OBSERVATION OF DEFORMATION AND RECOVERY OF POLY(ISOBUTYLENE) DROPLET IN A POLY(ISOBUTYLENE) POLY(DIMETHYL SILOXANE) BLEND AFTER APPLICATIONOF STEP SHEAR STRAIN/

The deformation and recovery of a poly(isobutylene) droplet with a low er viscosity embedded in a poly(dimethyl siloxane) matrix are directly observed from two directions after application of a large step shear strain. The droplet shape and recovery time strongly depended on the m agnitude of the applied strain. Just after application of a large stra in, a droplet deforms almost affinely to a flat ellipsoid. It then cha nges into a rodlike shape, a dumbbell, and to an ellipsoid of revoluti on, and finally to a sphere. Model calculations show that the primary driving force for the shape recovery is the interfacial energy in orde r to reduce the surface area of the deformed droplet. (C) 1998 The Soc iety of Rheology.