Capillary action for non-polar substances?

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Discussion Overview

The discussion revolves around the phenomenon of capillary action, particularly in relation to non-polar substances like ether. Participants explore the underlying intermolecular forces and the conditions necessary for capillary action to occur, questioning established notions and examining various theoretical frameworks.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about capillary action, asserting that non-polar substances should not exhibit this behavior, yet observes ether climbing a paper towel and questions the intermolecular forces involved.
  • Another participant counters that polarity is not binary and suggests that diethyl/methyl ether has polar characteristics, highlighting dipole-dipole interactions and London forces as relevant factors.
  • A third participant seeks clarification on the reasoning behind the belief that non-polar substances cannot undergo capillary action.
  • There is a suggestion that hydrogen bonds and dipole-dipole forces are responsible for capillary action, indicating a need for further exploration of these interactions.
  • A later reply discusses the lack of a comprehensive microscopic theory for adhesion, adsorption, or wetting, referencing historical work and noting the complexity and unresolved nature of the topic, including various theoretical models and the singularity at the contact line.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are multiple competing views regarding the role of intermolecular forces in capillary action for non-polar substances, and the discussion remains unresolved.

Contextual Notes

The discussion highlights limitations in existing theories and the complexity of the interactions involved in capillary action, particularly for non-polar substances. There is an acknowledgment of the ongoing debates and the lack of conclusive evidence in the literature.

Archosaur
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I thought I understood capillary action, but according to my understanding, non-polar substances shouldn't undergo capillary action. Today in lab, we were working with ether, which is non-polar, and I noticed it climbed up a paper towel. It was slower than water, but still... what intermolecular forces pulled the ether up the towel?

Or is my understanding of capillary action wrong? Are intermolecular forces necessary? They must be!
 
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Polarity is not a binary property. Diethyl/methyl ether is actually fairly polar. So to begin with: Dipole-dipole interactions. Also, London forces.

If there were no (or little) intermolecular forces, it wouldn't be a liquid.
 
Archosaur said:
I thought I understood capillary action, but according to my understanding, non-polar substances shouldn't undergo capillary action.

Why do/did you think this?
 
Aren't hydrogen bonds / dipole-dipole forces responsible for capillary action?
 
Ah. Actually, we do not yet have a microscopic theory for adhesion, adsorption, or wetting. Girifalco and Good did some seminal work in the late 1950's using the Lewis acid-base formalism, but Lee (in "Contact Angle, Wettability and Adhesion", VSP 1993) identified two main theoretical formalisms (so-called Surface Tension Component and Equation of State), and identified 6 molecular interactions (electrostatic, charge transfer, exchange-respulsion, polarization, dispersion, coupling) that go into the different models. It's been a long time since I got into detail about this; the field has hopefully advanced in the meantime.

There's a huge amount of literature on this subject; none of it is conclusive and none of it is valid for more than a few very special cases- long chain polymers, for example.

Even worse, the problem of wetting leads to an irreducible singularity at the (moving) contact line). This problem has not been resolved. Shikhmurzaev's "Capillary flows with forming interfaces" is a good summary of the current state of the art regarding this problem.
 

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