Transient and steady state deformations of dispersed-phase droplets in immiscible polymer blends in steady state shear flow

Abstract

Transient deformation and breakup of viscoelastic polystyrene (PS) droplets dispersed in an viscoelastic high density polethylene (HDPE) matrix were observed under a simple steady state shearing flow between two transparent parallel disks. The influence of elasticity of the blend constituent components on the deformation and equilibrium size of dispersed-phase droplet was investigated. The viscosity ratios were fixed at 0.5, 1.0 and 2.6, After the startup of steady state shearing flow, the viscoelastic droplet shape initially showed small oscillations in the flow direction, after which its shape oscillated and deformed in the vorticity direction. The steady-state deformation of droplet in vorticity direction increased with increasing capillary number. When the critial capillary number, Cac, was exceeded, the droplet stretched and formed a string which became thinner and finally broke up. At a fixed capillary number, the deformation of droplet in the vorticity direction decreased with increasing droplet elasticity. When the capillary number and the Wessenberg number were kept fixed, the steady-state deformation in vorticity direction and the critical capillary number for breakup were found to increase as the viscosity ratio was varied from 0.5 to 1.0, and to 2.6.