Theory of the spatial transfer of interface-nucleated changes of dynamical constraints and its consequences in glass-forming films.
Theory of the spatial transfer of interface-nucleated changes of dynamical constraints and its consequences in glass-forming films.
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动态约束的界面成核变化的空间转移理论及其在玻璃形成膜中的后果。
DOI：
10.1063/1.5079250
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
K. Schweizer
中科院分区：
文献类型：
--
作者：
A. D. Phan;K. Schweizer
我们制定了一种新理论，说明如何在非线性朗之万方程（NLE）理论方法的动态自由能概念的背景下修改表面或界面处的玻璃形成液体中的笼蔽约束，然后以逐层自举的方式在空间上转移到薄膜内部。任何平均位置（笼中心）的动态自由能涉及来自约束力不同的两个相邻层的贡献。在该理论的最基本层面上，动态自由能的笼蔽分量基本上随距界面的距离呈指数变化，在薄膜中足够深的饱和，相关长度适中，对热力学状态的敏感性较弱。这赋予了计算动力学量梯度所需的动态自由能的所有关键特征的大致指数空间变化，包括定位长度、跳跃距离、笼势垒、集体弹性势垒和α弛豫时间。空间梯度完全是动态的，而不是结构或热力学的起源。该理论适用于硬球流体和不同的界面，这些界面可以是蒸气、粗糙的钉扎颗粒固体、振动（软化）钉扎颗粒固体或光滑的硬壁。它们在空间异质动态自由能层面上的基本描述是相同的，关键的区别来自于第一层，其中动态约束可以根据特定的界面而减弱、软化或几乎不改变。数值计算建立了五个不同模型界面的关键动力学特性梯度的空间依赖性和流体体积分数敏感性。将动态定位长度和玻璃模量的理论预测与具有蒸气界面的系统的模拟和实验进行比较，结果显示出良好的一致性。目前的进展为使用弹性集体 NLE 理论对具有不同界面和化学组成的模型和实验（胶体、分子和聚合物）系统的 α 弛豫时间梯度、解耦现象、Tg 梯度以及许多薄膜平均特性进行定量预测奠定了基础。
We formulate a new theory for how caging constraints in glass-forming liquids at a surface or interface are modified and then spatially transferred, in a layer-by-layer bootstrapped manner, into the film interior in the context of the dynamic free energy concept of the Nonlinear Langevin Equation (NLE) theory approach. The dynamic free energy at any mean location (cage center) involves contributions from two adjacent layers where confining forces are not the same. At the most fundamental level of the theory, the caging component of the dynamic free energy varies essentially exponentially with distance from the interface, saturating deep enough into the film with a correlation length of modest size and weak sensitivity to the thermodynamic state. This imparts a roughly exponential spatial variation of all the key features of the dynamic free energy required to compute gradients of dynamical quantities including the localization length, jump distance, cage barrier, collective elastic barrier, and alpha relaxation time. The spatial gradients are entirely of dynamical, not structural or thermodynamic, origin. The theory is implemented for the hard sphere fluid and diverse interfaces which can be a vapor, a rough pinned particle solid, a vibrating (softened) pinned particle solid, or a smooth hard wall. Their basic description at the level of the spatially heterogeneous dynamic free energy is identical, with the crucial difference arising from the first layer where dynamical constraints can be weakened, softened, or hardly changed depending on the specific interface. Numerical calculations establish the spatial dependence and fluid volume fraction sensitivity of the key dynamical property gradients for five different model interfaces. A comparison of the theoretical predictions for the dynamic localization length and glassy modulus with simulations and experiments for systems with a vapor interface reveals good agreement. The present advance sets the stage for using the Elastically Collective NLE theory to make quantitative predictions for the alpha relaxation time gradient, decoupling phenomena, Tg gradient, and many film-averaged properties of both model and experimental (colloids, molecules, and polymers) systems with diverse interfaces and chemical makeup.
过冷液体中的静态和动态长度尺度：水和环氧丙烷分子动力学模拟的见解
DOI：
10.1063/1.4870089
发表时间：
2014
期刊：
The Journal of chemical physics
影响因子：
--
作者：
F. Klameth;P. Henritzi;M. Vogel
通讯作者：
M. Vogel