Microfibrillar structures in liquid-crystalline polymers

Preliminary new observations that contribute to a more complete structural model for liquid crystalline polymers (LCPs) are reported. The LCPs investigated consisted of highly oriented fibers and tapes composed of copolyesters of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) and other related thermotropic polymers. The aramid fiber Kevlar was also investigated for comparison. Samples were prepared by peel back and ultrasonication. All LCPs studied were found to be composed of the same fibrillar building blocks arranged in a hierarchy reminiscent of biological systems such as collagen and cellulose. The microfibrils are tape-like in shape. Comparison of the molecular and microfibrillar sizes suggest that the microfibrils are composed of two to five molecules. The LCP structural model consisting of elongated well-known fibrils was consistent with measured properties.