Interfacial tension controlled W/O and O/W 2-phase flows in microchannel

Abstract

In microfluidic systems, interfacial tension plays a predominant role in determining the two-phase flow behavior due to the high surface area to volume ratio. We investigated the influence of both solid–liquid (σ_SL) and liquid–liquid (σ_LL) interfacial tensions on water–oil two-phase flows in microfluidic devices. Experimental results show that, unlike macroscopic systems, σ_SL plays a dominant role, determining the emulsion type created in microchannels: oil-in-water (O/W) flow in hydrophilic microchannels and water-in-oil (W/O) flow in the corresponding hydrophobically treated microchannels. Modification of σ_LL by surfactants only plays a secondary role. By tuning σ_LL, oil–water two-phase flow patterns could be changed from droplet-based to stratified flows under constant flow conditions in the same device. In addition, also droplet deformation, coalescence and emulsion inversion could be achieved by tailoring σ_SL and σ_LL in microfluidic devices. Microfluidic technology therefore provides a valuable additional tool for quantitatively manipulating and evaluating these phenomena which are difficult to realize in the macroscale devices.