Horstmann R, P Sanjon E, Drossel B, Vogel M
Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany.
J Chem Phys. 2019 Jun 7;150(21):214704. doi: 10.1063/1.5095198.
We use molecular dynamics simulations to ascertain the effects of geometrical restriction on glass-forming tetrahedral liquids. Striving for a broad approach, we study families of waterlike and silicalike liquids, for which we systematically scale the partial charges and, hence, the relevance of the tetrahedral networks. The confined liquids and the confining matrices consist of the same type of particles to avoid disruptive interactions and distorted structures at the interfaces. Spatially resolved analyses show that these neutral confinements still impose static mobility gradients and density correlations on the liquids. We quantify the increasing degree and range of the altered properties upon cooling. For both families of models, common relations describe the confinement effects of all systems with tetrahedral order, while deviations occur for systems with lower polarities and different structures. The observations are rationalized by considering the fact that a pinned wall imprints a static energy landscape to a neighboring liquid. We explore the properties of this landscape based on changes in vibrational motion and structural relaxation and find that typical barrier heights amount to two to three times the activation energy of bulk dynamics. Combining the present and previous results, we predict the evolution of confinement effects down to the glass transition temperature for liquids without fragile-to-strong crossover. In addition, it is found for silicalike liquids that the temperature dependence of dynamic and static correlation lengths from confinement studies is not affected when cooling through fragile-to-strong transitions of the bulk materials, casting doubt on the relevance of these length scales for the glassy slowdown.
我们使用分子动力学模拟来确定几何限制对形成玻璃的四面体液体的影响。为了采用广泛的方法，我们研究了类水和类硅液体家族，为此我们系统地缩放部分电荷，从而确定四面体网络的相关性。受限液体和限制基质由相同类型的粒子组成，以避免界面处的破坏性相互作用和结构扭曲。空间分辨分析表明，这些中性限制仍然会在液体上施加静态迁移率梯度和密度相关性。我们量化了冷却时性质改变的程度和范围。对于这两个模型家族，通用关系描述了所有具有四面体有序的系统的限制效应，而极性较低和结构不同的系统则会出现偏差。通过考虑固定壁会给相邻液体留下静态能量景观这一事实，这些观察结果得到了合理的解释。我们基于振动运动和结构弛豫的变化探索了这种景观的性质，发现典型的势垒高度相当于体相动力学活化能的两到三倍。结合当前和先前的结果，我们预测了对于没有从脆性到强转变的液体，限制效应直至玻璃化转变温度的演变。此外，对于类硅液体，发现当体相材料通过脆性到强转变进行冷却时，限制研究中动态和静态相关长度的温度依赖性不受影响，这对这些长度尺度与玻璃态减速的相关性提出了质疑。
