Formation of Uniform Plugs and Monodispersed Droplets for Viscoelastic Fluid Flow in Microchannels

In this paper we demonstrate for the procedure of passively cutting viscoelastic fluids into droplets with thin ligaments in an especially-designed microchannel with T-junction inlets, serpentine mid-part and an expansion end-part. The aqueous CTAC/NaSal solution of 50ppm and 100ppm were used as dispersed phase, pinched into uniform plugs at T-junction (100μm wide, 58μm deep) and then carried by silicone oil, towards downstream where the geometric expansion helped the plugs to form rounded droplets. Both squeezing and jetting regime were observed at Capillary number of 2.31 x 10^–3 and 4.61 x 10^–3 respectively. As experimental results shown, the filaments (thin threads) between plugs always existed until the plugs flew into the expanded pocket (400μm wide, 58μm deep), making surface tension initiate the plugs' profile to shrink, promoting the thinned threads breaking. In addition, it was also shown that the breakup and coalescence process for viscoelastic fluid was distinct form that for Newtonian fluid.