Study of phase behavior and (meta)stability of model surfactant solutions by microfluidic thermal fluctuation platform

Metastability poses considerable challenges for the practical utilisation of surfactant solutions subjected to ubiquitous temperature fluctuations. We first investigate aqueous solutions of a model biodegradable surfactant system (Linear Alkylate Sulfonate, LAS) at low concentrations, examining the mechanism and kinetics of the transition from micellar to multilamellar vesicle (MLV) phase, in the absence of salt and external flow. We then employ a novel microfluidic platform designed to rapidly modulate temperature fields and detect phase changes, coupled with optical microscopy and small angle neutron scattering (SANS). We resolve the MLV structure and decouple the nucleation and growth kinetics across the metastable zone width by imposing the square-wave temperature profiles. Finally, we demonstrate the imposition of complex temperature profiles, mirroring diurnal and seasonal variations, and their consequences to LAS micellar solution stability.