Rheology and morphology of polymer blends containing liquid crystalline polymers

The evolving morphology in immiscible polymer blends containing a liquid crystalline polymer (LCP) is coupled to the unique rheology of the LCP phase. Two LCP blend systems are investigated: a model lyotropic LCP (hydroxypropyl cellulose, HPC in H{dollar}sb2{dollar}O) blended with a room temperature melt (polydimethylsiloxane, PDMS) and an industrial thermotropic polyester LCP (TLCP) blended with a high temperature engineering plastic (polybutylene terephalate, PBT).; The rheology and microstructure of the two pure LCPs are first studied. Both systems show similar rheological behavior characteristic of LCPs. The increasing order in the HPC system is followed under shear using Small Angle Neutron Scattering (SANS). The elongation viscosity of the TLCP is shown to exhibit significant strain hardening, with the order during the elongation being much higher than in shear flow (as measured by wide angle X-ray scattering); The morphology development in the model blend system is measured during steady-state shear flow using SANS. A new scattering model is developed to quantify the observed anisotropic scattering in terms of a prolate ellipsoid. This new SANS technique allows the stable distortion of the HPC inclusions to be measured; the measured distortion is much less than expected for equivalent Newtonian blends. The enhanced stability is qualitatively explained by including the effects of component elasticity. An enhanced transition to fibers in the HPC/PDMS system is followed using a slit flow visualization technique.; The morphology of the TLCP blend is followed by scanning electron microscopy, SEM, on capillary extrudates. The morphologies are compared in terms of the local stress, and the observed transition to fibers occurs at high values of stress.; The LCP phase is generalized as being more stable under shear than the equivalent Newtonian component. The transition to a fibril morphology also occurs at higher than expected stress values. A second more extreme transition based on effective interfacial tension is noted in the model blend, but not so in the TLCP blend. It is suggested that the propensity for LCPs to microfibrillate is related to the stability of the fibers during and after flow, both of which are strong functions of the LCP rheology.