Effects of Structural Topography on Nanofluids Droplet Evaporation on Multifarious Superhydrophobic Surfaces

In this paper, we experimentally studied the evaporation kinetics and wetting dynamics of nanofluid sessile droplets on microstructured superhydrophobic surfaces of a constant air fraction but different structural topographies including arrays of pillars, lines, and wells. The dissimilar superhydrophobic surface patterns were fabricated on a silicon substrate by photolithography and deep reactive ion etching (DRIE) followed by Teflon coating. The 0.01wt% suspensions of gold (Au) nanoparticles of 250 nm in diameter were tested as nanofluids. The change of contact angle, base diameter, height, volume, and evaporation rate of the evaporating nanofluid droplet was measured in a room condition by using a goniometer. The results show that the change of structural topographies, despite the same air fraction on the surface, make significant difference in the droplet profile evolution during sequential evaporation phases. Compared to pure water tested as control, the distinctive influence of nanoparticles was especially observed in the final pinning phase with the tested nanofluid condition. This paper demonstrates that the evaporation kinetics and wetting dynamics of liquid droplets are significantly affected by the structural topography and the presences of nanoparticulates, which should be considered in the design and applications of superhydrophobic surfaces for droplet-based heat and mass transfer systems.