Zhang Yue, Fakhraai Zahra
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
Phys Rev Lett. 2017 Feb 10;118(6):066101. doi: 10.1103/PhysRevLett.118.066101.
Surface diffusion of molecular glasses is found to be orders of magnitude faster than bulk diffusion, with a stronger dependence on the molecular size and intermolecular interactions. In this study, we investigate the effect of variations in bulk dynamics on the surface diffusion of molecular glasses. Using the tobacco mosaic virus as a probe particle, we measure the surface diffusion on glasses of the same composition but with orders of magnitude of variations in bulk relaxation dynamics, produced by physical vapor deposition, physical aging, and liquid quenching. The bulk fictive temperatures of these glasses span over 35 K, indicating 13 to 20 orders of magnitude changes in bulk relaxation times. However, the surface diffusion coefficients on these glasses are measured to be identical at two temperatures below the bulk glass transition temperature T_{g}. These results suggest that surface diffusion has no dependence on the bulk relaxation dynamics when measured below T_{g}.
分子玻璃的表面扩散比体相扩散快几个数量级，且对分子大小和分子间相互作用的依赖性更强。在本研究中，我们研究了体相动力学变化对分子玻璃表面扩散的影响。使用烟草花叶病毒作为探针粒子，我们测量了在相同组成但通过物理气相沉积、物理老化和液体淬火产生的体相弛豫动力学有几个数量级变化的玻璃上的表面扩散。这些玻璃的体相虚构温度跨度超过35 K，表明体相弛豫时间有13到20个数量级的变化。然而，在低于体相玻璃化转变温度Tg的两个温度下，测量到这些玻璃上的表面扩散系数是相同的。这些结果表明，在低于Tg的温度下测量时，表面扩散与体相弛豫动力学无关。
