title: Vertical water distribution during the drying of polymer films cast from aqueous emulsions.
abstract: We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films, testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile in the vertical direction ( i.e. normal to the substrate). When Pe < 1, the water concentration in films cast from an alkyd emulsion is found via magnetic-resonance profiling to be uniform with depth, which is consistent with expectations. When Pe > 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface layer develops, but particles are not coalesced in this layer to form a continuous "skin", but rather the structure is likely to be that of a biliquid foam.
authors.affiliation: Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK.
authors.forename: J-P
authors.initials: JP
authors.lastname: Gorce
authors.forename: D
authors.initials: D
authors.lastname: Bovey
authors.forename: P J
authors.initials: PJ
authors.lastname: McDonald
authors.forename: P
authors.initials: P
authors.lastname: Palasz
authors.forename: D
authors.initials: D
authors.lastname: Taylor
authors.forename: J L
authors.initials: JL
authors.lastname: Keddie