Fluid In The Rough Solid Surface Infiltration And Its Hysteresis

The work discusses various wetting phenomena occurred in liquid-solid contacts. It starts from the Laplace equation of a two-phase interface, to the Young equation of three-phase contact line, as well as some modifications on the Young equation appeared in literature. Highlights are made on controversial points, that are worth to be further investigated. Especially, contact angle of a real three-phase system is usually not, as predicted by the Young equation, defined uniquely, but varies in a range of values-the phenomenon known as hysteresis of the contact angle. When the hysteresis happens, the contact and wetting properties become complicated, of which mechanism, in particular a thermodynamically based explanation, is yet not fully clear by now.In 1925 Adam and Jessop introduced the well known notion of static force of friction to explain phenomenologically the hysteresis of the three-phase contact angle, that satisfies a Mises-like yield law. In this paper which focuses on influence of surface roughness on the wetting angle, the possibility for describing the contact friction with another frequently used friction law is studied, namely the Amonton yield condition. Using the recently reported data on stainless steel and polypropylene samples as example, we compared the surface-tension coefficient given by the Mises-like law and Amonton-like law. It is found that only the latter possesses always the Wenzel behavior, which claims an increasing of the tension coefficient with surface roughness, as well as total wetting condition, namely receding angle vanishes when the surface-tension coefficients of solid-liquid and solid-vapor become equal.The result shows that the Amonton-like law seems to be more reasonable for describing the static friction of contact lines than the Mises-likelaw.As to now, compare others' used Mises-like law, it's a new idea.Oppugning the existent thermodynamic explanation of contact angle hysteresis , we point out its irrationality, and call on a strict wetting thermodynamic to explain it.