Molecular Dynamics Study of the Structure and Dynamics of Water in Cylindrical Pores

Abstract

The structure and dynamics of confined water in cylindrical pores have been investigated by molecular dynamics simulations. Both rigid (TIP4P) and flexible (BJH) models have been used. Pore radii between 4.2 and 20 Å have been studied; the pore walls are modeled either as a smooth (10−4) Lennard-Jones wall or as a structured wall consisting of (12−6) Lennard-Jones particles. Polar functional groups on the pore surface are modeled by arrays of point charges. We present results on density and orientational distribution functions and on the water mobility. We observe that water transport through nonpolar pores is fast and dominated by the surface layer, whereas transport in polar pores is slowed down relative to bulk liquid water and occurs preferentially through the center of the pore.

A molecular dynamics study of structural transitions in small water clusters in the presence of an external electric field

“…For this purpose the TIP4P 32 potential model has been employed, which has been found to adequately describe many liquid water and ice properties not only at ambient conditions but also in confinement, 26,27 at increased pressure, 1,[3][4][5] at supercooled, 11,33 or supercritical conditions. 34,35 The TIP4P model is adequate for the description of small cluster properties as well, 36,37 and is more susceptible to nucleation than the SPC/E potential.…”

“…A more hydrogenbonded network structure slows reactions due to its increased viscosity, reduced diffusivity, and the less active participation of water molecules. The application of external load ͑pressure͒, [1][2][3][4][5][6][7][8][9] of electric field, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] of ultrasound flow, 25 or the confinement of water thin films between plates or within cylindrical pores 26,27 results in the break-up of the hydrogenbonding network and under certain conditions, the induction of a phase transition between different water forms. These effects remain largely unexplored despite the significance this knowledge has for understanding the solvation behavior and properties of water in biological systems.…”

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles

“…Water mobility trends are also opposite for the two different classes of interface. Translational mobility is enhanced near hydrophobic interfaces 27,89,91 and greatly reduced in the first several solvation shells of hydrophilic ones. 27,32,89,96 In our simulations, rotational mobility is not significantly affected by the hydrophobic interface but is sharply reduced in the regions near the surfactant headgroups.…”

“…Translational mobility is enhanced near hydrophobic interfaces 27,89,91 and greatly reduced in the first several solvation shells of hydrophilic ones. 27,32,89,96 In our simulations, rotational mobility is not significantly affected by the hydrophobic interface but is sharply reduced in the regions near the surfactant headgroups. Similar reductions in the rotational mobilities of water have been observed in simulations of reverse micelles, 32 surfactant monolayers, 97 and the protein-water interface.…”

“…As we saw in the results for the hydrophobic cavity, the water density profiles near weakly interacting interfaces show little structure. 26,27,89,[91][92][93] The density profiles for water near many different types of strongly interacting interfaces show pronounced peaks and valleys indicative of ordered layer formation. 27,28,30,35,89,94 The effect of the water-wall interaction strength has been examined by Hartnig et al, 89 who showed that layering could be induced simply by increasing the interaction strength while holding the form of the potential constant.…”