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The viscoelastic properties of nematic monodomains containing liquid crystal polymers

Gu, Dongfeng
http://rave.ohiolink.edu/etdc/view?acc_num=case1057759399

Abstract Details

1994, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
The work presented here investigates the viscoelastic properties of nematic materials containing liquid crystal polymers (LCP). We focus on how the elastic constants and the viscosity coefficients of the mixture systems are influenced by polymer architectures. In dynamic light scattering studies of the relaxation of the director orientation fluctuations for the splay, twist, and bend deformation modes, decrease of the relaxation rates was observed when LCPs were dissolved into low molar mass nematics (LMMN). For the side-chain LCPs, the slowing down in the bend mode is comparable to or larger than those of the splay and twist modes. For main-chain LCPs, the relative changes in the relaxation rates for the twist and splay modes are about one order of magnitude larger than that for the bend mode. The results of light scattering under an electric field show that the decrease in the twist relaxation rate is due to a large increase in the twist viscosity and a minor decrease in the twist elastic constant. These changes were found to increase with decrease of the spacer length, with increase of molecular weight, and with decrease of the backbone flexibility. In Freedericksz transition measurements, the splay and bend elastic constants and the dielectric anisotropies of the nematic mixtures were determin ed and the values are 5∼15% lower than those of the pure solvent. From the analysis of the results of Freedericksz transition and light scattering experiments, a complete set of the elastic constants and viscosity coefficients corresponding to the three director deformation modes were obtained for the LCP mixtures. The changes in the viscosity coefficients due to addition of LCPs were analysed to estimate the anisotropic shapes of the polymer backbone via a hydrodynamic model. The results suggest that an oblate backbone configuration is maintained by the side-chain LCPs and a prolate chain configuration appears for the main-chain LCPs. The rheological behavior of a side-chain and a main-chain LCP nematic solutions were investigated. The addition of the side-chain LCP into a flow-aligning LMMN (5CB) induces director tumbling in the mixture, and, the dissolution of the main-chain LCP into a director tumbling LMMN (8CB) makes the solution become a flow-aligning nematic. Based on the hydrodynamic theory, these observations are further confirmation of the chain anisotropies of the LCPs investigated. Ericksen's transversely isotropic fluid model was used to extract the various viscosity coefficients with good accuracy. In addition, we believe that this is the first time the bulk rheological consequences of director tumbling in LMMNs has been observed.
Alex Jamieson (Advisor)
252 p.
viscoelastic properties; nematic monodomains; liquid crystal polymers

Recommended Citations

Citations

  • Gu, D. (1994). The viscoelastic properties of nematic monodomains containing liquid crystal polymers [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1057759399

    APA Style (7th edition)

  • Gu, Dongfeng. The viscoelastic properties of nematic monodomains containing liquid crystal polymers. 1994. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1057759399.

    MLA Style (8th edition)

  • Gu, Dongfeng. "The viscoelastic properties of nematic monodomains containing liquid crystal polymers." Doctoral dissertation, Case Western Reserve University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1057759399

    Chicago Manual of Style (17th edition)

case1057759399
544
© 1994, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.