Swallen Stephen F, Traynor Katherine, McMahon Robert J, Ediger M D, Mates Thomas E
Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53705, USA.
J Phys Chem B. 2009 Apr 9;113(14):4600-8. doi: 10.1021/jp808912e.
We have measured self-diffusion coefficients for deeply supercooled tris-naphthylbenzene using secondary ion mass spectrometry. Isotopically labeled multilayer films were prepared by vapor deposition. For samples deposited within a few K of T(g), the evolution of the concentration profile was observed to be Fickian on all accessible length and time scales. Diffusion is enhanced by a factor of approximately 100 at 338 K when compared to the prediction of the Stokes-Einstein model. In combination with previous neutron reflectivity experiments, these measurements quantify the length scale at which dynamics cross over to non-Fickian behavior in supercooled TNB. Comparisons are made between this diffusion data and other measurements of dynamics in supercooled TNB, including probe diffusion and crystal growth rates. An earlier report of self-diffusion coefficients for TNB was in error because the samples were prepared by vapor deposition at T(g) - 50 K, creating very stable glasses in which the concentration profile does not evolve by Fickian diffusion.
我们使用二次离子质谱法测量了深度过冷的三萘基苯的自扩散系数。通过气相沉积制备了同位素标记的多层膜。对于在玻璃化转变温度（Tg）以下几K范围内沉积的样品，在所有可及的长度和时间尺度上，浓度分布的演变均符合菲克定律。与斯托克斯-爱因斯坦模型的预测相比，在338K时扩散增强了约100倍。结合先前的中子反射率实验，这些测量量化了过冷三萘基苯中动力学转变为非菲克行为的长度尺度。将该扩散数据与过冷三萘基苯中其他动力学测量结果进行了比较，包括探针扩散和晶体生长速率。先前关于三萘基苯自扩散系数的报告有误，因为样品是在Tg - 50K下通过气相沉积制备的，形成了非常稳定的玻璃态，其中浓度分布不会通过菲克扩散演变。
