Anti-icing performance of superhydrophobic surfaces
Research highlights
► A number of superhydrophobic samples were prepared. ► Their anti-icing performance was tested on “dry” and “wet” surfaces. ► Their anti-icing performance was tested as a function of icing/deicing cycles.
Introduction
Ice and wet-snow adhesion and excessive accumulation on exposed structures and equipment is well known to cause serious problems in cold-climate regions [1], [2], [3], [4]. Atmospheric icing occurs when super-cooled water droplets (or snow particles) come into contact with the surface of exposed structures, which may lead to material damage and socioeconomic costs in many sectors of the economy, including power transmission and distribution, telecommunication networks, aircraft, boats, etc. [2], [3]. Each year, numerous failures due to ice accumulation are reported in Iceland, Norway, Canada, Finland, the US, Russia, and even in Japan and China [1], [2], [3], [4], [5]. To counter this problem, various de-icing and anti-icing techniques have been developed over the past few decades [2], [3]. Among those, ice-repellent coatings have been recently proposed as a passive technique to reduce or prevent ice accumulation on the outdoor structures. Such coatings provide reduced adhesion or delay water freezing on their surface [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], which is expected to result in lower ice or wet-snow accumulation on such coated surfaces [7], [15]. Therefore, the research on coatings capable of reducing wet-snow, frost, or ice accumulation has been going on for several decades [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25].
Superhydrophobic surfaces, i.e. those characterized by water contact angle (CA) above 150° and low CA hysteresis (CAH), were first tested by Saito et al. [5] and showed promising anti-icing performance. More recently, other groups showed reduced ice adhesion [6], [8], [11], [12], [13] or delayed water freezing [7], [24], [26], [27] on rough superhydrophobic surfaces. These two characteristics make superhydrophobic surfaces attractive candidates for anti-ice applications, i.e. where reduced ice/snow accumulation is needed. However, the ice-releasing performance of rough superhydrophobic surfaces has not been adequately studied yet in different conditions.
In this work, we prepared several nanostructured superhydrophobic coatings with different chemistry and topography and tested them as anti-ice candidate materials. The glaze ice accumulated on the samples was prepared by spraying supercooled water microdroplets in a wind tunnel at subzero temperatures. Such conditions thus simulated most severe natural atmospheric icing. The samples were tested over numerous icing/de-icing cycles in order to assess the durability of their ice-releasing performance. Also, ice adhesion was evaluated on the samples previously placed on a cold surface to condense water, i.e. on ‘wet’ surfaces.
Section snippets
Experimental
Table 1 gives a brief description of the samples prepared and tested in this study. Aluminium alloy (AA6061) plates, 3.2 cm × 5.0 cm in size, were used as substrates. Sample A was prepared by spin-coating a CeO2 nanopowder suspension in Zonyl 8740 (perfluoroalkyl methacrylic copolymer soluble in water, DuPont). This process has been already described somewhere [6], [8], [28]. In brief, CeO2 nanopowder, with particle size <50 nm from Aldrich (8.0 g), was mixed with 80 ml of deionized water. The
Results and discussion
Fig. 1 shows the surface images of samples A–D, and Table 1 exhibits both CA and CAH values of the samples. All the samples were found to be rough at micro/nano-scale. Thus, air was expected to entrap into such structures during wetting. As a result, the Cassie wetting mode was expected for these samples with high surface roughness and low-energy top layers [7], [14], [19], [23], [31], [32], [33], [34]. The water–solid contact area on these samples was expected to be small, which is consistent
Concluding remarks
This paper raises doubts about the wide use of nano-structured superhydrophobic coatings as universal anti-icing materials. We studied ice-repellent performance of several superhydrophobic coatings based on different materials, while the glaze ice used in tests was prepared under conditions similar to those in nature. The results of ice adhesion strength evaluation, after as many as eleven icing/de-icing cycles, showed that the anti-ice performance of the samples significantly deteriorated.
Acknowledgments
The authors thank F. Arianpour (Univ. of Quebec) and Dr. A. Safaee (Queen's Univ.) for their help with some experiments.
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