ABSTRACT
An alternative expression was proposed by Sendin and Rowlen [247], who measured adhesion forces with A F M under ambient conditions. The authors studied the nature of the pull-off force on a variety of surfaces as a function of relative humidity. A mathematical model of pull-off force as a function of relative humidity was proposed in which the chemical specificity was explained. The proposed form of the relationship between measured pull-off force and relative humidity is
(36)
where F s t v is the surface-tip adhesion force in the presence of water vapor, F s t w is the surface-tip adhesion force in the presence of liquid water, Fcap is the adhesion force due to capillary condensation, pf/p's is the relative humidity at the transition point between the two regimes and m is the slope of the transition. The capillary force may be calculated as the sum of force due to surface tension (Ft) and the force due to a pressure difference across a sphere's surface (F p) [248].
