Superhydrophobicity of Biological and Technical Surfaces under Moisture Condensation: Stability in Relation to Surface Structure

Abstract

The stability of superhydrophobic properties of eight plants and four technical surfaces in respect to water condensation has been compared. Contact and sliding angles were measured after application of water drops of ambient temperature (20 degrees C) onto cooled surfaces. Water evaporating from the drops condensed, due to the temperature difference between the drops and the surface, on the cooled samples, forming "satellite droplets" in the vicinity of the drops. Surface cooling to 15, 10, and 5 degrees C showed a gradual decrease of superhydrophobicity. The decrease was dependent on the specific surface architecture of the sample. The least decrease was found on hierarchically structured surfaces with a combination of a coarse microstructure and submicrometer-sized structures, similar to that of the Lotus leaf. Control experiments with glycerol droplets, which show no evaporation, and thus no condensation, were carried out to verify that the effects with water were caused by condensation from the drop (secondary condensation). Furthermore, the superhydrophobic properties after condensation on cooled surfaces from a humid environment for 10 min were examined. After this period, the surfaces were covered with spherical water droplets, but most samples retained their superhydrophobicity. Again, the best stability of the water-repellent properties was found on hierarchically structured surfaces similar to that of the Lotus leaf.

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate

“…Synthetic superhydrophobic surfaces should also be anti-dew to be of practical use in natural environments, and the anti-dew property has already been demonstrated with properly designed (biomimetic) nanostructures. Indeed, the jumping phenomenon has been reported on a variety of natural surfaces including lotus leaves, lacewings, and springtails (28)(29)(30) as well as on synthetic superhydrophobic surfaces such as nanotextured silicon, aluminum, and copper (31)(32)(33). Note that the nanostructures (particularly the conical protuberances in Fig.…”

Condensation heat transfer on superhydrophobic surfaces

“…Vapor condensation is a ubiquitous phenomenon occurring in nature [1][2][3][4][5] . We observe this process in our daily lives, such as on a hot summer day when water accumulates on a cold drink or when fog forms on a humid day.…”

Water condensation on zinc surfaces treated by chemical bath deposition

“…In contrast, and although this process is of major importance for the evaluation of corrosion, the studies of condensation-induced wetting on superhydrophobic surface and their corresponding wetting properties (self-cleanliness, different wetting states), are much less documented [18][19][20][21][22][23][24][25][26][27][28][29]. The aim of the present work is thus to study condensation of water on a multiscale rough superhydrophobic surface where the contact angle is varied in a wide range (70-150 • ).…”