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Describes a new method for obtaining accurate critical shear rates at which homogeneous and roll instabilities may occur in thin samples of nematic liquid crystal subjected to simple shear flow. The particular arrangement considered is that in which the anisotropic axis of the liquid crystal is initially uniformly aligned parallel to the bounding plates and perpendicular to the direction of the flow. Exact expressions for determining the threshold values for all nematic materials are first obtained. The authors illustrate how one employs the technique developed by obtaining accurate values for the material MBBA.

This paper presents a new method for determining the critical threshold values at which both homogeneous and roll-type instabilities may appear when thin layers of nematic liquid crystal are subjected to Couette flow. The anisotropic axis of the material is initially uniformly aligned parallel to the axial direction and the effect of a stabilising, axially oriented, uniform magnetic field is allowed for in calculations. Carrying out a linear stability analysis of the continuum equations, we employ a Fourier series method to derive an expression for determining the critical shear rate at which instability occurs. Thresholds for both homogeneous and roll instabilities are obtained and their variation with rotation rate and applied magnetic field strength is examined for the material MBBA.

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