Preparation And Characterization Of Gradient Wettability Surface On Copper Substrate

As one of the most important properties of solid surface, wettability is mainly determined by the combined action of surface chemical composition and microstructure. Recent years, as gradient wettability surface has important application value in various area such as droplet moving and microfluidics fabrication, researchers pay great attention to the preparation technology, formation mechanism and functional surface of gradient wettability surface. Copper is a common metal material in industry and daily life, so fabricating gradient wettability surface on copper substrate is of great application value. The mainly research works are summarized as follows:First of all, gradient wettability surface was prepared on a rough copper substrate after electrochemical anodic oxidation and dehydration by self-assembly technique. It was based on the control of chemical modification time in palmitic acid ethanol solution or dodecanethiol ethanol solution, the gradient wettability surface changing from13.9°to130.6°and from19.7°to141.2°were prepared. The influence of concentration and adding speed of palmitic acid ethanol solution and dodecanethiol ethanol solution on the wettability of copper substrate were discussed. By analyzing the formation mechanism, we found that the gradient wettability surface was formed by the joint action of amplification effect of rough surface and self-assembled monolayer of palmitic acid or dodecanethiol.Secondly, gradient wettability surface was prepared on the copper substrate by electrochemical anodic oxidation technique. It was based on varying anodization time of different positions along the substrate surface in an aqueous solution of KOH. The surface gradient wettability changing from90.4°to4.2°was prepared. The effects of constant current intensity, KOH aqueous solution concentration and temperature on the contact angles evolution were studied. It was found that the formation of gradient wettability surface is closely related to surface chemical composition and surface rough microstructure by the means of Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).Gradient wettability surface was further prepared on the copper substrate via a facile alkali assistant surface oxidation technique. It was based on the control of cupric hydroxide (Cu(OH)2) nanoribbon arrays growth from the upper part to lower part along the vertically placed copper substrate in an aqueous solution of NaOH and (NH4)2S2O8. Thus the gradient wettability functionalized Cu(OH)2nanoribbon arrays were directly fabricated on the copper substrate by varying the immersing time of different positions along the substrate surface, the surface gradient wettability changing from the original contact angle of copper substrate (90.5°) to surperhydrophilicity(3.0°) was prepared. The surface fabricated on the copper substrate may keep its gradient wetting property after immersed in a water bath at100℃for10h. The water contact angle measurement (CA), Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the wettability, morphologies, crystal structure, and surface chemical compositions of the Cu(OH)2nanoribbon arrays on copper substrate.Finally, gradient wettability surface was prepared on the copper substrate via chemical deposition technique. It was based on the control of elemental silver growth from the upper part to lower part along the vertically placed copper substrate in an aqueous solution of AgNO3. The surface gradient wettability changing from90.7°to151.4°was fabricated on the copper substrate. The effect of AgNO3aqueous solution concentration on the contact angles evolution was studied. The wettability, morphologies, crystal structure were analyzed by the water contact angle measurement(CA), Scanning electron microscopy (SEM), X-ray diffraction (XRD) and3D surface topography. We found that the formation of gradient wettability surface was closely related to surface microstructure. The property of water resistant and thermal stability of the prepared gradient wettability surface were tested.