Preparation of superhydrophobic silver nano coatings with feather-like structures by electroless galvanic deposition

Abstract

Superhydrophobic silver nanocoatings with feather-like morphology are fabricated on copper substrates by electroless galvanic deposition. The coating exhibit superhydrophobicity with a contact angle of 156.4° and glide angle of 4° without any further surface modification. Scanning electron microscope (SEM), X-ray diffraction (XRD) and contact angle measurements are used to investigate the morphology, crystal structure and superhydrophobicity, respectively, of the coatings. The coatings exhibit high thermal stability; their water contact angle did not change when the coatings were heated to 200°C for 2 h. The mechanism of superhydrophobicity of the silver coating is discussed based on the work of Amirfazli, Wenzel and Cassie. The wettability of a solid surface is a very important interfacial behavior. Recently, superhydrophobic surfaces have attracted great interest because of their potential for application in the fields of water repellency, antisticking, self-cleaning and antifouling [1][2][3][4][5][6][7][8]. Wettability is normally characterized by measurement of the contact angle (CA) of a surface. Generally, surfaces with water contact angles larger than 150° and slide angles lower than 10° are called superhydrophobic [9,10]. In nature, many plants and insects have evolved to exhibit perfect superhydrophobicity; for example, the lotus leaf [7,11], water-strider legs [12], the hind wings of the waterman [13], cicadae [14], termite wings and backs of beetles [15,16]. Research has revealed that the dual-scale hierarchical structures of natural surfaces can not only ensure practical superhydrophobic performance but also provide mechanical durability [17]. Inspired by the fascinating functions of such structures in nature [18,19], two kinds of approaches have been proposed to artificially fabricate superhydrophobic surfaces. One is to create micro-/nanostructures on hydrophobic surfaces. Many techniques have been developed to generate rough solid surfaces, including crystallization control [20], phase separation [21,22], template synthesis [23,24], electrochemical deposition [25], and chemical vapor deposition [26]. The other approach is to chemically modify micro-/nanostructured surfaces with materials with low surface free energy [7]. Such materials include fluoroalkylsilane [27], fluoropolymers [28], organic polymers [29], and alkylketene dimers [30]. However, most of the techniques described above require multiple steps, specific substrates, special equipment or harsh chemical treatment, which seriously hinder the practical application of superhydrophobic materials. In this paper, we present a simple method to fabricate large-area superhydrophobic silver coatings on unmodified copper substrate. The structure and superhydrophobicity of the silver coating can be controlled simply by adjusting the initial concentration of silver nitrate and reaction time.

Silver-Modified η-Al2O3 Catalyst for DME Production

“…As the 10% Ag/η-Al2O3 catalyst was stable in the time on stream test over a period of 60 h, this suggests that presence of Ag enhance the surface hydrophobicity of alumina regardless of its oxidation state whether it was (0) or (+1). Moreover, it was reported that Ag (0) can promote the surface hydrophobicity 18 .…”

“…Catalyst 10% Ag/η-Al 2 O 3 showed a good pellet particle size a Total acidity = A × 10, 20 measured by TPD-Pyridine. b Acid density = B × 10, 18 , measured by TPD-Pyridine. distribution where at low loading (1 wt %) Ag is hardly distinguished over the surface of the catalyst and at the highest loading (15 wt %) Ag formed a separated island with big clusters that can be confirmed using the ETD detector as seen in Figure S2.…”

“… a Total acidity = A × 10, measured by TPD-Pyridine. b Acid density = B × 10,, measured by TPD-Pyridine. …”

“…Several techniques can be employed for this purpose; for instance, Zhao et al 17 used the electrodeposition of silver aggregate to prepare superhydrophobic surfaces with a water contact angle (CA) of 154°. An electroless galvanic deposition method was used by Feng et al 18 to fabricate superhydrophobic Ag nanocoatings with a CA of 156.4°, where the coatings showed a high thermal stability; the CA did not change with heating up to 200 °C for 2 h. Li et al 19 prepared a superhydrophobic coating of silver-doped titania@polycarbonate with a CA > 160°. Wu et al 20 demonstrated a convenient solution dipping method to make self-healing superhydrophobic materials using Ag nanoparticles prepared from silver nitrate solution with a CA of 159°.…”