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Abstract
The dynamic response of 5CB and 8CB films with a free surface in an external magnetic field was investigated. The magnetic field was initially above the threshold for the Freedericksz transition. Two kinds of time constants were measured optically: one is the turn off time constant when the magnetic field was reduced to a value below the threshold, and the other is the response time with the magnetic field slightly changed but still above the threshold.
The results for samples with various thickness were compared with those films sandwiched between two glass substrates. The differences were analyzed with backflow taken into account. A satisfactory fit with the theory was obtained. Several viscosity coefficients for these two liquid crystal materials have also been determined.