Fabrication Of Bifunctional Thin Films With Unusual Wettability On Copper Substrate

Wettability is an important property of solid surfaces that is governed by both the chemical composition and the surface geometrical structure. In recent years, bifunctional interfacial materials with unusual wettability such as superhydrophobicity/superoleophilicity, superhydrophobicity/superoleophobicity and superhydrophilicity/superoleophilicity have attracted significant interest for their potential and practical applications in everyday life, industrial and agricultural production and fundamental research. For example, superhydrophobic and superoleophilic surfaces of filters can separate oil and water mixture easily and efficiently, which paved a novel pathway for the development of modern separation techniques, superhydrophobic and superoleophobic surfaces of textiles have self-cleaning properties by means of repelling oils and water, and superhydrophilic and superoleophilic surfaces of windshield glasses can keep transparent and clean when liquids contact on the windshield. As a result, it still remains a great challenge to construct the surfaces with high stability and unusual wettability using simple and convenient techniques.Compared to other approaches, galvanic ion exchange reaction is simple, time-saving, inexpensive, and easier in operation at lower temperatures. It has been used extensively for the formation of nanostructural surfaces by simply making use of the galvanic ion exchange reaction between a substrate and ions, and then to produce superhydrophobic surfaces after modified by low surface energy materials.In this paper, the silver films with different micro/nanobinary structure were facilely fabricated on copper substrates by using galvanic exchange reaction, and after being modified by self-assembled monolayer of different long-chain fatty acid such as12-hydroxy stearic acid, lauric acid or perfluorooctanoic acid, the as-prepared substrate showed tunable and unusual wettability. The main results are showed as follows:1. Homogeneous and dense dendrite micro/nanostructural silver coating was prepared by immersing copper substrate in silver nitrate solution through galvanic exchange reaction.12-hydroxy stearic acid or lauric acid modification to the coating resulted in a formation of superhydrophobic/superoleophilic surface. Whereas perfluorooctanoic acid passivation brought about a superhydrophobic/oleophobic surface. And the relationship between coating time and water contact angles were also discussed.2. The superhydrophobic and high-oleophobic flower-like silver films with micro/nanobinary structure were facilely fabricated on copper substrates in a one-step process via galvanic exchange reaction, by simply immersing the copper substrates in silver nitrate solution containing perfluorooctanoic acid in different quantities. And the relationship between surface wettability and the concentration of perfluorooctanoic acid and reaction time were also studied.3. The dendrite silver films with micro/nanobinary structure were facilely and easily fabricated on copper substrates by simply immersing the copper substrates in the mixed solution of silver nitrate and nitric acid for a short time using galvanic exchange reaction. And after being modified by a self-assembled monolayer of12-hydroxy stearic acid or lauric acid, the as-prepared substrate indicated both superhydrophobic and superoleophilic properties simultaneously. We also studied the concentration of nitric acid in the mixed solution and the reaction time that effect on the surface wettability.The superhydrophobic surfaces fabricated in this paper showed good chemical stability in water and some common organic solvents such as ethanol, acetone and hexane and durability at ambient conditions.