Schmitz Rebecca, Müller Niels, Ullmann Svenja, Vogel Michael
Institut für Festkörperphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
J Chem Phys. 2016 Sep 14;145(10):104703. doi: 10.1063/1.4962240.
We perform molecular dynamics simulations to investigate structural and dynamical properties of ethylene glycol-water (EG-WA) mixtures in mesoporous silica. To obtain comprehensive insights into the dependence of liquid behaviors on the confinement features, we exploit that straightforward modification of the force field parameters allows us to vary the properties of the hydrogen-bond network of the confined liquid, we alter the polarity of the silica surface, and we consider amorphous as well as crystalline matrices. It is observed that the confinement induces a micro-phase separation in the liquid, which qualitatively depends on the properties of both liquid and matrix so that EG or WA molecules may be preferentially adsorbed at the silica surface. Furthermore, it is found that the confinement strongly affects the liquid dynamics. Largely independent of the polarity and structure of the matrix, structural relaxation is about a factor of 10(4) slower at the pore wall than in the pore center. Moreover, the non-Arrhenius temperature dependence of the bulk mixture turns into an Arrhenius behavior of the confined mixture so that the spatial restriction can slow down or speed up the structural relaxation, depending on temperature.
我们进行分子动力学模拟，以研究介孔二氧化硅中乙二醇 - 水（EG - WA）混合物的结构和动力学性质。为了全面深入了解液体行为对受限特征的依赖性，我们利用力场参数的直接修改来改变受限液体氢键网络的性质，改变二氧化硅表面的极性，并考虑非晶态以及晶态基质。观察到受限作用会在液体中引发微相分离，这在定性上取决于液体和基质的性质，使得EG或WA分子可能优先吸附在二氧化硅表面。此外，发现受限作用强烈影响液体动力学。很大程度上与基质的极性和结构无关，在孔壁处的结构弛豫比在孔中心慢约10⁴倍。此外，本体混合物的非阿仑尼乌斯温度依赖性转变为受限混合物的阿仑尼乌斯行为，因此空间限制可以根据温度减缓或加速结构弛豫。
