Controlled Encapsulation of Cholesteric Liquid Crystals Using Emulsion Templates

Abstract

Cholesteric liquid crystals (CLCs) are nematic liquid crystals whose molecular orientation is periodically rotated by a chiral dopant. As the helical nanostructure has the spatial modulation of refractive index, CLCs have photonic stop band along the helical axis. The wavelength for the stop band is easily controllable by external stimuli, such as magnetic and electric fields, light, and temperature as the CLC molecules are highly mobile, enabling the use of the CLCs in various optical applications. However, the CLCs are fluidic, which restricts the ease of processing and structural stability. To overcome the limitations while maintaining the stop band tunability, the fluidic CLCs have been encapsulated by a solid membrane utilizing emulsion templates. This article reviews the encapsulation technologies and applications of CLC microcapsules. We first discuss optical property of CLCs and the influence of external stimuli and molecular alignment on the property. Afterward, we describe various methods for shell formation on the surface of CLC drops in bulk emulsification processes. Recent advances in the droplet microfluidics have provided elaborate control over CLC microcapsules, which is highlighted with a few key contributions. We discuss four representative applications of CLC microcapsules, which are displays, anti-forgery materials, colorimetric sensors, and lasing resonators. Finally, we outline the current challenges and outlook on the encapsulation technologies and applications.