How does an electric field create velocity in a water bridge?

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Discussion Overview

The discussion revolves around the mechanisms by which an electric field influences the movement of water in the context of water bridges and electrowetting. Participants explore the effects of electric fields on polar water molecules, the role of ionic species, and related phenomena in fluid dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about how water moves in an electric field, noting that polar molecules can only rotate.
  • Another participant suggests that polarization of water molecules may lead to a net force due to the proximity of charges, comparing it to Van der Waals forces.
  • A third participant introduces the concept of autoionization in water, explaining that the resulting ionic species can migrate under an electric field, which may contribute to the movement of water.
  • A fourth participant references an article discussing the dynamics of droplets on hydrophobic surfaces in an electric field, mentioning various forces at play, including electric field force and surface tension, which may relate to electrowetting.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the mechanisms at play in the movement of water under an electric field, and the discussion remains unresolved with no consensus reached.

Contextual Notes

There are limitations in the discussion, such as the dependence on definitions of terms like "polarization" and "net force," as well as the complexity of the ionic species involved in water's behavior under electric fields.

HelloCthulhu
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I've been researching water bridges and electrowetting to learn the effects of electric fields on water molecules but something continues to confuse me: if polar molecules can only rotate in an electric field, how is the water moving? Anyone familiar with this phenomenon? Any help is greatly appreciated!

https://www.academia.edu/18092509/B...trohydrodynamics_of_the_floating_water_bridge
 
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Quick guess is that the polarization places negative or positive charges closer to the source of the electric field, causing the molecules to experience a net force. Similar to the Van der Waals force between closely spaced atoms/molecules. Not sure if that's correct or not, so I hope someone with more knowledge on the topic can answer.
 
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Water (even completely pure water) isn't just water molecules. It undergoes a process called autoionization, which very simplified looks like
$$2H_2O \rightleftharpoons OH^-+H_3O^+$$
with the caveat that these species are actually significantly more complicated than the above equation makes them seem. The point is that water self-ionizes (this is the reason that water has a pH at all), and it is these ionic species that migrate under the influence of an electric field.
 
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I'm not sure if this will help, but this article, "Dynamics Behaviors of Droplet on Hydrophobic Surfaces Driven by Electric Field" (2019), describes in section 3. Results and Discussion that a water droplet on a substrate within an electric field is "mainly affected by the inertial force, viscous force, electric field force, surface tension and substrate adhesion". Granted the surfaces are hydrophobic, but I thought the data might still be useful since I'm interested in electrowetting as well.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6915515/
 

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