Rotational Viscosity Coefficient Research Articles

Rotational Viscosity of a Smectic-CLiquid-Crystalline Phase

We report measurements of the rotational viscosity coefficient in the smectic-$C$ and nematic phases of heptyloxyazoxybenzene. The measurements are interpreted in terms of a model of the smectic-$C$ phase in which the molecules reorient about the normal to the smectic layers. Extrapolated to the nematic-smectic transition temperatures, the viscosity in the smectic-$C$ phase is lower by a factor of 0.4 than that in the nematic phase. A reverse pretransition effect is observed in the nematic phase.

Polypeptide liquid crystals: Magnetic susceptibility, twist elastic constant, rotational viscosity coefficient, and poly-γ-benzyl-L-glutamate sidechain conformation

The bulk magnetic susceptibilities of several synthetic polypeptides have been measured. The observed anisotropy of the diamagnetic susceptibility Δχ for oriented nematic liquid crystals of poly-γ-benzyl-L-glutamate (PBLG) in dichloromethane is 7.0±0.7×10−6 emu/mole. For a PBLG axial ratio of 150, a value of the twist elastic constant K22=273×10−7 emu cgs is calculated by measuring the critical magnetic field for untwisting the cholesteric supra molecular structure in the liquid crystal. The rate of reorientation of the nematic director of an aligned nematic PBLG structure yields a value for the rotational viscosity coefficient, γ1=2.8×105 P. K22 and γ1 appear to be sensitive to the polypeptide axial ratio and solvent composition. The possibility of extracting polypeptide sidechain structural information from Δχ measurements in the liquid crystal is discussed.

On Pulsatile Blood Flow

In this paper pulsatile blood flow through rigid circular tubes due to a sinusoidally varying pressure gradient is analyzed using a microcontinuum model of blood. A new boundary condition, which is in accord with experimental observations on blood flow in small rigid tubes, has been proposed to describe red blood cell rotations at a solid boundary. General solutions to the governing equations are obtained through application of consecutive Hankel and Laplace transforms. The steady pulsatile solutions for velocity and cell rotation are also given. The plasma viscosity, rotational viscosity, and rotational gradient coefficients are determined as functions of hematocrit from the experimental in vitro steady blood flow data of Bugliarello and Sevilla. These coefficients are then used to predict their pulsatile velocity profile data. Excellent agreement is obtained when non-Newtonian effects are absent.

Measurements of the Rotational Viscosity Coefficient and the Shear-Alignment Angle in Nematic Liquid Crystals

A method is described for the direct measurement of the shear-alignment angle in a nematic liquid crystal. Results of such measurements are reported for the nematic phases of three compounds: PAA ($p$, ${p}^{\ensuremath{'}}$-azoxydianisole), MBBA ($p$-methoxybenzylidene-${p}^{\ensuremath{'}}\ensuremath{-}n$-butylaniline), and HBAB ($p\ensuremath{-}n$-hexyloxybenzylidene-${p}^{\ensuremath{'}}$-aminobenzonitrile). We also report measurements of the rotational viscosity coefficient for the same compounds. In contrast to a recent report by G\"ahwiller, no orientational instability was found in HBAB.

Transport Equations of Multicomponent Systems of Polyatomic Molecules. II

Expressions for the rotational diffusion coefficient, the rotation viscosity coefficients, and the rotational coefficient of heat conductivity are developed for a multicomponent system of polyatomic molecules. In the present work, the same method used in Paper (I) of this series has been followed to obtain the rotational diffusion, viscosity, and heat conduction coefficients of a multicomponent system of polyatomic molecules.

Flow stability of viscous liquid layer with moment stresses on an inclined plane

The flow stability of a liquid layer on an inclined plane with account for molecular spin [1, 2] has been considered in [3] in the absence of moment stresses within the liquid. It was shown in [3] that molecular spin has a destabilizing effect on the flow. In the following we study the combined effect of molecular spin and internal moment stresses on the behavior of three-dimensional disturbances. The validity of Squire's theorem is established. The flow stability of a layer of relatively long-wave disturbances is studied by the method of sequential approximations [4, 5] under the assumption that the rotational viscosity coefficient ηr is significantly smaller than the Newtonian viscosity coefficient η.