Saw Shibu, Dasgupta Chandan
Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2016 Aug 7;145(5):054707. doi: 10.1063/1.4959942.
Confinement by walls usually produces a strong modulation in the density of dense liquids near the walls. Using molecular dynamics simulations, we examine the effects of the density modulation on the spatially resolved dynamics of a liquid confined between two parallel walls, using a resolution of a fraction of the interparticle distance in the liquid. The local dynamics is quantified by the relaxation time associated with the temporal autocorrelation function of the local density. We find that this local relaxation time varies in phase with the density modulation. The amplitude of the spatial modulation of the relaxation time can be quite large, depending on the characteristics of the wall and thermodynamic parameters of the liquid. To disentangle the effects of confinement and density modulation on the spatially resolved dynamics, we compare the dynamics of a confined liquid with that of an unconfined one in which a similar density modulation is induced by an external potential. We find several differences indicating that density modulation alone cannot account for all the features seen in the spatially resolved dynamics of confined liquids. We also examine how the dynamics near a wall depends on the separation between the two walls and show that the features seen in our simulations persist in the limit of large wall separation.
壁面限制通常会在壁面附近的稠密液体密度中产生强烈调制。我们使用分子动力学模拟，以液体中粒子间距离的一小部分为分辨率，研究了密度调制对限制在两个平行壁面之间的液体的空间分辨动力学的影响。局部动力学通过与局部密度的时间自相关函数相关的弛豫时间来量化。我们发现这种局部弛豫时间与密度调制同相变化。弛豫时间的空间调制幅度可能相当大，这取决于壁面的特性和液体的热力学参数。为了区分限制和密度调制对空间分辨动力学的影响，我们将受限液体的动力学与不受限液体的动力学进行了比较，在不受限液体中，通过外部势诱导出类似的密度调制。我们发现了几个差异，表明仅密度调制不能解释在受限液体的空间分辨动力学中看到的所有特征。我们还研究了壁面附近的动力学如何依赖于两个壁面之间的间距，并表明我们模拟中看到的特征在大壁间距的极限情况下仍然存在。
