Article pubs.acs.org/Langmuir
Dynamics of Ice Nucleation on Water Repellent Surfaces Azar Alizadeh,*,† Masako Yamada,† Ri Li,† Wen Shang,† Shourya Otta,† Sheng Zhong,† Liehui Ge,‡ Ali Dhinojwala,‡ Ken R. Conway,† Vaibhav Bahadur,† A. Joseph Vinciquerra,† Brian Stephens,§ and Margaret L. Blohm† †
General Electric Global Research, Niskayuna, New York 12309, United States Department of Polymer Science, The University of Akron, Ohio 44325, United States § GE Aviation, Cincinnati, Ohio 45215, United States ‡
S Supporting Information *
ABSTRACT: Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water−surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water−substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air−water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.
1. INTRODUCTION Ice accretion on surfaces of aircraft, wind turbine blades, oil and gas rigs, heat exchangers, transmission lines, boats, buildings, and other infrastructure presents long recognized problems with respect to safety, efficiency, and cost of operation.1−7 Current active ice mitigation approaches are often based on melting or breaking of already formed ice layers. In addition to their undesired weight and design complexity, active antiicing approaches require substantial energy for their operation.3−7 Passive icephobic (low ice adhesion) coatings have also been proposed during the past 5 decades, yet their performance has often been suboptimal. 4,8−13 Both passive and active approaches rely on the removal of a finite ice layer; measuring and controlling the thickness of this layer are yet other challenges. Development of coatings that limit and ultimately prevent ice accretion on their surfaces is desirable and has been the subject of considerable recent attention.14−23 This interest has been sparked by the remarkable water repellent properties of superhydrophobic surfaces.24,25 The strength of ice adhesion to a flat surface decreases with increasing hydrophobicity.26−28 Therefore, ice is expected to adhere very weakly to superhydrophobic surfaces with water contact angles > 150°. © 2012 American Chemical Society
Paradoxically, some authors have shown that ice adhesion increases with surface roughness,27 while others have shown up to 18-fold reduction of ice adhesion strength on superhydrophobic surfaces.19,20 Recently, Mishchenko et al. have shown that water droplets impinging on superhydrophobic surfaces exhibit nonicing behavior if the time scale of droplet wetting and retraction from the surface is smaller than the ice nucleation time.14 These authors offer an analysis of icing through visual examination of supercooled droplets and firstorder modeling of icing under droplet impact. Cao et al.17 have reported that superhydrophobic surfaces exhibit icephobic properties under water impact conditions, but only if the surface texture dimensions fall within a critical size regime. Surprisingly, the critical size regime suggested by Cao et al.17 for nonicing behavior (
