Preparation Of ZnOHF Films With Controllable Wettability And Its Application On Liquid Transportation And Oil-water Separation

In recent years,the research on the preparation and properties of ZnOHF(Zinc Hydroxyfluoride)has been extensive,but the research on its wettability is few.ZnOHF can change its surface wettability through light induction.Due to the diverse morphology of ZnOHF,it is possible for ZnOHF to serve as an intelligent material with controllable wettability.In this thesis,based on the growth of ZnOHF branched structure films on nickel mesh,the surface wettability of ZnOHF branched structure was controlled by the combination of ultraviolet light and deposition of monolayers.The three films with horizontal gradient wettability,vertical gradient wettability and superhydrophobic/superhydrophobic properties were prepared.The application of these special wettability surfaces in liquid transportation and separation was further researched.ZnOHF films were grown on a nickel mesh surface by a hydrothermal method.The films have micro/nano flower-like branching structures,and superhydrophilicsuperhydrophobic reversible and repeatable wettability conversion property.The water contact angle of ZnOHF film is 0 ° in its initial state,which can be increased to 152 °after dark room treatment for 5 d(5 days)or 150 °C heating treatment for 6 h,and can restore the film to superhydrophilic state after flowwing UV irradiation.Based on the morphology of ZnOHF at different reaction time and the existing relevant growth mechanism,it was believed that the flower-like branch structure of ZnOHF might be produced by crystal splitting.For ZnOHF films with horizontal gradient wettability,the spreading of water droplets on the uniform surface and the gradient surface was researched.It was found that the gradient surface can spread directionally,and the spreading speed(7.42 mm/s)is greater than that of the uniform surface(1.16 mm/s).The gradient surface can still make the water droplets spread rapidly(3.84 mm/s)when inclined at 30 °.The influence factors of droplet spreading distance and spreading speed,such as droplet volume and surface wettability gradient,were further studied.It was shown that the main driving force of droplet directional spreading was unbalanced surface tension.ZnOHF films with bilateral gradient could make the droplets transport from the hydrophobic zone on both sides to the hydrophilic zone in the middle.Then the water droplets gathered in the middle,and finally penetrated the films.Therefore,the water was collected in a bottle.The amount of water collection was 31% higher than the original surface.In the study of ZnOHF films with vertical gradient wettability,it was found that the surface tension difference in the thickness(vertical)direction of ZnOHF film was obtained,because the water contact angles of the front(light illumination region)and back(backlight rigion)sides of ZnOHF film were different after illumination with the same time.When the ultraviolet light is irradiated for 2～4 h,the surface tension difference was between 67.14 and 17.5 m N/m,the water droplet on the vertical gradient wettability ZnOHF film can directly transport from top to bottom in air.When the ultraviolet light was irradiated for 2～3 h,their surface tension difference was enough to make the water droplet directional transport from bottom to top(with antigravity).It was found that the water droples on a vertical gradient wettability ZnOHF film can also be directional transported at the oil-water interface.For superhydrophobic/superoleophilic ZnOHF films,the effects of static/dynamic wettability and silane chain length on wettability and oil-water separation performance were studied.The results show that the water contact angle of super hydrophobic/superoleophilic ZnOHF film is as high as 158 °,and has a small rolling angle and adhesion;The contact angle of oil droplets is 0 °,and its permeability is good.After silane deposition,the water contact angle of ZnOHF films increases with the increase of carbon chain length,but the change range is small(the contact angle changes from 145 ° to 158 °).The oil-water separation efficiency is higher with the carbon chain longer.The super hydrophobic/ superoleophilic ZnOHF films have an oil-water good separation efficiency(above 93%),and a good reusability.