| Wettability is a special and important property of solid surface.Inspired by the phenomenon that lotus leaves emerge from silt without being stained,people gradually extend their research attention to the wettability field.As an important branch in the wettability field,the unique gradient wettability has great significance in the construction of controllable wettability surface.Wettability gradient surface is a special gradient surface that along the direction parallel to the solid surface,one or more surface properties(surface topography,thickness,surface chemical composition,etc.)have a continuous change with the change of position and thus cause the continuous change of surface wettability.The infiltrating gradient surface has important application value in realizing droplet self-transport,studying cell adsorption kinetics and improving heat exchange efficiency.In this paper,the simple and practical method of ammonia-alkali oxidation is adopted.Taking the copper mesh as the experimental material,the continuous change of reaction time on the surface of the copper mesh can be achieved by slowly dropping ammonia-alkali mixture solution with the separation funnel,and the continuous wettability gradient copper mesh from superhydrophilic to hydrophobic can be obtained.The experimental principle is that when the copper mesh and ammonia alkali mixture solution contact and react,a kind of copper hydroxide nanowire will grow on the surface of the copper mesh,the growth of the nanowire increases the surface roughness,at the same time,due to the presence of hydroxyl hydrophilic groups on the nanowire,the surface of the copper mesh shows hydrophilicity or superhydrophilicity.After a series of characterization and analysis of the wettability gradient copper mesh,the causes and influencing factors of the wettability gradient were discussed in detail.First by scanning electron microscope observation on the surface of the bronze microstructure,analysis of the nanowire growth status and the relationship between reaction time,the results show that according to the different reaction time,the growth of nanowires situation also happen some change,with the increase of reaction time,the distribution density and growth of nanowires length will also increase gradually,the continuity of the nanowires growth change is a change in the surface of the bronze invasive presents gradient key factor.Then contact Angle measurement instrument are used to observe and measure the continuity of the copper wire surface contact Angle,can be very intuitive see along the direction from long to short reaction time,contact Angle from 3 °(superhydrophilic)gradually increased to the original contact Angle is 98.6 °(hydrophobic),confirmed the feasibility of the experiment scheme.Then the twoexperimental conditions,concentration of mixed solution and droplet acceleration,were changed respectively.The results show that the concentration of the solution also affects the growth of nanowires on the surface of the copper mesh.At high concentration,the nanowires grow faster,and the contact Angle has reached hydrophilicity at the initial stage of reaction,so the nanowires cannot present an ideal gradient change.With the decrease of the concentration,the growth rate of the nanowire decreases,and the change of the contact Angle is also obvious,so the ideal gradient change can be obtained by selecting the appropriate concentration.The droplet acceleration affects the length range of the gradient.In the same reaction time,the faster the flow rate is,the larger the area of copper mesh reacting with the solution will be,and the longer the length of the wetting gradient will be.Therefore,the gradient change length required for practical application can be obtained by controlling the droplet acceleration of the solution.Finally,for the difficult oil spill event in the sea,we studied the movement state of oil droplets on the surface of the inclined wetting gradient copper net.Meanwhile,a single superhydrophilic copper mesh was used as the control experiment.The results show that the oil droplets roll rapidly on the surface of a single super hydrophilic copper mesh and eventually fall off the copper mesh,while the oil droplets move differently on the surface of the wetting gradient copper mesh.Oil droplets in the hydrophilic section and the superhydrophilic section can freely roll,but in the hydrophobic section can not roll,but will adhere to the surface of the copper mesh.Through the analysis,it was found that water could not completely infiltrate the micro-nano structure of the hydrophobic section of the copper mesh,and the residual air in the structure would have a adhesion force on the oil droplets,which hindered the free movement of the oil droplets.According to this special phenomenon,we simulated the sea overflow oil processing process,the experimental results show that the invasive gradient copper network can efficiently and the implementation of the oil-water separation in a row,and has strong resistance to strong alkali and high temperature resistant,proved that the invasive gradient copper network in large-scale cross-flow oil-water separation of important value in the field of application.After that,the behavior of underwater bubbles on the surface of the copper mesh was studied,and a simple water electrolysis experiment proved that the infiltrating gradient copper mesh could improve bubble precipitation and electrolysis efficiency,and it had a great application prospect in gas evolution reaction. |
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