Study On The Wetting Properties Of Metal-doped Zinc Oxide Structured Surface And Its Application

Surface wettability is one of the important properties of solid interfaces,which is determined by surface microstructure and surface chemical components,and has a wide range of applications in the fields of anti-fog,anti-corrosion,self-cleaning,microfluidic chips,tunable optical lenses,biosensors and smart switches,etc.With the rapid development of technology,the multi-functionality and intelligence of surface wettability applications have become an urgent need.A large number of research results show that responsive wetting of solid surfaces is an effective way to achieve multifunctional and intelligent surface wettability.That is,the wettability of a solid surface is induced by external excitations（such as UV light,temperature,voltage,p H,and pressure,etc.）to be transformed.However,the reversible wetting transition technology is still immature and the wetting transition mechanism is still vague.Moreover,many new wetting phenomena are emerging,but the existing wetting theories are not sufficient to explain them.Although the applications related to solid surface wettability have been expanded to various aspects,multifunctionalization and intelligence are still weak.Therefore,it is necessary to continuously explore new technologies for the preparation of various structured surfaces and surface modification processes,and then discover new phenomena and new laws.It is also need to explore new materials as wetting substrates to study the multi-functionalization and intelligence of wetting properties,continuously expand related applications,and design and prepare multi-functionalized and intelligent wetting devices.Zinc oxide（Zn O）has a simple structure and an abundant elemental composition in the earth’s crust.Also it has wide band gap and excellent piezoelectric and photoelectric properties,and it is easy to introduce oxygen vacancies and perform elemental doping,which can not only realize the regulation of Zn O energy band structure,charge density and distribution,but also facilitate the study of electric and photovoltaic wetting,as well as the emergence of new phenomena and new laws through artificial regulation.Based on the above ideas,this dissertation is entitled"Structured surface wetting properties of metal-doped Zn O and its application",and the work is carried out in the following four aspects.（1）Reversible wetting transformation has gradually become an inevitable requirement for high level applications of solid wettable surfaces.We firstly prepared superhydrophobic Zn O@STA nanoarrays on Zn O substrate by hydrothermal method and introduced abundant oxygen vacancies simultaneously.Upon UV-visible light irradiation,the valence band electrons in Zn O were excited to form electron-hole pairs on the surface,which reacted with O₂ and H₂O in the adsorbed air on the surface to form hydrophilic radicals,thus inducing the transformation of Zn O@STA from a superhydrophobic to a superhydrophilic surface.The introduction of oxygen vacancy defects induces more electron-hole pairs to be excited by visible light,which can significantly enhance the wettability transition.In addition,further heating of the transformed superhydrophilic Zn O@STA surface leads to the dissociation of the photoinduced hydroxyl radicals from the Zn O@STA surface and the reduction of the phototropic superhydrophilic surface to the initial superhydrophobic surface.Moreover,increasing the heating temperature can accelerate the reverse wetting transition.Apparently,a stable and reversible transition between superhydrophobic and superhydrophilic on the surface of Zn O@STA nanorod arrays can be achieved after light and heating.（2）In order to expand the application of solid surface wettability,we developed a simple method to prepare conductive coatings by adding silver nitrate（Ag NO₃·6H₂O）to a precursor solution containing stearic acid（STA）with heating and stirring.Subsequently,Ag-Zn（OH）₂@STA composite coating was successfully prepared on the surface of cotton fabric by dip-coating method,which was mainly formed by encapsulating Ag nanoparticles of STA embedded in the mesh structure of Zn（OH）₂ nanosheets encapsulated with STA,and all Ag nanoparticles and Zn（OH）₂ nanosheets were bonded and co-adhered to the fabric surface by STA.Unique coating structure makes the fabric super hydrophobic and conductive,flexible for wearable devices.The coating conductivity decreases linearly as the bending angle of the coating increases,and has been successfully applied to highly sensitive sensors for monitoring the real-time bending of human joints,which has good prospects for emerging applications such as wearable electronic sensors,electronic skin and corrosion-resistant circuits.（3）Based on the second work,Ag-Zn（OH）₂@STA conductive coatings were successfully spin-coated on Zn substrates,and after heating and drying at 140°C,Zn（OH）₂ decomposed into Zn O,and Ag-Zn O@STA nanocomposite coatings with metal Ag doped Zn O were successfully prepared.The effects of silver concentration and surface microstructure on the performance of EWOD were deeply analyzed,and the introduction of silver nanoparticles not only improved the dielectric constant of the dielectric,but also reduced the response time of EWOD.This unique structure allows the EWOD to respond to contact angles ranging up to 100°and threshold response voltages below 1 V.Finally,the coating has good antibacterial properties and is very suitable for medical detection.Therefore,the contact angle（CA）is used as the response strategy of the sensor,and glucose concentration detection is successfully achieved,especially for low concentration glucose solution with high sensitivity.（4）Intelligence is an important requirement for modern device design and development,and memristors are an emerging artificial intelligence device.Therefore,Fe doped Zn O memristors were prepared by successfully doping the metallic element Fe into the Zn O nanocone array structure using a simple hydrothermal method,and the EWOD response of surface droplets was investigated in depth.The doping of Fe elements introduces a large number of oxygen vacancies in Zn O,and their trapping and untrapping of electrons induces a reversible electron-blocking behavior.Based on this property,intelligent control of surface water droplets is achieved,which is very beneficial for the development of artificially intelligent microfluidic devices.