Structure development in confined polymer blends: steady-state shear flow and relaxation

In this work, the structure development in immiscible polymer blends in confined geometries is systematically investigated. Poly(dimethylsiloxane)/poly(isobutylene) blends with a droplet-matrix structure are subjected to simple shear flows. The confined environment is created by using a Linkam shearing cell in which the gap is systematically decreased to investigate the transition from "bulk" behavior toward "confined" behavior. Small-angle light scattering experiments in a confinement, which have not yet been reported in the literature, and also microscopy are used to observe the morphology development during steady-state shearing and relaxation. These experiments indicate that the size and relaxation of single droplets in a confined environment are still governed by the relations that describe the structure development in bulk situations. Yet, depending on the applied shear rates and blend concentrations, the droplets organize in superstructures such as pearl necklaces or extended superstrings in a single layer between the plates. These structures are stable under flow. To observe a single layer, a critical ratio of droplet size to gap spacing is required, but this ratio is clearly below the one already reported in the literature.