Evaporation and particle deposition of bi-component colloidal droplets on a superhydrophobic surface

Abstract

Droplet evaporation is not only a natural phenomenon occurring on a daily basis, but also a novel approach to pattern microscopic structures using small colloids via the evaporative self-assembly. In this work, we carry out a comparative investigation of the evaporation kinetics and particle deposition dynamics of diverse bi-component colloidal droplets on a superhydrophobic surface. We found that the evaporation modes of a drying droplet are determined by both the added volatile component and dispersed colloidal particles, which affect the droplet-surface interactions and thus the contact line motion. While increasing the concentration of the volatile component significantly accelerates the evaporation, no apparent influence was observed for the presence of colloidal particles on droplet lifetime, and the evaporation rate of bi-component droplets in the constant contact angle and constant contact radius modes can still be described by their classical theories for single component droplets. Three types of deposition patterns, namely, a thin disk, a three-dimensional cap and a circular ring, were obtained after evaporation. By direct visualizing the particle aggregation process and analyzing the evaporation flux distribution around sessile droplets, we demonstrate that the residual colloidal structures are regulated by the capillary flows developed in the evaporating droplets.