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The effects of annealing and shear flow on texture growth, mechanical properties, and isotropization temperature in thermotropic liquid crystalline polymers
Abstract
The effect of annealing and shear deformation on the microstructure change, mechanical properties change, and nematic liquid crystalline to isotropic phase transition temperature, has been studied with two thermotropic liquid crystalline polymers (TLCPs). Homologous TLCPs, poly (p-(methylphenylene sulfonyl)-p-phenylene-1,10-decamethylene-bis(4-oxybenzoate)) and poly (p-(phenylene sulfonyl)-p-phenylene-1,10-decamethylene-bis(4-oxybenzoate)) were chosen for this study. The average schlieren line spacing (d) measured by POM was almost equivalent to q$\sb{\rm max}\sp{-1}$ measured by SALS. After a quench from the isotropic into the nematic state, the initial d and q$\sb{\rm max}\sp{-1}$ were almost independent of annealing temperatures. The annihilation rate of schlieren lines (coarsening) was time and temperature dependent. To describe the coarsening mechanism, a simple phenomenological rate model was adopted and compared with experimental results. The rate constant showed WLF type temperature dependence. The mechanical properties such as G$\sp\prime,$ G$\sp{\prime\prime},$ G$\sp*,$ $\eta\sp*,$ and tan $\delta$ remained almost identical up to 20 hrs annealing time though the schlieren texture changed during annealing. However nematic-smectic phase transition was observed in the long time annealing. After about 30 hrs annealing at 130$\sp\circ$C the LCP showed gel like behavior measurements. The long time annealed LCP showed a clear inner ring in the small angle x-ray scattering and the isotropization enthalpy was increased from DSC measurements. Anisotropic samples were produced to measure the directional dependence of mechanical properties. The samples were first sheared at constant rates and then G$\sp\prime$ and G$\sp{\prime\prime}$ were measured in the directions of shear and normal to the preshearing direction. The dynamic mechanical properties, G$\sp\prime$ and G$\sp{\prime\prime},$ decreased in shearing direction while they remained almost unchanged when probing normal to the presheared deformation direction. Annealing and shear deformation effects on the nematic-isotropic phase transition temperature (T$\sb{\rm i})$ were also observed by transmitted light intensity measurements. T$\sb{\rm i}$ increased with annealing time and temperature. The shear deformation also increased the nematic-isotropic phase transition temperature due to the macroscopic anisotropy increment. As strain increased, birefringence $(\Delta\sb{13})$ and isotropization transition temperature were also increased and reached a plateau at high shear strain deformations.
Subject Area
Chemical engineering|Plastics
Recommended Citation
Lee, Heung-Woo, "The effects of annealing and shear flow on texture growth, mechanical properties, and isotropization temperature in thermotropic liquid crystalline polymers" (1992). Doctoral Dissertations Available from Proquest. AAI9305855.
https://scholarworks.umass.edu/dissertations/AAI9305855