Magnetohydrodynamic effects in nematic liquid crystals

Abstract

The behaviour of a nematic liquid crystal when it is spun about an axis orthogonal to a magnetic field is predicted to be controlled by the critical angular velocity, ω_c. For spinning speeds below ω_c theory shows that the director makes an increasing angle with the field until at ω_c this angle is 45°. Above ω_c the director should rotate with an angular velocity slightly less than that of the sample. Observation in both regimes allows ω_c to be determined; since it depends on the ratio of the diamagnetic anisotropy to the rotational viscosity coefficient of the nematic, this ratio can be measured. However, an experimental investigation by Eastman et al. [1], suggests that the theoretical relationship between ω_c and this ratio may be in error by a factor of about four. We have reanalysed their data in an attempt to check this important claim and have found that there is in fact good agreement between theory and experiment.