Steady deformation characteristics of double emulsion droplet in shear flow

The manipulation of double emulsion droplet via shear flow field is widely encountered in microfluidic devices. However, the interface evolution and hydrodynamics behavior of double emulsion droplet in shear flow is less understood till now. In this paper, a theoretical model of double emulsion droplet in a Couette flow device is developed and numerically analyzed to characterize the interface behavior of incompressible double emulsion droplet, which is also verified by a visualization experiment. Based on this model, the mechanisms underlying the steady deformation of double emulsion droplet under shear are investigated, and the effects of radius ratio of inner droplet to the outer one and viscosities of working fluids on the steady deformation are discussed. The results indicate that the steady deformation of double emulsion droplet in the shear increases with the rise in capillary number, and the deformation resistance of inner droplet is larger than that of the outer droplet. With increasing the radius ratio of inner droplet to the outer one, the interaction between the inner and outer droplets becomes great and thus the deformation degree of the inner droplet is increased. In addition, the effect of big deformation resistance by the inner droplet tends to be obvious, leading to decreasing the deformation degree of outer droplet. The viscosities of both inner and outer droplets provide a resistance for the deformation of double emulsion droplet. With the rises in viscosities of inner and outer droplets, the deformation degree of integral double emulsion droplet decreases. In addition, the effect of outer droplet viscosity on the steady deformation is more obvious than that of the inner droplet.