On-demand evaporation mode of sessile droplet by designing substrate surface wettability patterns

Abstract

A conceptual strategy of controlling the evaporation mode of sessile droplet that is demonstrated by the variation of its contact angle and contact radius through designing the surface wettability pattern of substrate is proposed. A theoretical model is established based on the geometry shape of the droplet and minimization of the total surface free energy of the droplet-substrate system. The model is implemented to predict the variation of the surface free energy during evaporation and is used to determine the time evolutions of the contact angle and contact radius. With this theory, a relationship between surface wettability patterns and droplet evaporation modes is established. Comprehensive molecular dynamics simulations are employed to validate the theoretical predictions, and the evolutions of the contact angle and contact radius during evaporation agree well with the theoretical predictions. The proposed technique to control the evaporation mode of sessile droplets is further implemented to control the deposition pattern of nanoparticles by liquid evaporation, which manifests that the theoretical model established herein could explain the underlying mechanism of controlling evaporation mode of sessile droplets and such method of designing substrate surface wettability pattern has potential applications in inkjet printing, nano-assembly, and nano-device manufacturing.