Photon transmission technique for studying multiple phase transitions in a liquid crystal

A photon transmission technique was used to monitor the multiple phase transitions in a [Formula Presented]-declyoxybenzoate (BOPDOB) liquid crystal. Drastic decreases in the transmitted photon intensity (I) were attributed to the sequential phase transitions in BOPDOB upon cooling. In this paper, it is assumed that the order parameter [Formula Presented] is proportional to the transmitted photon intensity. The isotropic-nematic and nematic–[Formula Presented] transitions were observed and found to be of first order. It was observed that the [Formula Presented]–[Formula Presented] and [Formula Presented]–[Formula Presented] transitions are second order. It was found that for the [Formula Presented]–[Formula Presented] transition, critical exponent crosses over from [Formula Presented] which is consistent with mean-field theory, to [Formula Presented] which is consistent with heliumlike behavior, as the Ginzburg criterion predicts. The critical exponent for the [Formula Presented]–[Formula Presented] transition was found to be [Formula Presented] Transition temperatures were established at each phase transitions and found to be [Formula Presented] [Formula Presented] [Formula Presented] and [Formula Presented] for isotropic-nematic, nematic–[Formula Presented] [Formula Presented]–[Formula Presented] and, [Formula Presented]–[Formula Presented] transitions, respectively.