Twist Viscosity of a Side-Chain Liquid-Crystalline Polysiloxane Dissolved in a Tumbling Nematic Solvent

Abstract

The 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 δγ 1 with negligible change in twist elastic constant K22. By comparing the twist viscosity values, γ1 ) R3 -R2, with previous measurements of the strain periodicity of oscillations in the shear stress transients due to director tumbling, γp ) (π/δp)(1 + δp 2 ), where δp ) (-R3/R2) 1/2 , we further investigate the corresponding changes in Leslie viscosities, δR2 and δR3. The results indicate that δR2 and δR3 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.

Alignment of liquid crystals by topographically patterned polymer films prepared by nanoimprint lithography

“…The anchoring energy is 9 ϫ 10 −6 J/m 2 for the linear line pattern with a pitch of 2.5 m. The bend and twist elastic constants used in the calculation are 4.9 ϫ 10 −12 and 2.4ϫ 10 −12 N, respectively. 24 This value is FIG. 3.…”

Rheological Properties and Conformation of a Side-Chain Liquid Crystal Polysiloxane Dissolved in a Nematic Solvent

“…δγ 1 ∼ 0). 30,31 To rationalize these discrepancies, a phenomenological modification of the Brochard hydrodynamic model was proposed by Yao and Jamieson 15 which results in improved agreement with experiment. In particular, the theory enables a self-consistent treatment of ER data, stress transient data, and EFDLS results on solutions of a polysiloxane side-chain LCP in various LMMNs.…”

“…In particular, the theory enables a self-consistent treatment of ER data, stress transient data, and EFDLS results on solutions of a polysiloxane side-chain LCP in various LMMNs. 15,[29][30][31] The modification is based on the assumption that for a LCP/LMMN solution an additional contribution to the hydrodynamic torque can arise from an elastic coupling between the LMMN director and the LCP director. 15 In the present work, we provide a further test of the hydrodynamic theory, using SANS measurements to directly probe the anisotropic radii of gyration R g| and R g⊥ of a side-chain polysiloxane LCP with cyanobiphenyl mesogenic side group dissolved in deuterated 4′-pentyl-4-cyanobiphenyl (5CB).…”

Microstructures Based on Thermotropic Liquid‐Crystalline Polymers in the Low Molar Mass Nematogenic 5CB

“…[11] There is also a tendency of the chain to be aligned with the field of the LMMN defining an anisotropic shape for the polymer. [12] The degree of anisotropy depends on the polymer backbone flexibility, molecular weight, spacer length, and if the polymer exhibits nematic or smectic phases. For the mixtures containing a liquid-crystalline polymer, the average nematic axis is defined by the director n of the LMMN; and although the polymer chains exhibit a distribution of orientations, the mesogenic groups in the polymer tend to orient parallel to the vector director of the liquid crystal solvent.…”

“…For the mixtures containing a liquid-crystalline polymer, the average nematic axis is defined by the director n of the LMMN; and although the polymer chains exhibit a distribution of orientations, the mesogenic groups in the polymer tend to orient parallel to the vector director of the liquid crystal solvent. [12] The aim of this work is to demonstrate the organization of microstructures formed by two different chiral side chain liquidcrystalline polymers (SCLCP), P 11M and P 4M , in 4 0 -n-pentyl-4-cyanobiphenyl (5CB) by means of polarized optical microscopy (POM). The POM technique allows a good understanding of the system, describing the mixtures according to the formed textures from the classic morphologies found in neat liquid crystals.…”