Structural and Dynamical Properties of Liquids in Confinements: A Review of Molecular Dynamics Simulation Studies

Abstract

Molecular dynamics (MD) simulations are a powerful tool for detailed studies of altered properties of liquids in confinement, in particular, of changed structures and dynamics. They allow, on one hand, for perfect control and systematic variation of the geometries and interactions inherent in confinement situations and, on the other hand, for type-selective and position-resolved analyses of a huge variety of structural and dynamical parameters. Here, we review MD simulation studies on various types of liquids and confinements. The main focus is confined aqueous systems, but also ionic liquids and polymer and silica melts are discussed. Results for confinements featuring different interactions, sizes, shapes, and rigidity will be presented. Special attention will be given to situations in which the confined liquid and the confining matrix consist of the same type of particles and, hence, disparate liquid–matrix interactions are absent. Findings for the magnitude and the range of wall effects on molecular positions and orientations and on molecular dynamics, including vibrational motion and structural relaxation, are reviewed. Moreover, their dependence on the parameters of the confinement and their relevance to theoretical approaches to the glass transition are addressed.

Dynamical Susceptibilities of Confined Water from Room Temperature to the Glass Transition

“…Consistently, molecular dynamics simulations traced such low-frequency broadening to slower water dynamics near the pore walls than in the pore center. 65 The slope of the high-frequency flank, −α HN β HN , amounts to −0.34 for H 2 O and −0.40 for D 2 O, which also indicates a somewhat larger broadening than in most bulk supercooled liquids. 62,64 We emphasize that temperature-dependent changes of the low/high frequency slope at lower/higher than the studied temperatures are not excluded.…”

Cell-Size Space Regulates the Behavior of Confined Polymers: From Nano- and Micromaterials Science to Biology

“…17,18 This system has the advantage of obtaining the statistical average D from multiple droplets of a certain R at the same time. However, it is laborious to assess the R dependence because it is necessary to change the microfluidic device design and the flow rate condition to change R. Furthermore, when the relationship between the diffusion coefficient D and droplet radius R is obtained, it is difficult to determine which of the following factors is responsible for the relationship: (i) small volume, (ii) short-range membrane effects that depend on the distance from the membrane surface on the nanoscale, 19 or (iii) long-range membrane effects proportional to the membrane surface area−volume ratio, S/V.…”

Phosphonium Ionic Liquid‐Activated Sulfur Vulcanization: A Way Forward to Reduce Zinc Oxide Levels in Industrial Rubber Formulations

“…Cross‐linking of two‐dimensional macromolecular polymer chains into three‐dimensional network structures is an essential process by which polymer is converted into durable materials for use in various applications [1–19] . ZnO is a global activator for the sulfur vulcanization process which improves the kinetics of the curing process and promotes the short sulfidic cross‐link formation with higher densities [20–27] .…”