Abstract
The alterations of wettability on metallic nickel surface by sub-nanosecond laser (1 ns, 1064 nm) induced surface modification was investigated. An approximate linear relation between surface contact angles (CAs) and accumulated fluence was established, which shows that with proper combinations of laser parameters, CA would reduce significantly from its initial value (∼96°) to approximately 3.1°. The microscopic inspection and roughness test reveal that the surface roughness on irradiated areas would increase remarkably due to the distribution of micro/nanoparticels and cracks that induced by laser ablation, which consequently improve the hydrophilic performance effectively. On the other hand, elemental analyses by use of XPS demonstrate that the nickel dioxides and nickel hydroxides were generated as the main components covering the self-organized structures. Such increasement in oxygen content, especially the growth of NiO and hydroxyl group provides a prerequisite in the transformation of nickel from initial hydrophobicity to hydrophilicity. And the integrated effects of surface morphology, roughness and chemistry ultimately led to the formation of super-wettability. The investigation indicates that, the sub-nanosecond laser is an effective tool to transform the metallic nickel into functional material with a highly hydrophilic surface by creating controllable topographical features and chemical properties on its surface.
Highlights
As an important property for solid surfaces, wettability is often used to evaluate the adhesion performance when a drop of liquid is in equilibrium on the surfaces.1 The wettability can typically be characterized by the apparent contact angles (CAs)
The scanning overlap shows a significant impact on the wettability modifications, in which higher overlap helps to accelerate the decline in contact angle (CA), i.e., in the condition of same pulse fluence, higher overlap shows a more hydrophilic tendency
In order to obtain the optimal hydrophilic performance, laser fluence of at least 8.0 J/cm2 is required for laser scanning overlap at 50% while only about 4.0 J/cm2 is necessary for the case of overlap at 75%
Summary
As an important property for solid surfaces, wettability is often used to evaluate the adhesion performance when a drop of liquid is in equilibrium on the surfaces. The wettability can typically be characterized by the apparent contact angles (CAs). With the inspiration of natural instances (for example, lotus leaves or mosses4), the concepts of superhydrophobic and superhydrophilic surfaces which yield CAs respectively larger than 150○ or smaller than 10○ are proposed.5–7 Such unique features especially the superhydrophobic property have attracted many interests of researchers and have been designed onto materials and applied in various scientific areas and human’s daily life, such as self-cleaning, water-repellency, anti-corrosion, adhesion modification, cooling enhancement, and biomaterials fabrication.. Chemical modification and physical roughening are two ways that intrinsically change the wettability of solid surfaces Based on these facts, various techniques/treatments such as sol-gel method, coating deposition, plasma treatment, chemical etching, and surface mechanical attrition have been used for controlling the wetting properties of the material surfaces. The key blemish and the localization presented in these methods, including poor flexibility, high-cost, time-consuming and even potential chemical hazard limit the further development of these techniques somewhat
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