20 juillet 2012
We study the dynamics of liquid-liquid menisci in a circular tube at small capillary numbers in partial, pseudo-partial and complete wetting conditions. There exists a thin wetting film in the last two situations. By pseudo-partial wetting, we refer to systems having non-monotonic disjoining pressures, as described by Brochard-Wyart et al., Langmuir 7, 335-338 (1991). In this situation, the disjoining pressure allows the coexistence of a microscopic thin film (but not molecular) and a macroscopic contact angle. We measure the meniscus velocity as a function of the pressure drop for different wetting conditions. In pseudo-partial wetting condition, we observe that there is a pressure range where the velocity is extremely low (below 1 ?m/s) but non zero, in contrast with partial wetting, where the meniscus is blocked by a pinned contact line corresponding to the standard contact angle hysteresis. The role of quasi-equilibrium and of surface heterogeneity is discussed to explain the observations.
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