Researches On Liquid-liquid Two Phases And The Breakup Of Droplets In Cross-focusing Microchannel

The study of liquid-liquid two-phase flow behavior in microfluidic was of crucialimportance. In this paper, the generation of droplet by two phases was studied inmicrofluidic chip with cross-junction made of PDMS. In the process of generatingdroplet, the lengths of the head and the neck of the droplet were described. Next, thefactors that influence the droplet formation process and two phase flow types, the sizeof the droplet were discussed. It could be concluded as follows: in PDMS materials,two phase flow can be broken more easily than in PMMA and could obtain dropletflow and jetting flow; Adding surfactants can change the type of generated droplets—from W/O to O/W; Larger droplet with dripping regime would be obtained in thesystem of hexadecane and water, which was more suitable for studying two-phasebehaviors. Unusual results were obtained when ethanol was used as diepersed phaseinatesd of water, which was analysed simplely in this paper.Emulsion breakup makes an important role in the process of emulsionpolymerization reaction. But it was difficult to achieve this situation in the practicalexperimental conditions and an approximate experiment—the breakup of slugs wasapplied to study it. In this system, slugs were generated at the first intersection andthen were broken up by injecting continuous phase at the second intersection. A slugcould be split into numbers of daughter droplet due to the flow-focusing. Schemes ofthe splitting performance showed that more daughter droplet was obtained underlarger and shorter generation time slug. Higher Q3would help produce more daughterdroplet, too. Surfactants added in both generation and splitting continuous phasesinduce the breakup process and form more daughter droplets. These results revealedthat the rheological properties of the two phases have significant effects on thebreakup of slugs in such micro-devices.The relation between the flow rate and generated droplets size was used to analysethe relationship between the daughter droplet size and the flow rate during thebreakup process and the results were very similar, which meaned that the twoprocesses had some common feasures. But there were also differences between them:the produced droplet size was uniform in the process of generating droplet, which wasthe advantage of producing droplets in microfluidic devices; while in the process ofbreakup, each size of daughter droplet obtained by the breakup of slugs was different and became smaller gradually, which meaned that the subsequent fracture process wasinfluenced by previous fracture.