1. Role of confinement in water solidification under electric fields
Guoxi Nie, Yu Wang and Jiping Huang
Department of Physics, Fudan University, Shanghai , China
I. Introduction
III. Result
Investigation to phase transition of water has a fun-damental meaning in physical, chemical and biolo-gical studies, as well as the agricultural, industrial applications. There are some different behaviors bet-ween confined and bulk water. For example, althou-gh the normal freezing temperature for bulk water is 0℃, the forming of monolayer ice at 300K has been reported[1]. Additionally, using electric field can promote solidification too[2,3], because of the rearrangement of water structure through the torque experienced by water molecular dipoles.
Lateral diffusion coefficients for the perpendicular and parallel field systems, from which we can clearly see the shift of critical electric field for both systems.
However, the topic on critical electric field strength is controversial. First, due to the limit of water models and time scale, critical strength of exper- iments is much weaker than that of simulations[4]. Second, in simulation works using perpendicular field, the critical field strengths range from 10 to tens of V/nm.
In this work, we find that confinement can impede electro-freezing, and it is easier to freeze under parallel field. And we explain it with water dipole orientation incorporated with the anisotropic Clausius-Mossotti equation.
IV. Discussion
Average molecular dipole moments along the field direction.
II. Method
Average molecular dipole moments in X, Y and Z directions.
Snapshot of the system. The walls’ distance, d, is increased from 1.2 to 4.4nm (from confined scale to bulk scale). And the field strength ranges from 0 to 50V/nm.
Average no. of H-bonds per water molecule corresponding to different field strengths.
V. Conclusion
Reference
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Confinement at the nano-scale can impede water solidification in case of external electric fields; this result is in contrast to the common knowledge that confinement promotes water solidification. Also, water solidification is easier to occur with a parallel electric field than a perpendicular one. The simulation results have been well understood and generalized by developing the energy theory based on the anisotropic Clausius-Mossotti equation. As revealed by us, the general mechanism originates from the effect of walls’ confinement on the electro-orientations of water molecules.