Tuning Molecular Orientation Responses of Microfluidic Liquid Crystal Dispersions to Colloid and Polymer Flows

Abstract

An important approach to molecular diagnostics is integrating organized substances that provide complex molecular level responses to introduced chemical and biological agents with conditions that optimize and distinguish such responses. In this respect, liquid crystal dispersions are attractive components of molecular diagnostic tools. This paper analyzes a colloid system, containing a nematic liquid crystal as a dispersed phase, and aqueous surfactant and polymer solutions as the continuous phases. We applied a microfluidic approach for tuning orientation of liquid crystal molecules in picoliter droplets immobilized on microchannel walls. Introduction of surfactant to the aqueous phase was found to proportionally increase the order parameter of liquid crystal molecules in microdroplets. Infusion of polymer solutions into surfactant-mediated microfluidic liquid crystal dispersions increased the order parameter at much lower surfactant concentrations, while further infusion of surfactant solutions randomized the orientation of liquid crystal molecules. These effects were correlated with the adsorption of surfactant molecules on surfaces of microdroplets, stabilizing the effect of a polymer matrix on bound surfactant ions and the formation of insoluble polymer–colloid aggregates, respectively. The revealed molecular behavior of liquid crystal dispersions may contribute to optimized synthesis of responsive liquid crystal dispersions for in-flow molecular diagnostics of polymers and colloids, and the development of functional laboratory-on-chip prototypes.

Molecular Orientation Behavior of Lyotropic Liquid Crystal–Carbon Dot Hybrids in Microfluidic Confinement

“…This work aims at studying the molecular orientation and related optical behavior of anisotropic luminescent media represented by composites of a lyotropic liquid crystal with nanoscale carbon dots. This study integrates and continues our previous research on lyotropic liquid crystals [44,45] and microfluidic optically active media [46,47]. We characterized the molecular orientation responses of static composites to both external and intrinsic microfluidic factors such as heating and cooling and wall effects.…”

“…The chip design is shown in Figure 2a. According to our previous works [46,47], such microchannels (100-300 µm wide) allow for obtaining high-quality POM images with easily distinguishable patterns of LC textures. The POM images of both the individual LLC and the composite (Figure 1) show characteristic patterns observed for lamellar lyotropic mesophases [57].…”

“…The chip design is shown in Figure 2a. According to our previous works [46,47], such microchannels (100-300 µm wide) allow for obtaining high-quality POM images with easily distinguishable patterns of LC textures. Macrophotography imaging of microfluidic channels filled with composite allowed for directly observing the luminescence of the composite in the microchannel.…”