Patterned thin water films on mica

Patterned water films were formed on the surface of mica by contact with clean, patterned poly(dimethylsiloxane) stamps in ambient humidity. Capillary condensation of ambient atmospheric water in the stamp channels allowed transport of potassium from the mica surface to the stamp, which locally modified the wetability of the mica surface. The resulting mica surface was imaged with contact-mode atomic force microscopy, revealing 3 Å-tall patterns. The pattern disappeared as the relative humidity was decreased (<25% RH) but reappeared as the relative humidity was increased above ∼35%. The pattern also disappeared as the relative humidity was increased above ∼70% but again reappeared when the humidity was subsequently decreased to ∼35%. This high-humidity treatment often resulted in patterned 1 nm-tall islands on the mica surface, which are believed to be a potassium compound (possibly potassium bicarbonate). Such regularly patterned films may be useful as models of heterogeneous surfaces that can be used for fundamental wetting studies and as templated reaction spaces for aqueous materials synthesis.