Liquid Crystals in Novel Geometries Prepared by Microfluidics and Electrospinning

Abstract

We describe two new techniques of preparing liquid crystal samples and discuss their potential for novel research and applications. Very thin polymer composite fibers functionalized by a liquid crystalline core are realized by coaxial electrospinning of a polymer solution surrounding the liquid crystal during the spinning process. The resulting fiber mats exhibit the special properties and responsiveness of the liquid crystal core, e.g. temperature dependent selective reflection when a short-pitch cholesteric is encapsulated. In the second approach an axisymmetric nested capillary microfluidics set-up is used to prepare liquid crystalline shells suspended in an aqueous continuous phase. The spherical geometry of the shell imposes specific defect configurations, the exact result depending on the prevailing liquid crystal phase, the director anchoring conditions at the inner and outer surfaces, and the homogeneity of the shell thickness. With planar director anchoring a variety of defect configurations are possible but for topological reasons the defects must always sum up to a total defect strength of s = +2. Homeotropic anchoring instead gives a defect-free shell, in contrast to a droplet with homeotropic boundary conditions, which must have a defect at its core. By varying the inner and outer fluids as well as the liquid crystal material and temperature, the defect configuration can be tuned in a way that makes the shells interesting e.g. as a versatile colloid crystal building block.

Acknowledgments

We thank Liang-Yin Chu for very kind advice regarding the construction of the microfluidic set-up and Enzo Calò for assistance with the electron microscopy investigations. Financial support from the Advanced Institutes of Convergence Technology, Korea, is gratefully acknowledged.