Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA.
J Chem Phys. 2013 Mar 28;138(12):12A534. doi: 10.1063/1.4790399.
Activated transport in liquids--supercooled liquids in particular--occurs via mutual nucleation of alternative, aperiodic minima of the free energy. Xia and Wolynes [Proc. Natl. Acad. Sci. U.S.A. 97, 2990 (2000)] have made a general argument that at temperatures near the ideal glass transition, the surface penalty for this kind of nucleation is largely determined by the temperature and the logarithm of the size of the vibrational fluctuation of rigid molecular units about the local minimum. Here, we independently show how to estimate this surface tension and, hence, the activation barrier for the activated transport for several actual liquids, using their structure factors and knowledge of the finite-frequency elastic constants. In this estimate, the activation free energy, while depending on the configurational entropy, also depends on the elastic modulus as in the "shoving" models. The resulting estimates are however consistent with the estimate provided by Xia and Wolynes' argument near the glass transition and, in addition, reflect the barrier softening effects predicted earlier for fragile substances.
液体中的活化传输——特别是过冷液体——通过自由能的交替非周期性极小值的相互成核来实现。Xia 和 Wolynes [Proc. Natl. Acad. Sci. U.S.A. 97, 2990 (2000)]提出了一个普遍观点，即在接近理想玻璃转变温度的温度下，这种成核的表面惩罚主要由温度和刚性分子单元关于局部极小值的振动波动的大小的对数决定。在这里，我们独立地展示了如何使用它们的结构因子和有限频率弹性常数的知识来估计这种表面张力，从而估计几种实际液体的活化输运的激活能垒。在这个估计中，激活自由能虽然取决于构象熵，但也像“推挤”模型一样取决于弹性模量。然而，得到的估计与 Xia 和 Wolynes 在玻璃转变附近的论点提供的估计是一致的，此外，还反映了先前对脆弱物质预测的势垒软化效应。
