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

Abstract

ABSTRACT: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.

Recent Advances in the Rheology of Thermotropic Liquid Crystal Polymers

“…The relaxation spectra, in Fig. 4.8 shows good agreement with the published studies (Yu et al 2007). Equation (4.7) was used for transforming spectrum data into MWD.…”

“…It was considered that in descending frequency sweep and at the low frequency region moduli reached plateau. Yu et al (2007) studied dynamic rheology of thermotropic liquid crystal polymers and also obtained plateau values for the moduli in the low frequency region (Yu et al 2007). No specific details were mentioned regarding the reason of reaching plateau values.…”

“…The existence of solid and liquid phases in the melting process of LCPs, makes the relaxation behaviour of LCPs extraordinary (Gao et al 1996). Three kinds of relaxation mechanisms are available for LCPs: the relaxation of chain orientation, the relaxation of deformed polydomains, and the coalescence of polydomains (or the relaxation of textures) (Yu et al 2007). A small shear strain i.e.…”

“…In addition, the presence of branches and defects is also dominant in the relaxation process of LCPs. In general, there are three kinds of relaxation mechanisms for nematic LCP: the relaxation of chain orientation, the relaxation of deformed polydomains, and the coalescence of polydomains (or the relaxation of textures) (Yu et al 2007). The relaxation of chain orientation without constraint is a much faster process (Wiberg et al 1998).…”

Dynamic mechanical and thermal behavior of novel liquid-crystalline polybutadiene-diols with azobenzene groups in side chains

“…As presented by Yu et al (2007), the temperature regions for transitions in the material can be also detected from the much sensitive tan d vs. T plot. When cooling samples MA 0.2-0.6 from an isotropic state, a nematic mesophase is formed.…”