Investigation of liquid crystal polymer structure-property relationships between crystal orientation and dielectric behavior

Abstract

Liquid crystalline polymers (LCP's) make up a class of performance materials that derive favorable mechanical, chemical, and electrical characteristics from their long-range molecular ordering. This unique 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 preferred crystal orientation in injection molded LCP plaque samples was measured using wide-angle x-ray scattering (WAXS) and the degree of order in the material was quantified using an order parameter and an anisotropy factor. Additionally, the dielectric constant of the samples was measured with respect to the mold direction (MD) and transverse direction (TD). Specimens were analyzed both as-injection-molded and with the skin layer removed, to investigate the effects of hierarchal structure on material properties. It is shown that preferred orientation along the shear direction in the LCP samples corresponds to dielectric anisotropy, and mechanically removing the shear-aligned layer results in a more isotropic dielectric response.