N2 bubble formation in highly viscous (630 mPa·s) glycerol-water solution in a microfluidic flow-focusing cross channel device was observed by using a high-speed camera. Bubble forming process
size
and minimal neck radius were studied. The results show that the bubble formation process can be divided into stages of retraction
expansion
collapse
and final breakup. The bubble size was increased linearly with time in both expansion and collapse stages
which the slope in the collapse stage was greater than that in the expansion stage. The decrease of minimal neck radius of bubbles against time was different in two stages
i.e.
a power-law to remaining time in the collapse stage and a linearity with time in the final breakup stage.