Electric Field Effect on Water

  • Thread starter Daniel_H_S
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  • #1
I'm trying to calculate the attractive force between two Water Molecules under the effect of an Electric field and I'm completely stumped. Its part of a research project I'm doing at my new work, I'm sure I'm just forgetting a formula for it from somewhere, I'm sure I remember covering this sort of effect at uni. Any help would be greatly appreciated.

Answers and Replies

  • #2
You might try modeling each molecule as a dipole.
  • #3
as manchot said, water molecules can be approximated (to fairly good accuracy) as dipoles.

The electric field will of course exert no net force on a water molecule; so i assume you mean the force between water molecules after they have all been aligned? If so, this will turn into a n-body problem (of sorts)... i think the details of your situation are pretty important.
  • #4
Pure water normally has molecules that contain 1 through 9 or more H2O units. A small electric field does not influence the number of H2O units in a molecule.

Normally, an electric field is used to cause oxidation / reduction reactions of stuff within water, for example: electrolytic coating and galvanic cell processes. Pure water is dielectric material. Ionization energy applies to a single H2O.

Perhaps if you provide more detail as 'attractive force', someone can provide a less nebulous response.
  • #5
It is not a trivial problem. An electric field will polarize the molecules, changing their dipole moment and also orienting it. To find the interaction energy you need to know the polarizability of a water molecule in vacuum (a 3d tensor) and also you need to know the polarization of your electric field. Once you knwo this you will need to asume a geometry for the water molecules and then you can calculate it. a dime of waters (2 water molecules in an optimal configuration) in vacuum has an interaction energy of the order of 250 meV. This is the energy o a hydrogen bond. An electric field polarized in the direction of the Hbond will make this interaction stronger (how much, this depends on the polarizability (alpha) and on the electric field). Polarized perpendicular to the Hbond direction will make the Hbond weaker. Again, how much it depends on those two quantities.

Hope this helps!

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