Phase-field simulations of morphology development in reactive polymer blending

Abstract

Reactive blending is an efficient method for synthesizing polymer blends. Industrially, this process is carried out in extruders, where the reacting polymers and the generated copolymer are subjected to high shear stresses. The dynamics of the process, and the resulting morphology is dictated by a coupling of the hydrodynamic forces in the extruder, the thermodynamic interactions between species, and the reaction kinetics on a complex interfacial manifold. We use phase-field simulations to quantify the evolution of the reactive blending process under an external shear flow. Specifically, we consider a model system of two homopolymers of equal length, which react via an end-coupling reaction to form a diblock copolymer of double the length. We compare the morphology development in two different initial geometries of the homopolymers—a cylindrical thread and a drop of one homopolymer in a matrix of the second. We investigate the effect of flow strength, measured by the shear rate, and reaction kinetics, quantified by a Damkohler number, on the progress of the reaction and morphology development. Cylindrical threads are susceptible to breakup via the Rayleigh capillary instability. We demonstrate that this instability can be suppressed by imposing shear along the direction of the thread and increasing the extent of the reaction. The reaction rate in this geometry is unaffected by shear imposed along the cylinder axis. Drops deform significantly under an imposed flow, eventually stretching to long cylindrical threads for sufficient shear rates. In the case of drops, shear stresses enhance the reaction rate by deforming the drop, enabling more homopolymers to come in contact at the expanded interface. We show that shear stresses significantly impact the morphology development and reaction dynamics in reactive polymer blending.