School of Chemistry, University of Sydney, Sydney N.S.W. 2006, Australia.
J Chem Phys. 2012 Jul 7;137(1):014506. doi: 10.1063/1.4730912.
The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature T(η) is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. T(η) is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity.
剪切应力波动在粘性液体中的持续存在是局部势能最小点的非零剪切应力的直接结果，这种非零剪切应力将应力松弛与固有结构之间的转变联系起来。在二维和三维玻璃形成混合物的模拟中，我们计算了这种固有剪切应力的分布，并证明其方差与温度无关，并且在密度上遵循幂律关系。固有应力仅涉及长波长波动，这表明静态边界条件在确定势能最小化后残留应力方面起着核心作用。定义一个温度 T(η)来描述从高温下由二元碰撞控制的应力松弛到由固有应力松弛主导的低温松弛的转变。发现 T(η)与扩散和粘度的 Stokes-Einstein 标度律的破坏相吻合。
