Superhydrophobicity and Icephobicity

Limited robustness is a serious drawback for superhydrophobic coatings and degrades the performance of superhydrophobic surfaces in practical applications. Although fluororeagents have excellent durability for superhydrophobicity, their use has been restricted due to various health and environmental concerns. In this work, we describe a facile and efficient fabrication strategy for creating robust fluorine-free superhydrophobic composite coatings that are prepared by a simple dip-dry method, in which the H 3 BO 3-incorporated SiO 2 −alkyl-silane coatings are deposited on woven cotton fabric surfaces followed by polydimethylsiloxane modification. The coated surface shows a large water contact angle of 157.95 ± 2°and a small sliding hysteresis angle (SHA) of 3.8 ± 0.6°, demonstrating excellent superhydrophobicity. The coated fabric surface also exhibited robustness and durability, withstanding a tape-peeling test (under 48.05 kPa) for around 80 repetitions and sandpaper rubbing (loaded 100 g) for 40 cycles. Furthermore, the coated fabric surface displayed self-healing and oil−water separation capacities. The developed superhydrophobic coatings in this study are robust, environmentally benign, and easy to fabricate, showing promising applications in textile industries.

Micro injection molding is in great demand due to its efficiency and applicability for industry. Polymer surfaces having micro-nanostructures can be produced using injection molding. However, it is not as straightforward as scaling-up of conventional injection molding. The paper is organized based on three main technical areas: mold inserts, processing parameters, and demolding. An accurate set of processing parameters is required to achieve precise micro injection molding. This review provides a comparative description of the influence of processing parameters on the quality of final parts and the precision of final product dimensions in both thermoplastic polymers and rubber materials. It also highlights the key parameters to attain a high quality micro-nanostructured polymer and addresses the contradictory effects of these parameters on the final result. Moreover, since the produced part should be properly demolded to possess a high quality textured polymer, various demolding techniques are assessed in this review as well.

Almost all metals and their alloys are vulnerable to corrosion. To avoid structural damage and to avoid loss of its functionality, the most common protection method used is the application of a coating. In the present work, hydrophobic coatings using modified conducting polyaniline (PAni) were prepared and their corrosion-resistant properties were investigated. Modified PAni was prepared via two different techniques, conventional and rapid mixing method, in the presence of phenyl phosphonic acid (PPA) as dopant. The different PAni-PPA powders thus prepared were dispersed in an epoxy resin and coated on mild steel samples by drawing method. Tremendous improvement in hydrophobicity of the PAni-PPA (rapid)/epoxy was observed as compared to epoxy resin containing PAni-PPA (conventional method). The anticorrosion properties of these coatings on mild steel in 3 wt% NaCl were investigated using different electrochemical methods. Initial redox reactions and changes in conductivity of coating were reflected in the variations of open circuit potential (OCP). Both the coatings displayed stable high OCP, maintained their oxidative state, and provided corrosion protection for mild steel for more than 30 days. PAni-PPA (rapid)/epoxy gave better corrosion protection and showed higher ennoblement which may be due to the small particle size of PAni-PPA (rapid) leading to homogeneous mixing and better dispersion in the epoxy resin. Moreover, this coating is more hydrophobic in nature which is added advantage in case of corrosion-resistant coatings. The present investigation deals with preparation of highly (near super) hydrophobic coating containing conducting polymers for anticorrosion applications.

This paper describes casting-based microfabrication of metal microstructures and nanostructures. The metal was cast into flexible silicone molds which were themselves cast from microfabricated silicon templates. Microcasting is demonstrated in two metal alloys of melting temperature 70 • C or 138 • C. Many structures were successfully cast into the metal with excellent replication fidelity, including ridges with periodicity 400 nm and holes or pillars with diameter in the range 10–100 μm and aspect ratio up to 2:1. The flexibility of the silicone mold permits casting of curved surfaces, which we demonstrate by fabricating a cylindrical metal roller of diameter 8 mm covered with microstructures. The metal microstructures can be in turn used as a reusable molding tool. (Some figures in this article are in colour only in the electronic version)

This paper presents measurements and models for how the macroscopic curvature of microstructured polymers affects hydrophobicity. Flexible polymer substrates were fabricated with arrays of regular microstructures. The interaction of liquid drops with these surfaces was analyzed for flat substrates and substrates flexed into either positive or negative cylindrical shapes. Liquid droplet static contact angle and dynamic slide angle were measured for a range of surfaces. An increase in substrate curvature corresponded with decreased slide angle for liquid droplets suspended on the surface asperities. This phenomenon is investigated in terms of solid–liquid contact line and the periodicity of surface microstructures. We present a model that can be used to understand the observed phenomena and to design microstructure geometries for hydrophobicity. (Some figures in this article are in colour only in the electronic version)

In the development of anti/de-icing systems for aeronautics, wind turbines or telecommunication antennas to date, less attention is paid to coating strategies. The majority of studies dealing with coatings have focused mainly on reducing ice adhesion forces, to ...

