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Publication - Professor Paul Bartlett

    Droplet evaporation

    Colloidal interactions vs. evaporation kinetics

    Citation

    Shafiq, MD, Waggett, F, Norris, E & Bartlett, P, 2019, ‘Droplet evaporation: Colloidal interactions vs. evaporation kinetics’. Colloids and Surfaces A. Physicochemical and Engineering Aspects, vol 578.

    Abstract

    The drying of a colloidal droplet has attracted considerable attention because of its inherent complexity and significance in applications such as coating, printing, and layering processes. There has been great interest in controlling the well-known ‘coffee-ring’ effect, in which the contact line of an evaporating drop is pinned to the substrate so that dispersed particles are deposited onto the three-phase contact line. Large micro-scale convection-driven flows typically determine the structure of the deposited film. Interparticle forces which operate over nanometer-separations, at least in aqueous systems, are relatively unimportant. Our aim is to explore if much longer-range colloidal forces, comparable to hydrodynamic flows, could be used to control particle drying. We generate controllable micrometer-range electrostatic interactions in a suspension by using charge control additives; an anionic surfactant and oil-soluble electrolyte in nonpolar solvents. The drying of droplets containing monodisperse, fluorescent poly-(methyl methacrylate) (PMMA) particles was studied by confocal light scanning microscopy (CLSM). The existence and extent of a ‘coffee-ring’ deposit was characterized. We find that the drying patterns are controlled by a competition between the evaporation rate of the solvent and the strength and range of the electrostatic interactions.

    Full details in the University publications repository