Conclusion

Abstract

The work presented in this doctoral thesis spans several original findings about nematic liquid crystals and their dispersions in microfluidic environment. Microfluidic studies of ordered liquid crystalline materials have hardly been explored hitherto – either for fundamental investigations, or for applications based on LC flows. Most of the existing literature focuses on the flow of nematic LCs within very wide channels – or slits. Such investigations, in the opinion of the author, are ideal for characterizing the flow-director coupling. However, in most of the practical circumstances, we encounter channel flows: The width and depth of the channels are of similar order of magnitude. Consequently, the flow of nematogens within strict microfluidic confinements offers two interacting length scales, which can be tuned conveniently using soft lithography techniques. The present research was thus motivated by the absence of systematic investigations on nematic micro-flows in strict microfluidic confinements. The accessibility to soft lithography techniques provided a wide range of possibilities, both in terms of channel dimensions and channel geometries. Combined to it, the sensitive dependence of nematic liquid crystal (5CB) on surface properties and temperature, essentially provided the different sets of experimental parameters considered in this research work. The experimental observations have been analyzed by a combination of polarization optical microscopy and fluorescence confocal polarization microscopy. While particle tracking methods have been employed for flow speed measurements, dual-focus fluorescence correlation spectroscopy has been introduced in this thesis as a generic velocimetry tool for LC flows.