The topography and wettability of the underside of English weed (Oxalis pes-caprae) leaves and of their biomimetic replicas are investigated. Polyvinyl siloxane molds were cast from the leaves and then filled with an epoxy pre-polymer to produce replicas. The particular topographical structures of leaves and replicas were evaluated by optical microscopy and Scanning Electron Microscopy (SEM) analysis. The static wettability of leaves and replicas was assessed by contact angle measurements, while the dynamic wettability was characterized by estimating contact angle hysteresis and studying the dynamic behavior of impacting water droplets. A smooth glass slip and its replica were used as control surfaces. The replica moulding method used was able to transfer the characteristic pattern of irregular 100 μm − 200 µm × 60 µm convex papillae interspersed with stomata of the original leaf to the epoxy replicas. The static contact angle of 143° ± 3° and the contact angle hysteresis of 2° indicate that the underside of the English weed leaf is close to superhydrophobic. The lower contact angles (130° ± 4°) and higher hysteresis (31°) observed for the replica when compared with the original leaves were associated to an inaccurate replication of the chemistry and structures of the three-dimensional wax projections covering the plant surface. Also, trichomes in the original leaves could not be accurately reproduced due to their flexibility and fragility. Differences in wetting behavior were also evident from droplet impact experiments, with rebound regimes prevailing in the original leaves and regimes characterized by higher adhesion and larger dissipation predominating in the replicas. Nevertheless, the morphological features of the leaf transferred to the replica were sufficient to promote a clear hydrophobic behavior of the replica when compared with the smooth epoxy reference surface.

The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nanocement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture is investigated. Experimental results demonstrate an increase in the compressive strength of mortars with SiO 2 nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer is proposed to facilitate the distribution of nano-SiO 2 particles. The application of effective superplasticizer and high-speed dispergation are found to be very effective dispersion techniques that improve the strength of superplasticized portland cement mortars, reaching up to 63.9 MPa and 95.9 MPa after aging during 1 and 28 days, respectively. These values compare favorably with the observed compressive strengths of reference portland cement mortars of 53.3 MPa and 86.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain the composite materials with improved performance.

We describe a simple method for fabricating superhydrophobic high temperature vulcanized (HTV) silicone rubber surfaces by direct replication using a compression molding system. The resulting rubber samples possessed micro-nanostructures on the surface. This micro- and nano-scale roughness produced a water contact angle of >160º and a contact angle hysteresis of <3º. The roughness patterns on chemically etched aluminum surfaces, which served as templates, were successfully replicated on the rubber surfaces. An antistiction coating applied to the template surface ensured that the rubber was completely removed during demolding and that the replicated micro-nanostructures on the silicone surface were preserved. Surface roughness of the aluminum templates was optimized at HCl concentrations of 15 wt. %, with a lower roughness value observed at acid concentrations above and below this value. The developed HTV silicone rubber surfaces also demonstrated a freezing delay and a self-cleaning capacity.

Superhydrophobic surfaces were obtained by superposition of microstructure—defined by replication of laser micromachined masters, with nanostructure—created by durable epoxy/γ-Al2O3nanoparticle composite, used for replication. Hierarchical surface topography thus obtained consisted of hexagonally spaced microcavities and nanoparticle agglomerates, exposed on the replica surface by radio frequency (RF) air plasma etching. Surface topography was further enhanced by rims around the microcavity edges, resulting from nanosecond laser micromachining defects in aluminum masters. Subsequent wet chemical hydrophobization with 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (PFTDTES) provided superhydrophobic behavior in replicas with a microcavity spacing of 30 μm, as indicated by a water contact angle of 160° and a sliding angle of 8°. The preparation method is relatively simple, inexpensive, and potentially scalable.

The reported research examines the effect of 5–70 nm SiO2 nanoparticles on the mechani-cal properties of nanocement materials. The strength development of portland cement with nano-SiO2 and superplasticizing admixture is investigated. Experimental results demonstrate an in-crease in the compressive strength of mortars with SiO2nanoparticles. The distribution of nano-SiO2 particles within the cement paste plays an essential role and governs the overall perfor-mance of these products. Therefore, the addition of a superplasticizer is proposed to facilitate the distribution of nano-SiO2 particles. The application of effective superplasticizer and high-speed dispergation are found to be very effective dispersion techniques that improve the strength of su-perplasticized portland cement mortars, reaching up to 63.9 MPa and 95.9 MPa after aging dur-ing 1 and 28 days, respectively. These values compare favorably with the observed compressive strengths of reference portland cement mortars of ...

Ice on surfaces can have dramatic consequences for human activities. Over the last decades, the design of new materials with anti-icing properties has generated significant research efforts for the prevention of ice accretion. Here we investigate water freezing temperatures on untreated and negatively charged hydrophobic stainless steel surfaces and use these temperatures to evaluate icephobicity. Supercooled water microdroplets are deposited and undergo a slow controlled cooling until spontaneous freezing occurs. Textured hydrophobic stainless steel surfaces functionalized with anionic polyelectrolytes brushes display unexpectedly lower freezing temperatures, at least 7 °C lower than polished untreated steel. On the basis of the entropy reduction of the crystalline phase near a charged solid surface, we used a modification of the classical heterogeneous nucleation theory to explain the observed freezing temperatures lessening. Our results could help the design of new composite materials that more efficiently prevent ice formation.