Determination of the rotational viscosity from the director pattern relaxation in twisted nematic cells

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Abstract
The rotational viscosity γ1 is an essential physical quantity directly related to the response times of liquid crystals. We have developed a new method to determine γ1 which utilizes the capacitive detection of the director pattern relaxation in a twisted nematic cell upon switching off the applied voltage of the twisted nematic liquid-crystal display. Measurements have been performed on two liquid-crystal mixtures. The agreement between the results obtained with the new method and those obtained from a magnetic field-induced nematic deformation method is quite satisfactory.