I have two samples with different O/C ration. one of them has bigger O/C ratio but it is less hydrophilic and water contact angle (WCA) is less than another sample.they have different percent of oxygen functional groups, so I think maybe some specific groups have more effect on wettability than O/C ratio.
What kind of surfaces? How do you measure your advancing and receding angle (conditions, roughtness, homogenity, pretreatment)?
Why should the O/C be a correct marker for polarity or water-surface interactions.
oxygen ratio and crystal structure definitely has effect on contact angle. surface on Talc (mineral) is Si-O bond, the same as quartz, but Talc is naturally hydrophobic due to tetrahedral structure of Si-O system, while Quartz is hydrophilic. "BUT" in order to determine this on the surface of your sample, the method, hysteresis, chemical composition at the surface, hydrogen bonds, etc should be taken into consideration!
There are a number of papers looking at C/O functionalities and their effect on surface wettability. One thing to also bear in mind is the surface roughness of your samples as this may also cause differences to measured contact angle. We used XPS to determine functional groups present and measured contact angles for various C/O concentrations and functional group distributions. This was backed up with AFM measurements to ensure that the surface roughness was not the driving factor for conatct angle changes.
You can look at this paper:
Surface studies of low molecular weight photolysis products from UV-ozone oxidised polystyrene, Surface Science 581 (2005) 169–177
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