Photon transmission technique for studying multiple phase transitions in aliquid crystal

A photon transmission technique was used to monitor the multiple phase tran sitions in a 4-butoxyphenyl-4'-declyoxybenzoate benzoate (BOPDOB) liquid cr ystal. Drastic decreases in the transmitted photon intensity (I) were attri buted to the sequential phase transitions in BOPDOB upon cooling, In this p aper, it is assumed that the order parameter rho is proportional to the tra nsmitted photon intensity. The isotropic-nematic and nematic-smectic-A tran sitions were observed and found to be of first order. It was observed that the smectic-A-smectic-C and smectic-C-smectic-G transitions are second orde r. It was found that for the smectic-A-smectic-C transition, critical expon ent crosses over from beta = 0.513 +/- 0.006, which is consistent with mean -held theory, to beta = 0.35 +/- 0.009, which is consistent with heliumlike behavior, as the Ginzburg criterion predicts. The critical exponent for th e smectic-C-smectic-G transition was found to be beta = 0.703 +/- 0.001. Tr ansition temperatures were established at each phase transitions and found to be 84.92 degrees C:, 73.85 degrees C, 52.96 degrees C, and 33.03 degrees C for isotropic-nematic, nematic-smectic-A, smectic-A-smectic-C and. smect ic-C-smectic-G transitions. respectively.