In situ characterization by small angle light scattering of the shear-induced coalescence mechanisms in immiscible polymer blends

This work presents an in situ experimental investigation of the shear-induc ed coalescence mechanism in low concentration polymer blends (1%-10%). An o riginal sizing method based on small-angle light scattering and optical mic roscopy were used to determine the evolution of the drop size distributions as a function of time. In order to study the pure coalescence mechanisms, measurements were conducted according to a specific flow protocol. The infl uences of the shear rate, initial morphology, concentration of the polymer blend and phase inversion on the coalescence kinetics were investigated. Th e investigated. blends are mixtures of polydimethylsiloxane and polyisobute ne. The amount of Strain, the step-down rate ratio and the concentration sq uared are identified as relevant parameters to describe the coalescence kin etics. The dependence of the steady state drop sizes on the applied shear r ate is well described by a coalescence model considering partially mobile i nterfaces. (C) 1999 The Society of Rheology. [S0148-6055(99)01806-4].