| In this talk I will review x-ray scattering and non-contact AFM measurements from equilibrium liquid films and drops on nanopatterned surfaces, both chemical and topographical. Here the features are as small as 20 nm with a periodicity as small as 40nm are utilized. For studies on chemical patterns, the height and shape of the condensed drops have been measured using AFM. For sufficiently small drop sizes, the surface energy associated with the curvature reduces the nanodrop’s height relative to a flat wetting film. Under saturated conditions, our results show that the height of the drops scales as the square root of the width of the chemical features, in good agreement with theory. The stability of thin wetting films has also been investigated on chemically patterned surfaces. Our results show that films spanning the entire pattern are only stable for thicknesses in excess of a critical value hc whereas thinner films spontaneously dewet the partially wettable regions of the substrate. The critical thickness hc increases linearly with the width of the partially wettable stripes in good agreement with an interface displacement model derived from microscopic density functional theory. The equilibrium filling/wetting of nanogrooves with an organic liquid have also been investigated using x-ray scattering methods, both in transmission and reflection geometries. Our results show deviations with respect to a simple geometric filling model based on the Kelvin Equation and are in good agreement with DFT calculations. A new surface x-ray scattering technique for studying topographical surfaces that eliminates the strong refraction and reflection terms inherent in grazing incidence x-ray scattering measurements will be discussed and this should allow a direct determination of the meniscus shape. I will also show how similar nanopatterned surfaces can be used to make ultrahydrophobic surfaces. These in-situ x-ray results clearly show that air must be trapped in the cavities and that the penetration of the water into the cavities is 7 +/- 3nm, independent of the cavities depth. In collaboration with Antonio Checco, Tommy Hofmann, Chuck Black and Kevin Yager (BNL) and Mykola Tasinkevych and Siegfried Dietrich (Max-Planck-Institute, Stuttgart) |
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