Structure and Dynamics of Acetonitrile Confined in a Silica Nanopore

Abstract

Acetonitrile confined in silica nanopores with surfaces of varying functionality is studied by means of molecular dynamics simulation. The hydrogen-bonding interaction between the surface and the liquid is parametrized by means of first-principles molecular dynamics simulations. It is found that acetonitrile orders into bilayer like structures near the surface, in agreement with prior simulations and experiments. A newly developed method is applied to calculate relevant time correlation functions for molecules in different layers of the pore. This method takes into account the short lifetimes of the molecules in the layers. We compare this method with prior techniques that do not take this lifetime into account and discuss their pitfalls. We show that in agreement with experiment, the dynamics of the system may be described by a two population model that accounts for bulk-like relaxation in the center and frustrated dynamics near the surface of the pore. Specific hydrogen-bonding interactions are found to play a large role in engendering this behavior.

Polarizability Anisotropy Relaxation in Nanoconfinement: Molecular Simulation Study of Acetonitrile in Silica Pores

“…This behavior is characteristic of a liquid confined in a wetting nanopore. 53 It has been observed in previous simulations that acetonitrile molecules adopt a preferential orientation relative to the pore surface 24,25 and that this preference is related to the surface charge distribution. Because of the interface curvature and roughness, these orientational preferences are less clear-cut than in the case of acetonitrile next to a flat crystalline silica surface.…”

“…56 Proximity to an attractive (wetting) surface also restricts the mobility of molecules in the vicinity of the interface, 57,58 including acetonitrile−silica interfaces. 25,31 We examine here how both of these effects manifest themselves in the present systems.…”

“…Similar results for S(t) for acetonitrile in silica pores have been obtained in previous work. 25 We consider the orientational TCF corresponding to the second rank Legendre polynomial of the orientation of the molecular symmetry axis:…”

Molecular dynamics study of oil detachment from an amorphous silica surface in water medium

“…They investigated the adsorption on (1 1 1), (2 2 0) and (3 3 1) surface on silica. Other authors also studied the amorphous silica [23][24][25][26] that is usually obtained by annealing from 8000 to 300 K. Yang's result may help to explain the effect of amorphous silica such as fused quartz on oil detachment.…”

“…In recent years, with the computer power increasing, molecular dynamics (MD) simulation has become a powerful tool to study the structural and properties of surfactant, silica substrates at the microscopic level [23]. It can also provide molecular-scale understanding of oil droplet detachment from solid surfaces, which is difficult to obtain from experiments.…”