Structural studies of polymers and polymer liquid crystals by X-ray scattering, thermal analysis and ellipsometric studies through polarized light microscopy

We have studied the phase transformation behavior and structure of binary polymer blends and polymer liquid crystalline materials, to understand the formation of long and short-range ordered structures. We investigated their crystallization, melting and liquid crystalline behavior using Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Scattering (WAXS), Modulated Differential Scanning Calorimetry (MDSC), Polarized Light Microcopy (PLM), and Scanning Probe Microscopy (SPM). Materials selected for the study were: (1) a miscible blend of semicrystalline poly(etheretherketone), PEEK, and noncrystallizable poly(etherimide), PEI; (2) an immiscible blend of poly(ethyleneterephtalate), PET, and liquid crystalline polymer, Vectra RTM; (3) a thermotropic liquid crystalline random copolyester HIQ-40; and (4) new biological collagen model peptides.; We explore the phenomenon of multiple melting endotherms seen through MDSC after thermal pre-treatment of PEEK/PEI blend at different crystallization temperatures. Multiple melting endotherms have several possible origins, including melting of several populations of crystals with different lamellar thicknesses, melting of different crystallographic forms, or melting and recrystallization of the same population of crystals. The location of the amorphous phase, whether it is interlamellar, interfibrillar or interspherulite is addressed, by comparing the total crystallinity of the sample obtained by DSC and the linear stack crystallinity obtained by SAXS. Also by the temperature dependence of the smaller thickness determined from the SAXS correlation function, we were able to assign it to the crystalline thickness of the lamellae.; We studied the effect of Vectra on the crystallization behavior of PET, and found that it slows the nucleation time for crystallization, and decreases the sample viscosity. By X-ray scattering and Differential Scanning Calorimetry and optical measurements we showed that the liquid crystalline component Vectra RTM does not have an induction effect, but on the contrary, it has inhibiting effect on the crystallization time of the poly(ethyleneterephthalate). This slowing of the processes of crystallization has different effects: (1) During isothermal crystallization, the slowing of the processes leads to perfection of the crystals, expressed in larger lamellar thickness; and, (2) During non-isothermal crystallization, the slowing of the process leads to crystallization at lower temperatures, which leads to formation of less perfect crystals. With optical methods we were able to detect the phase separation occurring in PET/VectraRTM blends.; We constructed a polarized light microscope, using voltage driven liquid crystal phase retarders as precision universal compensator. The instrument provides real-time spatially resolved images of retardance and azimuthal angle for optically anisotropic polymers. We demonstrated several applications including polymer samples drawn with high extension ratio, collagen model peptides, HIQ-40 and PET/VectraRTM blends, and preliminary results are presented.