Experimental investigation on the wetting behavior of a superhydrophobic surface under controlled temperature and humidity

Abstract

Superhydrophobic surfaces (SHS) are of great interest in various industrial fields. However, the application of these surfaces in cold, humid and submerged environments (as in the case of ice slurry production) sometimes presents problems related to the loss of their superhydrophobic properties. This paper presents an experimental study in order to characterize the wetting behavior of a surface coated with a commercial superhydrophobic "Ultra Ever Dry" (UED) coating at different surface temperatures (from 22 °C to − 13 °C) and relative humidity (13%, 20%, 30%, 40% and 50%). Three methods are developed to characterize the wetting behavior. The first method consists in depositing a water drop on the cooled superhydrophobic UED surface. The objective is to characterize the static wetting behavior (evolution of contact angles) during the cooling of the surface for different relative humidity. The second method consists in dropping a water drop on the cooled UED superhydrophobic surface with an impact velocity of 1 m s−1. This method allows the dynamic behavior of the wetting (impact and rebound of the drop) to be characterized at different temperatures. The third method, consists in studying the effect of the immersion of the SHS in a volume of water cooled until supercooling then freezing. The aim is to analyze the wetting behavior in immersion at low temperature. The results of the static wetting study show that the superhydrophobic coating loses its non-wetting properties at temperatures below 13 °C for a relative humidity between 13% and 50% due to condensation on the surface. The results of the dynamic wetting study show that the superhydrophobic coating has poor resistance to water drop impact at surface temperatures below 4 °C. The wetting transition from Cassie to Wenzel state in low temperature immersion is caused by ice formation. The wettability state influences the morphology of the ice produced after freezing.