Electric-Field Induced Restructuring of Water at a Platinum-Water Interface: A Molecular Dynamics Computer Simulation

Understanding the inherent response of water to an external electric ͑E͒-field is useful towards decoupling the role of E-field and surface in several practically encountered situations, such as that near an ion, near a charged surface, or within a biological nanopore. While this problem has been studied in some detail through simulations in the past, it has not been very amenable for theoretical analysis owing to the complexities presented by the hydrogen ͑H͒ bond interactions in water. It is also difficult to perform experiments with water in externally imposed, high E-fields owing to dielectric breakdown problems; it is hence all the more important that theoretical progress in this area complements the progress achieved through simulations. In an attempt to fill this lacuna, we develop a theory based on relatively simple concepts of reaction equilibria and Boltzmann distribution. The results are discussed in three parts: one pertaining to a comparison of the key features of the theory vis a vis published simulation/experimental results; second pertaining to insights into the H-bond stoichiometry and molecular orientations at different field strengths and temperatures; and the third relating to a surprising but explainable finding that H-bonds can stabilize molecules whose dipoles are oriented perpendicular to the direction of field ͑in addition to the E-field and H-bonds both stabilizing molecules with dipoles aligned in the direction of the field͒.

Section: Introductionmentioning

confidence: 99%

Influence of electric field on the hydrogen bond network of water

Suresh

Satish

Choudhary

2006

“…18 under certain charge densities. With field increase, the crystallization of a larger domain, but not of all of the confined water, towards a strained cubic ice-I has been facilitated.…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Vegiri

Schevkunov

2001

The present work constitutes a thorough study of the response of a relatively small water cluster (Nϭ32) to external static electric fields in the 0.5ϫ10 7 to 10 8 V/cm range, at Tϭ200 K. As the electric field is varied, the system undergoes a phase transition to structures resembling incomplete nanotubes consisting of stacked squares arranged perpendicularly to the field direction. For further field increase the system transforms continuously to more open structures, reminiscent of the proton ordered forms of cubic ice, found also in the liquid. Regarding the dynamic response of the cluster, this is reflected in a profound way on the nonmonotonic variation of the reorientational decay rates of the molecular intrinsic axes and of the self-diffusion coefficients along and perpendicular to the field lines. In general the external field induces a considerable increase of the reorientational decay rates of all axes, except for the strongest field where the electrofreezing effect is observed. Reorientational relaxation has been found to obey a stretched exponential behavior of the Kohlrausch-Williams-Watts-type, where a one-to-one correspondence between the ␤-exponent variation with the field, molecular cooperativity, and translational diffusion has been established.

“…There are many computational studies on confined water, [4][5][6][7][8][9][10][11][12] some of the pioneering works date back to 1980s. 4 One of the earlier computer simulations focusing on liquidsolid phase transitions 13 showed that water between hydrophobic surfaces freezes into a bilayer form of crystalline ice when temperature is lowered under a fixed normal pressure.…”

Section: Introductionmentioning

confidence: 99%

Phase diagram of water between hydrophobic surfaces

Koga

Tanaka²

2005

136

147

Molecular dynamics simulations demonstrate that there are at least two classes of quasi-two-dimensional solid water into which liquid water confined between hydrophobic surfaces freezes spontaneously and whose hydrogen-bond networks are as fully connected as those of bulk ice. One of them is the monolayer ice and the other is the bilayer solid which takes either a crystalline or an amorphous form. Here we present the phase transformations among liquid, bilayer amorphous ͑or crystalline͒ ice, and monolayer ice phases at various thermodynamic conditions, then determine curves of melting, freezing, and solid-solid structural change on the isostress planes where temperature and intersurface distance are variable, and finally we propose a phase diagram of the confined water in the temperature-pressure-distance space.