- #1

Bacat

- 151

- 1

I can correlate the surface tensions with the pore sizes and that's interesting, but I want to explain them also. I believe I can explain the hydrophobicity of micropores (about 10 angstroms in width or less) by arguing that the capillary pressure in them is too high to allow water to penetrate at atmospheric pressure. My question is how to calculate this pressure.

I know that capillary pressure is:

[tex]P_c=\frac{2 \gamma Cos\theta}{r}[/tex]

where gamma is surface tension of the liquid, theta is the contact angle of the liquid at the solid interface, and r is the radius of a pore. I'm not sure how to calculate the contact angle for a powder given a known gamma. Is this the wrong approach?

I'm also not clear what the balancing force should be. I want to find the pore size which forbids entry of the fluid into the pore for a given gamma. I am assuming atmospheric pressure, so do I just need to find the r that makes P_c equal to P_atm?

Can I choose an arbitrary contact angle and get a reasonable estimate?