Anti-icing approach on flexible slippery microstructure thin-film

Highlights

• New facile method for the anti-icing approach by combining the microstructure with the lubricant infusing.

• The Slippery Microstructure Ecoflex indicated the advantages in adhesive strength, freezing time, and ice-repellency.

• A theoretical model has been proposed to predict the freezing time.

Abstract

In this study, we examine the anti-icing performance on the flexible slippery microstructure thin film in terms of adhesion strength, freezing time, and ice-repellent efficiency. Ecoflex was mixed with low surface tension lubricant to achieve the slippery property. Besides, a process of combining the dry etching and spin coating was used to generate a microstructure on the elastomer thin film. The anti-icing performance on the functionalized sample was then compared with the non-slippery substrates and demonstrated the advantages of the flexible slippery microstructure elastomer in all mentioned properties. In addition, a theoretical approach was used to predict the freezing time of a static droplet. This insight offers a new facile method and design of icephobic surfaces for outdoor applications.

Introduction

Icing related problems are a significant challenge in transportation safety. Ice accumulation on aircraft's wings may lead to disastrous crashes due to the lack of lift force (Tran et al., 1995). Ice accretion on energy transmission systems sometimes causes a massive collapse due to weight overloading, endangering people, and vehicles underneath (Farzaneh, 2000). Additionally, ice growth on railways, offshore platforms, and shipboards can produce heavy devastation and conduce dangerous accidents (Milaković et al., 2019; Wang et al., 2019; Landy and Freiberger, 1968). Therefore, anti-icing processes are intensively investigated to reduce unexpected damages. While anti-icing active methods involve the removal of ice using external energy to remove ice bulks (Palacios et al., 2011; Makkonen et al., 2001), the passive approaches aim to hinder the formation of ice crystals without external energy and achieved by physicochemical methods (Wang et al., 2018a; Wang et al., 2018b; Zhang et al., 2015). Among reported passive methods, superhydrophobic surfaces (SHs) have been deeply examined for several decades and are considered a promising strategy for anti-icing applications based on their unique characteristics in water repellency. Many studies have been carried out to optimize anti-icing performance on SHs, including reducing the ice-surface adhesion strength (Meuler et al., 2010; Yao et al., 2019; Jafari et al., 2019) and delaying the freezing time (Guo et al., 2019; Adanur et al., 2019; Grizen et al., 2019). However, recent studies have revealed that SHs may not always be the solution for anti-icing applications due to sensitivity to frost and mechanical interlocking effect (Bengaluru Subramanyam et al., 2016; Chu et al., 2017; Esmeryan, 2020). Water intrusion involves deeply anchoring formed ice to micro/nanostructures, which makes it harder to remove and consequently deteriorates the hydrophobic coating (Jung et al., 2011).

Inspired by the Nepenthes pitcher plant (Bohn and Federle, 2004), Biomimetic Slippery Lubricant-Infused Porous surface (SLIP) has attracted attention and is believed to be an innovative anti-icing strategy (Zhu et al., 2013; Dou et al., 2014; Ozbay et al., 2015; Ozbay and Erbil, 2016; Erbil, 2016; Yildirim Erbil, 2019; Yeong et al., 2016; Vogel et al., 2013; Kim et al., 2012; Wong et al., 2011). This new concept introduces a defect-free smooth liquid with superior properties of water repellency, self-healing, and humidity tolerance. Water droplets are elevated and isolated with surface features due to the immiscibility of water and lubricant, finally facilitating the loose interaction between substrate and formed ice (Dou et al., 2014; Ozbay et al., 2015; Erbil, 2016; Yildirim Erbil, 2019; Yeong et al., 2016; Kim et al., 2012; Nguyen et al., 2019a). A SLIP surface can be achieved by combining a porous structure with a low-surface-tension liquid which are both immiscible in water and easily deposited on rough surfaces. There are various methods to generate micro/nanostructure including: lithography (Subramanyam et al., 2013), particle coating (Chu et al., 2017), and dry/wet etching (Nguyen et al., 2019a; Stamatopoulos et al., 2017). Various types of lubricant materials have been utilized such as silicon oil, FC – 70, Kerosene, or Krytox with different characteristics (Nguyen et al., 2019a; Wang et al., 2016).

To the best of our knowledge, there is no study until now concerning the incorporation of slipperiness and uniform structure for anti-icing purposes. We believe that the optimized textured structure contributes significantly to both adhesion strength and freezing time criteria. In this work, the anti-icing performance was emphasized by combining the surface roughness and the original slippery property of an infused lubricant. A Slippery Microstructure Ecoflex (SME) thin film was fabricated by depositing a mixture of Ecoflex and Silicon oil on Polyimide (PI) negative mold, which was created from a parent uniform quartz microstructure. After curing for solidification, sample was peeled off and naturally dried in ambient air. SME thin-film consists of a uniform array of cylinder shape Ecoflex pillars with Silicon oil diffused inside. In this work, an appropriate concentration of Silicon oil (20% w.t.) was used to maintain the elastic modulus of the sample. Such a combination was used to quantitatively examine the integrated contribution of surface roughness and slippery property in anti-icing performance. Real-time tests including adhesive strength, freezing time, and ice-repellent effectiveness were conducted on SME, Micro-pillar Ecoflez (ME), flat Ecoflex, and as-received bare quartz. Our results support and highlight the advantages of ME and SME thin film in all mentioned anti-icing terms and illustrate a new facile passive method for icephobic applications.