Twist Viscosity of a Side-Chain Liquid-Crystalline Polysiloxane Dissolved in a Tumbling Nematic Solvent
2000; American Chemical Society; Volume: 33; Issue: 5 Linguagem: Inglês
10.1021/ma991666k
ISSN1520-5835
AutoresPei-Yuan Liu, Alex M. Jamieson, Ning Yao,
Tópico(s)Material Dynamics and Properties
ResumoThe dynamics of the twist distortion was characterized by electric-field-dependent dynamic light scattering (EFDLS) for a dilute solution of a side-chain liquid crystalline polysiloxane (SCLCP) dissolved in the tumbling nematic solvent, 4'-octyl-4-cyanobiphenyl (8CB). The results show a decrease in twist relaxation rate on dissolution of the SCLCP due to a large increase in twist viscosity δγ1 with negligible change in twist elastic constant K22. By comparing the twist viscosity values, γ1 = α3 − α2, with previous measurements of the strain periodicity of oscillations in the shear stress transients due to director tumbling, γp = (π/δp)(1 + δp2), where δp = (−α3/α2)1/2, we further investigate the corresponding changes in Leslie viscosities, δα2 and δα3. The results indicate that δα2 and δα3 have opposite signs. These observations, together with literature data on the electrorheological behavior of these solutions, can be self-consistently described by a hydrodynamic model of the viscous dissipation by Brochard, modified through inclusion of an additional dissipation process which derives from an elastic torque between director rotation and LCP orientation.
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