Anti-icing performance of superhydrophobic surfaces

Abstract

This article studies the anti-ice performance of several micro/nano-rough hydrophobic coatings with different surface chemistry and topography. The coatings were prepared by spin-coating or dip coating and used organosilane, fluoropolymer or silicone rubber as a top layer. Artificially created glaze ice, similar to the naturally accreted one, was deposited on the nanostructured surfaces by spraying supercooled water microdroplets (average size ∼80 μm) in a wind tunnel at subzero temperature (−10 °C). The ice adhesion strength was evaluated by spinning the samples in a centrifuge at constantly increasing speed until ice delamination occurred. The results show that the anti-icing properties of the tested materials deteriorate, as their surface asperities seem to be gradually broken during icing/de-icing cycles. Therefore, the durability of anti-icing properties appears to be an important point for further research. It is also shown that the anti-icing efficiency of the tested superhydrophobic surfaces is significantly lower in a humid atmosphere, as water condensation both on top and between surface asperities takes place, leading to high values of ice adhesion strength. This implies that superhydrophobic surfaces may not always be ice-phobic in the presence of humidity, which can limit their wide use as anti-icing materials.

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.