Bubble formation in non-Newtonian fluids in a microfluidic T-junction

The aim of this work is to investigate the bubble formation in non-Newtonian fluids in a microfluidic T-junction by crossflowing rupture technique, using a high-speed digital camera. Experiments were conducted in a glass microchannel with 120 μm wide and 40 μm deep. N₂ bubbles were generated in different concentrations of polyacrylamide (PAAm) solutions. Various flow patterns were observed at the T-junction by varying gas and liquid flow rates. The breakup mechanism for bubbles was investigated to gain insight into the effects of flow rates and concentrations of PAAm solutions on bubble size. The gaseous thread collapses at a constant speed in the collapse stage; while during the final pinch-off stage, the variation of the minimum width W_m of the gaseous thread with the remaining time (T − t) could be scaled as W_m ∼ (T − t)^0.21. The bubble size increases non-linearly with the gas/liquid flow rates ratio, and decreases with the concentration of PAAm solutions.