SELF-ASSEMBLY OF BUBBLE SWARM IN LARGE CAVITIES IN STEP-TYPE PARALLELIZED MICROCHANNELS AND ITS FEEDBACK ON BUBBLE FORMATION

Step-emulsification microfluidic devices attract attentions due to the ability for the high-throughput production of bubbles and droplets. In this study, the bubble behavior of the bubble swarm in the cavity in a step-type parallelized microchannel and its feedback effect on bubble formation were studied by using a high-speed camera. The operating variables were the position of gas/liquid phase inlet, gas flow rate and liquid flow rate. Two bubble generation modes were observed: single-tube generation mode and multi-tube generation mode. The variation trend of the complex behavior of bubble swarm in the cavity with operating conditions was studied. It is found that in the confined space, the bubble can be self-assembled into a two-dimensional lattice with geometric features in the horizontal plane: including an ordered row triangular lattice, an ordered vertical triangular lattice, and a disordered triangular lattice. As the gas pressure changes, the crystal lattice changes, the bubble surface area becomes larger, and the interfacial energy becomes larger. Then, the effects of complex behavior of bubble swarm on bubble generation were analyzed by using the concepts of mesoscale, energy and activation. These fully explain the mesoscale characteristics of bubble behavior in confined spaces. The determinants of the bubble self-assembly path are revealed. It is indicated that the self-assembly path of bubbles is determined by the size and distribution of bubbles. The coefficient of variation of CV is used to represent the crystal structure of bubbles, and the coefficient of variation for the ordered triangular lattice is less than 5%, while that for the disordered triangular lattice is greater than 5%.