ABSTRACT
Equation (23) is useful for estimating the capillary force of a micro-contact; note that it is described as dependent only on the surface tension of bulk water and the contact angle, 0, but is independent of the solid-solid and solid-liquid interaction parameters. This equation does not explain the force transition experimentally observed in several papers as a function of the relative humidity. Miranda et al [200] discovered by scanning polarization microscopy that the force instability was caused by a low coverage of water at the solid surface. The authors suggested that water, condensed from water vapor at room temperature on mica, forms a partially developed monolayer of an ice-like phase. They concluded that with decreasing humidity the ice-like water monolayer, which is formed around 90% RH, breaks into islands, until the water coverage is too low (20% RH).
