Flow of polymer blends—Developing a deformation-induced morphology followed by analytical scanning electron microscopy

Abstract

We applied a new experimental method for studying the evolution of the morphology in the flow of polymer blends. This so-called analytic scanning electron microscopy is based on spectroscopy of Auger electron transitions, which is widely used for catching foreign atoms in metals, alloys, and ceramic articles but has remained unknown in polymer science. The possibility of applying this approach to polymer blends became possible when choosing two polymers that are composed of different atoms. We have used polysulfone with sulfur in the main chain and a thermotropic liquid crystalline copolymer (LCP) of polyethylene terephthalate and p-hydroxybenzoic acid, which has significantly more oxygen atoms in its composition than polysulfone. In addition, LCP has lower viscosity. The blends with different ratios of components were extruded through a capillary at different shear rates. The components are randomly distributed, and no significant changes in the spatial distribution or the radial migration over the volume were observed during the low shear deformations. At high shear rates, phase separation takes place, emulsification of dispersed droplets of a low-viscous phase occurs, and these droplets were drawn along the streamlines, forming a self-arranged bundle of the strings. The increase in the radial transfer, leading to the phase separation, is most likely determined by the deformations and not by the shear rate. If the concentration of the low-viscous phase is high enough, it squeezed out of the extrudate body, forming a coverlayer on the convergent stream at the capillary inlet. The apparent viscosity of the blend strongly depends on the concentration of the low-viscous component. This can be explained by the combination of the predominant flow inside low-viscous strings and the existence of the low viscous “lubricant” on the periphery of the stream. The structure of the blend is destroyed at sufficiently high deformation rates apparently due to the emergence of the elastic turbulence.