Molecular dynamics study of water between conducting plates

Masakatsu Watanabe, University of Pennsylvania

Abstract

Molecular dynamics simulation has been used to study effects of an external DC electric field, temperature, and density on liquid water between two conducting plates. At an elevated density, anisotropic structures of water layers between conducting plates and the existence of continuous phase transitions were observed: one transition occurs at a critical field, $E\sb0,$ at which long range dipole ordering parallel to the field sets in, the other may be connected with a zero field spontaneous polarization parallel to plates (symmetry breaking transition). Neither transitions may be observed in bulk water. Both phase transitions occur at entropy extrema as a function of the external field, consistent with a previous experimental observation. Dynamical properties, such as diffusion constant, reorientation time, autocorrelation functions, show unique characters, very different from those of bulk water, and confirm the existence of high order (continuous) phase transitions. There are two distinct type of order parameters for this system. One is related to the dipole moment parallel to plates, and another is related to the dipole moment perpendicular to plates. Using these order parameters, a simple Ginzburg-Landau type functional analysis confirms the high order phase transition at $E\sb0$ and symmetry breaking transition at a zero field. In addition, these phase transitions depends on temperature and density of the system. If density decreases or temperature goes high, the field induced phase transition will occur at a very low electric field and the zero-field spontaneous polarization will disappear. These results suggest that two phase transitions are strongly related.

Subject Area

Chemistry|Molecules|Materials science

Recommended Citation

Watanabe, Masakatsu, "Molecular dynamics study of water between conducting plates" (1991). Dissertations available from ProQuest. AAI9212022.
https://repository.upenn.edu/dissertations/AAI9212022

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