Growth of a wetting layer in a flowing binary-liquid mixture at bulk coexistence

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Abstract
Using reflectivity, we observe the effect of steady fluid flow on the growth of gravity-thinned wetting films in a binary-liquid system of nitromethane and carbon disulfide at bulk coexistence. The substrate is a horizontal borosilicate glass surface. The growth process is driven by the substrate-liquid interaction and opposed by a gravity-induced pressure gradient. We find that the steady-state wetting-layer thickness increases with the stirring rate in qualitative agreement with the hydrodynamic theory of Kayser, Moldover, and Schmidt [J. Chem. Soc. Faraday Trans. 2 82, 1701 (1986)] for wetting-layer development. We observe diffusion-limited exponential buildup of the wetting layer toward steady state. The steady-stirring experiments presented here are compared with earlier random stirring results. Finally, we find that at high stirring rate the bulk liquid-liquid interface becomes unstable against the formation of liquid droplets. This instability is responsible for a fast growth mode of the wetting layer.