Science and Technology Division, Corning Incorporated, Corning, New York 14831, USA.
J Chem Phys. 2011 Dec 7;135(21):214502. doi: 10.1063/1.3664744.
The physical origin of stretched exponential relaxation is considered by many as one of the oldest unsolved problems in science. The functional form for stretched exponential relaxation can be deduced from the axiomatic diffusion-trap model of Phillips. The model predicts a topological origin for the dimensionless stretching exponent, with two "magic" values emerging: β = 3/5 arising from short-range molecular relaxation pathways and β = 3/7 for relaxation dominated by longer-range interactions. In this paper, we report experimental confirmation of these values using microscopically homogeneous silicate glass specimens. Our results reveal a bifurcation of the stretching exponent, with β = 3/5 for stress relaxation and β = 3/7 for structural relaxation, both on macroscopic length scales. These results point to two fundamentally different mechanisms governing stress relaxation versus structural relaxation, corresponding to different effective dimensionalities in configuration space during the relaxation process.
拉伸指数弛豫的物理起源被许多人认为是科学中最古老的未解问题之一。拉伸指数弛豫的函数形式可以从菲利普斯的扩散-陷阱模型的公理推导出来。该模型预测了无维拉伸指数的拓扑起源，出现了两个“神奇”的值：β=3/5 来自短程分子弛豫途径，β=3/7 来自由长程相互作用主导的弛豫。在本文中，我们使用微观均匀的硅酸盐玻璃样品报告了对这些值的实验证实。我们的结果揭示了拉伸指数的分岔，在宏观长度尺度上，应力弛豫的β=3/5，结构弛豫的β=3/7。这些结果表明，两种基本不同的机制控制着应力弛豫与结构弛豫，这对应于弛豫过程中构型空间中的不同有效维度。
