Dynamics of wetting on smooth and rough surfaces.pdf

Progress in Colloid & Polymer Science Progr Colloid & Polymer Sci 74:69-75 (1987)
Dynamics of wetting on smooth and rough surfaces
. Cazabat and . Cohen Stuart
Coll~ge de France Physique de la mati~re condens6e, Paris, France
Abstract: The rate of spreading of non-volatile liquids on smooth and on rough
surfaces was investigated. The radius of the wetted spot was found to agree with
recently proposed scaling laws (t 1/1~ for capillarity driven and t 1/8 for gravity
driven spreading) when the surface was smooth. However, the crossover between
these regimes was not observed at a constant value of the radius. Rough surfaces
exhibited at least four spreading regimes which could be rationalized in terms of
a macroscopic contact angle and macroscopic deviations thereof. An interesting
feature is the appearance of a wetted rim around the central drop. This rim
follows a diffuce spreading law (tl/2). Partially wetting liquids followed the
same dynamics provided the spreading conditions was fulfilled.
Key words: _Wetting dynamics, smooth and rough surface, silicone oils
Introduction I. Theoretical predictionsfor spreading on smooth
surfaces
Because of their practical importance, wetting
phenomena have raised many questions for a long Let us consider a drop of a non-volatile liquid
time. Moreover, the subject has been more recentl