Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2017 / Paper 1 / Section B / 10 / iii / b

wetting liquid in narrow pores and gaps between fibers can have a concave meniscus. Its signed curvature is negative, so the Kelvin equation permits equilibrium at a vapor pressure below that above a flat liquid surface. capillary condensation in sufficiently small, wettable gaps explains moisture accumulation at high relative humidity. Increased humidity brings the vapor closer to flat-surface saturation and permits condensation in larger gaps. Surface adsorption can precede a bulk-like meniscus; large open spaces do not automatically fill at every humidity. The interpretation assumes a wetting contact geometry and does not require the entire cloth to be below the ordinary planar dew point.