Study On Generation And Breakup Of Liquid Metal Droplets In T-junction Micro-channels

Microfluidic technology is a new interdisciplinary subject involving physics,biology,medicine,chemical engineering,microelectronics and other fields.There are several characteristics like quick reaction,high sensitivity,low cost and so on,which attract the attentions of many researchers.Micro-droplets prepared in the droplet-based microfluidic system have already been developed as different kinds of functional microreactors,which efficiently avoids cross contamination between different carriers.Hence,there are great development potential and promising applications of micro-droplets in drug delivery,human tissue engineering and other important areas.In order to generate micro-droplets owning much more plastic shapes,we choose a material showing extraordinary talents called“functional life”in recent years—liquid metal,which is totally different from traditional water-oil materials used for micro-droplets generation.First,we summarize the national and international recent developments of microfluidic technology.The generation and breakup of water-oil droplets(bubbles)and liquid metal droplets in different geometric microchannels are also introduced.Then,several dominating dimensionless parameters,the flow features of the two-phase flow and the dynamic mechanisms of droplet generation in three typical structures are briefly described in the following sequence.In this paper,The generation of liquid metal droplets in a T-junction is studied.Due to both the large surface tension of the liquid metal and the extra mechanical stability offered by the oxide layer,the collected droplets(axiolitic and spherical)owning good monodispersity and will not coalesce for a long time without any surfactant.Then,three factors including the viscosity of the continuous phase,the flow rate of continuous phase Q_c and the flow-rate ratio R(Q_c/Q_d)influencing the length of long axis(LA)and the short axis(SA)of the axiolitic droplets are systematically analyzed,and it is found that the length of LA has a linear relation with Q_c and an exponential relation with R.Finally,a general size prediction formula including both Q_c and R is fitted.As for the length of SA,it is almost independent with Q_cor R.With increasing the viscosity of the continuous phase,the droplet size decreases,and the axiolitic droplets transform into spherical droplets earlier in a lower Q_c.However,the whole changing tendency of the length of SA with Q_c and R is basically consistent.Forthermore,according to the size distributions and the corresponding simples,the relations among the viscosity of the continuous phase,the oxide layer and the stability of the liquid metal droplets are speculated.Next,some improvements are made on the former T-junction micro-chip,and the breakup of liquid metal droplets in this new micro-chip is achieved.The relations among the number and size of daughter droplets,the flow rate of the outer phase Q_oand the size of mother droplets are discussed systematically.It is found that when the number of daughter droplets is increasing,there is a power law between the size of spherical daughter droplets and Q_o.Fortunately,this size prediction formula is in agreement with the conclusions of the oil-water droplets.In conclusion,regardless of droplet generation or breakup,The controlling ability on the droplet rheological behavior and the droplet size distribution of these two kinds microfluidic chips designed in this paper are both satisfactory.