by maximizing the disparity between static contact angles

Summary

Introduction

Due to their optical activity, LCs in confined geometries are important to a variety of current technologies. In polymer-dispersed LCs, micron-sized LC droplets are directed to either scatter or transmit light by altering the molecular orientation using an external electric field [1], a switching mechanism which has been utilized in smart windows [2]. Microfluidic devices that utilize LCs [7,8] are becoming popular because they can be incorporated into sensor networks or lab-on-a-chip systems, which are highly desirable for environmental science, forensics, biological warfare, and point-of-care diagnostics. Such devices need high sensitivity to target molecules, fast response to change, portable size, and must be economically and environmentally friendly

Methods

Results

Conclusion