Wetting and dewetting of narrow hydrophobic channels by orthogonal electric fields: Structure, free energy, and dynamics for different water models

Abstract

Wetting and dewetting of a (6,6) carbon nanotube in presence of an orthogonal electric field of varying strengths are studied by means of molecular dynamics simulations using seven different models of water. We have looked at filling of the channel, occupancy and structure of water inside it, associated free energy profiles, and also dynamical properties like the time scales of collective dipole flipping and residence dynamics. For the current systems where the entire simulation box is under the electric field, the nanotube is found to undergo electrodrying, i.e., transition from filled to empty states on increase of the electric field. The free energy calculations show that the empty state is the most stable one at higher electric field as it raptures the hydrogen bond environment inside the carbon nanotube by reorienting water molecules to its direction leading to a depletion of water molecules inside the channel. We investigated the collective flipping of water dipoles inside the channel and found that it follows a fast stepwise mechanism. On the dynamical side, the dipole flipping is found to occur at a faster rate with increase of the electric field. Also, the rate of water flow is found to decrease dramatically as the field strength is increased. The residence time of water molecules inside the channel is also found to decrease with increasing electric field. Although the effects of electric field on different water models are found to be qualitatively similar, the quantitative details can be different for different models. In particular, the dynamics of water molecules inside the channel can vary significantly for different water models. However, the general behavior of wetting and dewetting transitions, enhanced dipole flips, and shorter residence times on application of an orthogonal electric field hold true for all water models considered in the current work.

Transport of hydrated nitrate and nitrite ions through graphene nanopores in aqueous medium

“…It is worthwhile to mention that different water models were considered in some of the earlier studies on passage of water through carbon nanotubes in presence of electric fields. [50,69] The SPC/E water model was found to give results which were qualitatively similar to those given by other water models. The permeation of ions and water molecules through nanopores on application of pressure has also been investigated in some recent studies.…”

“…We note that the applied electric field of the current study is similar or lower than the maximum field used in many earlier studies. [24,[44][45][46][47][48][49][50][51] The MD simulations were carried out for equilibration of 10 ns with no electric field and then for another 10 ns under an applied electric field using the GROMACS program. [52] F I G U R E 1 The simulations were carried out with a time step of 2 fs at a constant volume and temperature with Nosé-Hoover thermostat.…”

Orientational and Folding Thermodynamics via Electric Dipole Moment Restraining

“…Notwithstanding, we deliberately carried out these MD simulations in larger systems to avoid as much as possible finite-size effects (see Figure S2 in the Supporting Information); thus, our results should hold for bigger homogeneous systems, but care should be taken when extrapolating to transport phenomena in inhomogeneous systems. Further systematic studies assessing water models, box sizes, long-range electrostatic schemes, and inhomogeneous systems must be carried out to precisely define the threshold for relevant thermodynamics effects of external potentials on water, as done by others. ,− …”

Electric Field Induced Dewetting of Hydrophobic Nanocavities at Ambient Temperature

“…It is also reported that the electric field can induce the evaporation of water confined in-between hydrophobic nanocavities immersed in aqueous solutions [37]. Furthermore, wetting and dewetting of narrow hydrophobic nanocavities induced by electric fields have been studied by Kayal and Chandra [39]. These studies have mainly focused on the system of either end of the nanopores in contact with a liquid water bath.…”