In this work, experiments were carried out to investigate the effects of viscosity ratio and interfacial tension on droplet formation within a microfluidic T-junction. Three liquid/liquid systems with different properties were considered, including water and two different concentrations of dextran solution as the dispersed phase as well as n-hexane as the continuous phase. Transition regime and dripping regime were detected in the experiments. Results showed that increasing the interfacial tension has an increasing effect on the size of droplets, while increasing the viscosity ratio (dispersed phase viscosity over continuous phase viscosity) has a decreasing effect on the size of droplets. The effects of the continuous phase flow rate, flow rate ratio, and capillary number on the droplet size and formation time were investigated. Also, droplet size distribution was presented to compare a system with a high viscosity ratio with a system with a low viscosity ratio. Using dextran solutions as dispersed phase leads to high viscosity ratios in dextran/hexane systems and there are a few works which focused on liquid/liquid systems with high viscosity ratios. So, the results of this study would be helpful for future studies on systems with high viscosity ratios.
