Capturing the evaporation process of water drops on sticky superhydrophobic polymer-nanoparticle surfaces

The evaporation of water drops on sticky superhydrophobic poly(alkyl siloxane) surfaces, which were roughened by adding silica nanoparticles (7 nm) is monitored. Drop evaporation on surfaces corresponding to a high nanoparticle/polymer mass ratio (>0.1) is dominated by the constant contact radius (CCR) mode, with unchanged contact area between the liquid and surface and diminishing contact angle, which is described by the Popov model. The evaporation of drops on surfaces produced by adding nanoparticles at a low concentration (nanoparticle/polymer mass ratio<0.1), starts with the CCR mode, followed by a mixed mode at the later stages of the process. The time over which the CCR mode governs the contact angle variation increases with the nanoparticle concentration.