Environmental scanning electron microscopy of water condensation on superhydrophobic and fluorinated superoleophobic micro-rough aluminum surfaces is reported. We observed film-wise condensation on superhydrophobic surfaces and pronounced drop-wise condensation on the superoleophobic surfaces, possessing the similar topography.
Nano- and micro-scaled surfaces are of much industrial interest in a view of their numerous applications as water-repellent (self-cleaning) [1], superoleophobic [2] and ice-phobic surfaces [3]. This paper is focused on water condensation on micro-scaled aluminum surfaces. Water condensation could be generally classified as drop-wise and film-wise. In our investigation, we focus on the possibility of fine tuning of surface properties of aluminum micro-rough surfaces enabling switching from film-wise to drop-wise pathway of water condensation and on the kinetics of growth of droplets. Water condensation was studied on superhydrophobic and superoleophobic micro-rough aluminum surfaces of the same topography. The difference in the pathways of condensation was attributed to the various energy barriers separating the Cassie and Wenzel wetting states on the investigated surfaces. The higher barriers inherent for superoleophobic surfaces promoted the drop-wise condensation.
The structures were studied in the Quanta 200FEG ESEM (Environmental Scanning Electron Microscope) while imaging the sample surface using the gaseous secondary electron detector. In-situ imaging of water condensation was performed within the ESEM at wet-mode using water vapor from a built-in distilled water reservoir. ESEM study shows the very different pathways of condensation processes on the micro-scaled chemically modified superhydrophobic and superoleophobic surfaces.
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3. Hejazi, K. Sobolev, M. Nosonovsky, From superhydrophobicity to icephobicity: forces and interaction analysis, Sci Rep. 3 (2013) 2194.
