Capillary action for non-polar substances?

[Archosaur]

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!

 

[alxm]

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.

 

[Andy Resnick]

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?

 

[Archosaur]

Aren't hydrogen bonds / dipole-dipole forces responsible for capillary action?

 

[Andy Resnick]

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.