Full length articleSuperhydrophobic properties induced by sol-gel routes on copper surfaces
Graphical abstract
Introduction
Superhydrophobicity is a property of surfaces displaying enhanced repellence to water, as expressed by large static water contact angles (WCA ≥ 150°) and small contact angle hysteresis (CAH < 10°). The discovery of a great number of natural superhydrophobic surfaces (SHS), working according to different mechanisms, has inspired scientists to produce artificial SHS mimicking their physicochemical features [1], [2], [3]. Synthetic SHS have proved to trigger great advantages in many applications because of the relevance of the induced properties, e.g. self-cleaning [4], prevention of icing phenomena [5], drag reduction [6], anti-fouling [7], and anti-corrosion [8].
Copper and Cu-based alloys are widely used in energy conversion devices (HVAC systems, vehicular coolers and radiators, heat sinks for electronic equipment cooling, etc.), which are often employed in corrosive environments [8], [9], [10]. Controlling Cu wettability is a key issue in such applications. So far, two main approaches to modify copper wetting properties have been reported in the literature. One deals with the deposition of either a single or multiple functional layers directly on the metallic surface, while a second one requires preliminary heat or wet chemical treatments of copper surface in order to promote peculiar morphologies and chemical modifications, mainly connected to the formation of Cu oxides. Examples of the first case are copper SHS produced by chemical bath deposition (CBD) of multiple layers [11], [12], [13], [14], [15] or by deposition of self-assembled monolayers (SAM) [16], [17], as well as by electrodeposition [18], [19], [20] or by a treatment with a suspension of hydrophobic functionalized nanoparticles [21]. The second approach is the most commonly reported in the literature to obtain highly performing copper SHS. It generally involves a preliminary etching or, alternatively, wet or dry oxidation steps followed by deposition of low-surface energy compounds like silanes, fluoroalkylsilanes or long-chain organic acids [16], [22], [23]. Surface activation promotes the formation of Cu oxides/hydroxides, while deposition of organic layers lowers the wettability towards water.
Surface scientists frequently present novel SHS preparations or syntheses combining many approaches and strategies. The route suggested in the present work consists in the deposition on Cu of a nanostructured, chemically hybrid thin film made of a ceramic oxide (Al2O3) obtained by sol-gel, coupled with a fluoroalkylsilane (FAS) moiety. The application of sol-gel coatings to obtain copper SHS has not yet been investigated in depth. This process makes neither use of oxidizing or acidic chemical reagents (as instead required by the etching method), nor of severe or complex thermal treatments. All deposition processes are carried out via dip coating, a fast and simple technique that can be easily transferred to an industrial scale. In order to broaden the range of investigations, copper SHS were produced using either a water-based or an isopropanol-based sol. The characterization here reported of the coated surfaces in terms of chemical composition and morphology allowed for a deeper comprehension of the observed wetting behavior.
Section snippets
Preparation of the alumina sol
Alcohol-based Al2O3 sol (referred to as A) was prepared according to the literature [24]: aluminum-tri-sec-butoxide (Al(O-sec-Bu)3, 97%, Sigma–Aldrich) was stirred in isopropyl alcohol (i-PrOH, 99%, Sigma–Aldrich) for 1 h at room temperature. Then, ethyl acetoacetate (EAcAc, >99%, Sigma–Aldrich) as the chelating agent was added and the solution was stirred for 3 h. Finally, water was gradually poured into the solution as a 1:1 V/V mixture with i-PrOH to promote hydrolysis of the alkoxide. The molar
Results and discussion
Wettability performance and surface morphologies of the coated surfaces are presented and commented, followed by ageing simulations and by XPS analysis.
Conclusions
A hybrid organic-inorganic coating was deposited on roughened Cu surfaces, which allowed to achieve high repellence against water. The inorganic component of coating consists of alumina nanoparticles obtained via sol-gel routes in two different media (isopropanol or water), deposited on the surface via dip coating and provided with a flower-like nanostructure resulting from immersion in boiling water. Such structure allows for the establishment of a Cassie-Baxter wetting state and the related
References (41)
- et al.
