Investigation of Structure-Property Relationships Between Crystal Orientation and Dielectric Behavior in Liquid Crystalline Polymers

Abstract

Liquid crystalline polymers (LCP’s) make up a class of high performance materials, which derive favorable mechanical, chemical, and electrical characteristics from their long-range molecular order. The unique LCP microstructure gives rise to anisotropic bulk behavior and an understanding of the driving forces behind this morphology is essential to the design of manufacturing processes for isotropic material production. In this investigation, the crystalline orientation in injection molded LCP plaque samples was measured using 2D wide-angle x-ray scattering (WAXS). The direction of preferred alignment was observed from the WAXS scattering patterns and the degree of orientation in the material was quantified using an order parameter and an anisotropy factor. In addition, the dielectric constant was measured with respect to the mold direction (MD) and transverse direction (TD). To investigate the effects of processing on hierarchal structure in the material, and the resulting macroscopic properties, plaques of two different thicknesses were analyzed, both as-injection molded and with the skin layer mechanically removed. It is shown that preferred orientation along the shear direction in the LCP samples corresponds to dielectric anisotropy, and increasing sample thickness, or conversely, mechanically removing the shear aligned layer, results in a more isotropic dielectric response.