Formation of droplets of shear-thinning fluids in a step-emulsification microdevice with parallel microchannels

The influence of the rheological properties of complex fluids in a step-emulsification microdevice with parallel microchannels on the dynamics of liquid–liquid two-phase flow is yet unclear. In this paper, the effects of the shear-thinning characteristic of the dispersed phase in a step-emulsification microdevice with double microchannels on the process of droplet generation, fluid distribution, and uniformity of droplet generation are investigated through a high-speed camera. The shear-thinning and high-viscosity characteristics of the dispersed phase are decoupled by using an aqueous glycerol solution of equal viscosity as the control group, and the influence of the shear-thinning characteristic on liquid–liquid interface evolution is explored. The shear-thinning characteristic of the dispersed phase reduces the uniformity of fluid distribution between parallel channels, while the high-viscosity characteristic improves the fluid distribution. A semi-empirical prediction model for droplet size is formed by estimating the characteristic viscosity of shear-thinning fluids. Based on a pressure drop model within parallel microchannels, step-emulsification microdevices with parallel microchannels are suitable for high-throughput formation of monodisperse shear-thinning droplets.