Bio-Inspired superoleophobic and smart materials: design, fabrication, and application
Prog. Mater. Sci.
(2013) - et al.
Superhydrophobic surfaces from natural to biomimetic to functional
J. Colloid Interface Sci.
(2011) - et al.
Current and emerging environmentally-friendly systems for fouling control in the marine environment
Biotechnol. Adv
(2013) - et al.
Study on fabrication of the superhydrophobic sol-gel films based on copper wafer and its anti-corrosive properties
Appl. Surf. Sci.
(2012) - et al.
Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process
Appl. Surf. Sci.
(2013) - et al.
Physical properties of nanocrystalline CuO thin films prepared by the SILAR method
Mater. Sci. Semicond. Process
(2013) - et al.
Chemically deposited copper oxide thin films: structural, optical and electrical characteristics
Appl. Surf. Sci.
(1999) - et al.
In situ synthesis and assembly of copper oxide nanocrystals on copper foil via a mild hydrothermal process
J. Mater. Chem.
(2006) - et al.
Growth of homogenous CuO nano-structured thin films by a simple solution method
J. Alloys Compd.
(2011) - et al.
Super-hydrophobic surfaces improve corrosion resistance of copper in seawater
Electrochim. Acta
(2007)
Monolayers and mixed-layers on copper towards corrosion protection
Electrochim. Acta
Green approach to fabrication of a super-hydrophobic film on copper and the consequent corrosion resistance
Corros. Sci.
Fabrication of biomimetic superhydrophobic surface with controlled adhesion by electrodeposition
Chem. Eng. J.
A versatile approach to produce superhydrophobic materials used for oil-water separation
J. Colloid Interface Sci.
Superhydrophobic fluoropolymer-modified copper surface via surface graft polymerisation for corrosion protection
Corros. Sci.
Wetting behavior and remarkable durability of amphiphobic aluminum alloys surfaces in a wide range of environmental conditions
Chem. Eng. J.
Improving the accuracy of determination of line energies by ESCA: chemical state plots for silicon-aluminum compounds
Appl. Surf. Sci.
Review of sol-gel thin film formation
J. Non-Crystall. Solids
Chemistry of alumina, reactions in aqueous solution and its application in water treatment
Adv. Colloid Interface Sci.
Boehmite nanopetals self assembled to form rosette-like nanostructures
Mater. Lett.
Cited by (35)
The effects of aging time on the sol-gel properties and its relationship with the anti-corrosive performance of coatings prepared by sol-gel dip coating
2023, Journal of Materials Research and TechnologyA facile and cost-effective fabrication of robust carbon black-based superhydrophobic coatings on aluminum alloy
2023, Surfaces and InterfacesIn situ fabrication of flower-like ZnO on aluminum alloy surface with superhydrophobicity
2022, Colloids and Surfaces A: Physicochemical and Engineering AspectsHeat exchangers for cooling supercritical carbon dioxide and heat transfer enhancement: A review and assessment
2021, Energy ReportsCitation Excerpt :Nano-coating is a new surface technique that has emerged since 2000’s. In the technique, a thin film of carbon nano tube (CNT) or other materials (Raimondo et al., 2017) is coated on a substrate to improve chemical or/and physical property of the substrate. Commonly, the film is subject to great micro surface area and superhydrophobic as well as large contact angle compared with the plain substrate.
Fabrication of superhydrophobic copper metal nanowire surfaces with high thermal conductivity
2021, Applied Surface ScienceCitation Excerpt :Chemical etching, a simple and cost-effective process, is often used to develop rough copper surfaces [4,13,16]. A sol–gel process is also used to form superhydrophobic surfaces using controlled microstructures on copper [3,15]. Such surfaces exhibit improved corrosion resistance and high mechanical stability.