A novel droplet-based approach to study phase transformations in lyotropic liquid crystalline systems

Abstract

Hypothesis: Lyotropic liquid crystals (LLC) and their phase transformations in response to stimuli have gathered much interest for controlled and 'on-demand' drug applications. Bulk methods of preparation impose limitations on studying the transformations, especially induced by compositional changes, such as enzymatic changes to lipid structure. Here we hypothesise that controlled microfluidic production and coalescence of dissimilar aqueous and lipid droplets emulsified in a third mutually immiscible liquid will provide a new approach to the spatio-temporal study of structure formation in lyotropic liquid crystalline materials.

Experiments: Separate lipid and aqueous droplets, dispersed in a fluorocarbon oil were generated using a microfluidic format. The chip, prepared as a hybrid polydimethylsiloxane (PDMS) and glass microfluidic device, was constructed to enable in-situ acquisition of time-resolved synchrotron small angle X-ray scattering (SAXS) and crossed polarised light microscopy of the coalesced droplets to determine the structures present during aging.

Findings: Janus-like droplets formed upon coalesce, with distinct lipid and aqueous portions with a gradient between the two sides of the merged droplet. SAXS and polarised light microscopy revealed a progression of mesophases as the lipid portion was hydrated by the aqueous portion via the diffusion limited interface which separated the portions. Thus demonstrating, on a droplet scale, a new approach for studying the phase transformation kinetics and identification of non-equilibrium phase in droplet-based lyotropic liquid systems.

Keywords: Cubic phase; Emulsion droplet; Hexagonal phase; Lipid self-assembly; Microfluidic system; Monoolein; Small angle X-ray scattering.