Surface tension between water and air is caused by the attraction forces acting on the molecules of the liquid. A contact angle is the angle between the edge of the meniscus and the sold material, hydrophilic for <90, hydrophobic >90.

Related References

book Adsorption, surface area and porosity, 2ed, by Gregg, S.J. and K. S. W. Sing, 1982 detail summary of basic capillary theory Methods of measuring the moisture diffusivity at high moisture levels, by Janz, M., 1997 forces in rainscreen leakage Water flow by means of capillary action, by Air-Ins inc, 1997