Parabolic effects of viscosity on dispersion and stability of millimeter-scale W1/O/W2 double droplets for ICF polymer shells

Abstract

Monodispersed poly(α-methylstyrene) (PAMS) microspheres using water-in-oil-in-water (W1/O/W2) composite double droplets as precursors are fabricated by microencapsulation. A rotating shear flow field where the droplets can be suspended is designed for the solidification. The stability and instabilities such as coalescence and aggregation of the double droplets during the solidification are studied. This work examines the effects of continuous phase viscosity on stability and dispersion of double droplets in a rotating shear flow field. Results show the continuous phase viscosity exerts a parabolic effect on stability of the double droplets. Experimental investigations combined numerical simulations have been conducted to discuss the mechanisms of this parabolic effect. Results show that coalescence occurs at lower continuous viscosity while aggregation occurs at higher continuous viscosity. Moreover, an increasing continuous viscosity promotes the collision between the droplets, leading an increasing aggregation between the droplets. In addition, the experimental investigations on the solidification show that the aggregation behavior always occurs in a percolation transition zone, where the oil phase concentration is 50–60%.