A flow-induced phase inversion in immiscible polymer blends containing a liquid-crystalline polymer studied by in situ optical microscopy

The phase inversion from a morphology of hydroxypropylcellulose in water (HPC50%) droplets in polydimethylsiloxane (PDMS) matrix to a morphology of PDMS droplets in HPC50% matrix can be induced by a change of shear rate, due to a viscosity ratio inversion. Such a process passing through four different transient morphological stages was studied by optical microscopy in a transparent shear device. In a certain concentration region, at a fixed shear rate, after sheets of PDMS were formed, the transition "hesitates" between phase inversion and refined starting morphology. The influence of PDMS concentration, shear rate, elasticity, and phase dimension on the final morphology was investigated and compared with different models given in the literature. The influence of concentration and shear rate on the duration of the transient flow was also studied. We propose a simplified model of breakage of filaments to explain a part of our results. (C) 2000 The Society of Rheology. [S0148-6055(00)01504-2].