Angles and Wettability

For liquid and vapour in equilibrium, these values of AG are equal and 2ViY 2  

The Kelvin equation can be applied to the solubility of spherical particles by replacing the ratio plp by a/ o where is the activity of dissolved solute in equi- 

Finally, for very small droplets, there can be an influence of the radius of curvature on the surface tension itself. The Tolman equation shows one possibility for this  

This equation is for pure liquid droplets of radius r, where Yo is the surface tension in the limit of r - oo and 5 is the Tolman length. Although derived thermodynamically rather than empirically, there continues to be some debate over the sign and magnitude of the Tolman length, and the droplet size below which the equation applies [31]. 

When a drop of liquid is placed on a solid surface, the liquid may form a bead on the surface or it may spread to form a film. A liquid having a strong affinity for the solid, that is, if its surface tension is less than the critical surface tension of the surface, y, will seek to maximize its contact (interfacial area) and spread to form a film. A liquid with much weaker affinity, that is, if its surface tension is above y., will form into a bead. The critical surface tensions of solids range from 18 mN m for Teflon to about 46 mN m for nylon. 

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A reversible photocontrol of wettability of polymeric materials is possible by a technique developed by Irie and Iga When a copolymer of butyl methacrylate and (2-hydroxyphenyl)-a-(4-vinylphenyl)benzyl alcohol is irradiated with ultraviolet light, fliere is a large increase in the contact angle and wettability of the material. This reverses back to the original structure in the dark... 

Hansen, G Hamouda, A.A., and Denoyel, R. (2000) The effect of pressure on contact angles and wettability in the mica/water/n-decane system and the calcite + stearic acid/water/n-decane system. Colloids and Surfaces A Physicochemical and Engineering Aspects, 172, 7-16. 

The surface structures are schematically summarized in Figure 7.12 [8]. There are various methods to characterize these surface structures, for example, ultravacuum techniques such as Auger electron spectroscopy and X-ray photoelectron spectroscopy, Raman spectroscopy and infrar spectroscopy, contact angle and wettability, scanning tunneling microscopy, and thermal desorption mass spectrometry. 

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