Liquid Flow And Droplet Motion/Spreading In An Open Grooved Copper Channel With Gradient Wettability Inner Surface

The mainly research works are summarized as follows:First, gradient wettability surface with contact angle ranged from 89.1°to 23.6° was prepared on a rough copper open channel and plane by replacement technique. According to the principle of oxidation-reduction reactions, silver was replaced by copper from sliver nitrate aqueous solution and deposited on the copper substrate surface. In addition, ammonia was added into the sliver nitrate aqueous solution to control the reaction rate. The droplets spreading phenomenon on channel and plane with the same contact angle range was compared. It was found that the spreading velocity and distance of droplets within the grooved channel surpasssed on the plane. By Scanning Electron Microscopy(SEM) and X-ray Diffraction(XRD), surface microstructure and chemical composition were analyzed to explain the formation mechanism of gradient wettability surface.Secondly, gradient wettability surface(90.2°- 5.4°) amd uniform wettability surface(20.2°and 5.4°) were further prepared on the copper open channel via a facile alkali assistant oxidation technique. Liquid rise in the grooved channel by the gradient-driving force was discussed. A high-speed camera was used to record the liquid rising process. It was found that the smaller the diameter of the channel was, the higher and faster the water column would rise, and the groove surface with smaller contact angle could lead to the larger capillary force. The rising height was higher within the gradient wettability channels(90.2°- 5.4°) than the uniform wettability surface(20.2° or 5.4°). And the rising velocity was also faster within the gradient wettability channels than the uniform wettability surface. Scanning Electron Microscopy(SEM) and X-ray Diffraction(XRD) were employed to analyze the wettability, morphologies and crystal structure of the Cu(OH)2 nanoribbon arrays on copper substrate.Finally, gradient wettability surface was prepared on the copper substrate by electrochemical deposition technique. The contact angle ranged from 142.1° to 90.2°. The electrolyte was consisted of a mixed solution of anhydrous copper sulfate and concentrated sulfuric acid. And graphite wasthe anode electrode and copper with semicircularannular open channel was the cathode electrode. The droplets movement with volumnof 8μl, 5μl and 3μl on gradient wettability channels and plane were compared. It was found that the droplets could run uphill on the inclined surface(the inclination angle was 10°) driven by the gradient force. Besides, the moving velocity and distance of droplets within the gradient wetting channels surpasss on the same gradient planes. Scanning Slectron Microscopy(SEM) and X-ray Diffraction(XRD) were adopted to explain the formation mechanism of gradient wettability surface.