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arXiv 1901.01094cond-mat.softcond-mat.mtrl-scicond-mat.stat-mech
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玻璃形成膜中界面形核动力学约束变化的空间转移理论及其后果

Theory of the Spatial Transfer of Interface-Nucleated Changes of Dynamical Constraints and Its Consequences in Glass-Forming Films

Anh D. Phan, Kenneth S. Schweizer

摘要:

我们制定了一个新的理论如何在玻璃形成液体的表面或界面的笼约束进行修改,然后在空间上转移,在一个逐层自举的方式,到膜内部的非线性朗之万方程理论方法的动态自由能概念的背景下。在任何平均位置处的动态自由能涉及来自两个相邻层的贡献,其中约束力不相同。在最基本的理论水平上,动态自由能的锁定分量基本上随距离界面呈指数变化,饱和到足够深的膜中,具有适度大小的相关长度和对热力学状态的弱敏感性。这赋予了计算动力学量的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,所述动力学量包括局部化长度、跳跃距离、笼势垒、集体弹性势垒和α弛豫时间。空间梯度完全是动力学的,而不是结构或热力学的。该理论是实现硬球流体和不同的接口,可以是蒸汽,粗糙的钉扎粒子固体,振动钉扎粒子固体,或光滑的硬壁。它们在空间异质动态自由能水平上的基本描述是相同的,关键的区别来自第一层,其中动态约束可以根据特定的界面而被削弱、软化或几乎不改变。数值计算建立了空间依赖性和流体体积分数的敏感性的关键动力学特性梯度为五个不同的模型接口。的动态本地化长度和玻璃态模量的理论预测与模拟和实验系统与蒸汽界面的比较显示出良好的一致性。

英文摘要:

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 theory approach. The dynamic free energy at any mean location 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 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 entire of dynamical, not structural nor 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 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. 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.

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