Generation of all-aqueous emulsions and clogging in microchannels

Droplet-based microfluidics have enabled generation of oil-water emulsions of tunable size and structure. However, the use of oil-based solvents in the emulsion fabrication process necessitates tedious procedures for their complete removal before the resultant materials can be used in aqueous environments. To address this, all-aqueous emulsions, which are emulsions with dispersed and continuous phases of immiscible aqueous phases, have been proposed as an alternative. The different interfacial and rheological properties of these emulsion phases demand novel emulsion generation and stabilization strategies. In the first part of this talk, we will present recent approaches developed to prepare all-aqueous emulsions in microfluidic devices (Figure on left).

In the second part of the talk, we will consider the transport of solid particles in porous media. In this model experiment, a suspension of colloidal particles flows through a series of constrictions, i.e. a microchannel of varying cross-section (Figure on right). We show that the constrictions dramatically modify the flow of a diluted suspension of commercial colloidal particles generated by emulsion-polymerization. More specifically, we establish the role of large contaminants in the clog formation and the resulting formation of particle aggregates. This microfluidic setup composed of a single microchannel or an array of parallel channels suggests a simple way to evaluate the presence of large contaminants at ultra-low concentration.