Flow induced morphological transitions in polymer blends containing a liquid crystalline polymer

Immiscible blending of polymers is a method to tailor polymeric materials to have specific properties, which sometimes can exceed those of the pure components. Introducing a thermotropic liquid crystalline polymer (TLCP) into a thermoplastic matrix can lead to anomalous viscosity reductions and microfibrillation, the latter of which may introduce novel solid material properties. Understanding and controlling these phenomena is of both scientific and technological interest.; In this work the coupling between shear flow and morphology has been characterized for three immiscible TLCP-based blend systems through a combination of rheology, X-ray scattering, and optical and scanning electron microscopy. In particular, the processing conditions and materials properties that control the onset of microfibrillation and viscosity reduction in these blends, as well as the specific role of the TLCP phase, have been studied.; The blends' rheology was found to be strongly dependent on the concentration and state of the TLCP. Large viscosity reductions were observed, which for some blends were anomalous (i.e. blend viscosities below those of either component). The microstructural characterization demonstrated that microfibers were formed at large shear stresses, and that these fibers remained stable within the processing time. This fiber stability was linked to a high degree of order in the TLCP phase.; The experimental results enabled testing of immiscible blend criteria for the blend rheology and microstructure. It was found that the droplet-fiber transition in these blends is determined by the balance of the mismatch of the elasticity between components and the interfacial tension. Thus, these unique behaviors of TLCP containing blends can be attributed to the unusual rheological properties of TLCPs.; A new constitutive equation for the blends' rheology is presented and tested here. It is based on the model proposed by Doi and Ohta, modified to include the viscoelasticity of the components. The rheological predictions of the model are reasonable for blends showing "regular" rheology. However, it fails to predict the anomalous viscosity reduction phenomenon with physically realistic parameters, and greatly underestimates the characteristic size of the dispersed phase. The modeling effort indicates that decoupling the flow kinematics from the evolution of the morphology is a poor assumption for these rheologically complex materials.