Non wetting surfaces

F ure 3.5 Contact angle of a liquid on wetting and non-wetting surfaces. Yoni -Laplace Equation... 

Currently, however, quantitative assessment of the mechanical durability of non-wetting surfaces is difficult due to the diversity of wear testing and characterization methods discussed above. Ideally, the evaluation techniques should be more standardized and possibly reduced in number, as this would be beneficial for focused efforts to develop resilient coatings. From all the techniques that we described above, there seem to be some of them that are more commonly accepted. Linear abrasion, for instance, seems to be a very well accepted and is a common method to evaluate the mechanical durability. Sand, water/jet and gas impact are also good techniques to evaluate the stability of the surfaces for outdoor applications. Nevertheless, the range of possible applications for super hydrophobic surfaces may call for specialized mechanical tests like laundry tests, finger touch, etc. 

An overall catalyst effectiveness factor no can be derived to take into account the effective surface wetting and the external reactant supply. This factor is defined as the ratio of the actual conversion rate and that obtained without diffusion resistance. This overall effectiveness factor may be approximated by the weighted average value for the differently wetted fractions of the pellet surface (Capra et al. [8]). If the wetting situation can be simplified into one wetted and one non-wetted surface fraction, with pellet volume fractions equivalent to surface fractions, then ... 

Choi W, Tuteja A, Mabry JM, Cohen RE, McKinley GH (2009) A modified Cassie-Baxter relationship to explain contact angle hysteresis and airisotropy on non-wetting surfaces. J Colloid Interface Sci 339 208-216... 

---