Microfluidic dissolution of nanoemulsions in solvents

Abstract

We experimentally investigate the behavior of nanoemulsion and microscale emulsion jets flowing in solvents using coaxial microfluidic devices. The stability of colloidal dispersions made of oil droplets dispersed in water is significantly altered by the presence of a miscible solvent, which induces complex solutal and droplet coalescence instabilities over various timescales. We reveal intriguing microflow patterns of oil-in-water micro- and nanoemulsion threads in a continuous phase of isopropanol, including the dissolving, diffusive, gravitational, and stable thread regimes. We discuss the evolution of core-annular flow characteristics and develop scaling relationships to model thread dynamics through measurements of effective diameter as well as persistence and gravitational lengths. A microflow method based on dynamic similitude is developed to estimate the diffusion coefficients of nanoemulsions and microscale emulsions in miscible solvents. This work shows the possibility to process soft colloidal dispersions and control degradation mechanisms using microfluidic techniques.