Microdroplet formation in a t-junction with xanthan gum solutions

The T-junction microchannel device provides a sharp edge to generate microdroplets from polymeric solutions. Different concentrations of xanthan gum solutions were employed as dispersed phase and were compared with Newtonian reference. Canola oil, paraffin oil, and silicone oils (with viscosities varied from 65 to 500 cP) were used for the continuous phase. Experimental results showed that increasing the dispersed phase viscosity resulted in decreasing droplet size for the Newtonian fluids but increasing droplet size for the xanthan gum solutions. Two critical concentrations (0.15% and 0.3%) of xanthan gum solutions were observed resulting in three distinct regimes. The droplet diameter increased with increasing xanthan gum concentration within each regime but transition through each critical concentration was accompanied by a significant reduction in droplet size. For both Newtonian and non-Newtonian dispersed phases, smaller droplets were generated by a higher continuous phase viscosity (muc). A continuous phase with a viscosity around 200 cP was found to result in the minimum drop size distribution. Two critical continuous phase flow rates (2.5 and 7.5 ml/h) were identified that separated the result into three droplet formation regimes - squeezing, transition and dripping. The droplet formation mechanism for each regime is discussed in the paper.