Viscosity of a liquid crystal near the nematic-smectic A phase transition

We report the results of an x-ray scattering study where both the dynamic and the static properties of a liquid crystal (8OCB) near the nematic-smectic A phase transition were probed. The static, time-averaged data show the gradual formation of smectic layers in the nematic phase, and we find that the smectic order correlation length parallel to the molecular axis diverges with the critical exponent νp=0.70(4) at the transition. The literature value is νb=0.58 for the perpendicular direction. By x-ray photon correlation spectroscopy, we find that the viscosity coefficient η3 shows critical, diverging behavior at the phase transition with a critical exponent x=0.95(5). This contradicts previous light scattering work (x=0.50), but is in good agreement with the theoretical prediction x=3νp-2νb by Hossain et al. [Phys. Rev. B 19, 432 (1979)]