Numerical And Experimental Research Of Double Emulsion Formation In The Six-way Junction Microfluidic Chip

The six-way junction microfluidic chip has been widely used to fabricate double emulsions for microencapsulating cells.The microencapsulation effectively inhibit intracellular ice formation(IIF)during warming the vitrified cells at cryogenic temperature back to super-zero temperatures,and both the droplet diameters and shell thickness of double emulsions affect the effect of suppressing IIF.However,the influence factors of the droplet diameters and shell thickness of double emulsions still need to be further explored,and the double emulsion formation mechanisms at three typical flow regimes have not been revealed.Restricted by the measuring method,the experimental research provide the limited information of immiscible liquid flowing in the microfluidic chip.In this research,a numerical model based on the VOF method is presented for investigating double emulsion formation and shell thickness influence factors in the six-way junction microfluidic chip.Moreover,a new concept named relative shell thickness is proposed to intuitively reflect the relationship between the shell thickness and drop size.Results indicate that typical flow regimes of double emulsion formation in the six-way junction microfluidic chip could be classified into dripping,narrowing jetting,and widening jetting.Increasing the capillary numbers induces the flow regime transition from dripping to jetting.In dripping,the drop diameters and shell thickness exhibit slow downward trends as the capillary numbers increase.When the flow regime transits,both shell thickness and relative shell thickness increase abruptly.Varying the flow rate of the middle and outer fluid not only affect the flow regime but also the droplet diameters and shell thickness.The effect of middle fluid flow rate on the shell thickness,however,is larger than the flow rate of outer fluid.In addition,the double emulsions with thin shells are mainly formed in dripping.This paper reveals the change law of shell thickness with varied operation parameters and can guide for preparing double emulsions with controllable shell thickness in the six-way junction microfluidic device.In addition,the six-way junction microfluidic chip with optimized structure was fabricated by soft lithography.The microfluidic experimental platform was established to successfully prepare double emulsions.