Rheology and relaxation processes in a melting thermotropic liquid-crystalline polymer

The relaxation behavior of a thermotropic liquid-crystalline polymer (TLCP), LC-5000 from Unichika, Japan, was investigated by rheology and optical microscopy. The solid-nematic transition was shown by DSC and dynamic temperature ramp. The transitions of dynamic modulus with temperature correspond to the end of the melting process. The TLCP is composed of unmelted solid crystals and nematic liquid crystal during the melting process. Macroscopically, it changes from a viscoelastic solid to a viscoelastic liquid in this process, as verified by creep test and dynamic frequency sweep under different temperature. The relaxation spectra of the TLCP under different temperature were calculated from the dynamic modulus. The characteristic relaxation processes determined from the relaxation spectrum are consistent with the observation from polarized optical microscopy. During melting, in particular, the relaxation of deformed polydomains and chain orientation slows down due to the constraining effects of unmelted solid crystals. (c) 2007 Wiley Periodicals, Inc.