Madsen Anders, Als-Nielsen Jens, Grübel Gerhard
European Synchrotron Radiation Facility, B.P. 220, F-38045 Grenoble, France.
Phys Rev Lett. 2003 Feb 28;90(8):085701. doi: 10.1103/PhysRevLett.90.085701. Epub 2003 Feb 26.
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 nu( parallel )=0.70(4) at the transition. The literature value is nu( perpendicular )=0.58 for the perpendicular direction. By x-ray photon correlation spectroscopy, we find that the viscosity coefficient eta(3) 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=3nu( parallel )-2nu( perpendicular ) by Hossain et al.
我们报告了一项X射线散射研究的结果，该研究探测了向列相-近晶A相转变附近的液晶（8OCB）的动态和静态特性。静态的、时间平均的数据显示了向列相中近晶层的逐渐形成，并且我们发现在转变处，平行于分子轴的近晶序关联长度以临界指数ν(平行)=0.70(4)发散。文献中垂直方向的数值为ν(垂直)=0.58。通过X射线光子相关光谱法，我们发现粘度系数η(3)在相变处呈现临界发散行为，临界指数χ=0.95(5)。这与之前的光散射研究结果（χ=0.50）相矛盾，但与Hossain等人的理论预测χ=3ν(平行)-2ν(垂直)高度吻合。
