Study On Construction And Wettability Of Micro-nanostructured Surfaces Based On TiO₂

Wettability is a very important property of solid surfaces and inspired by the superwetting phenomenon in nature,and the superwetting surface has been extensively studied.Since the discovery of photoinduced wettability switching of TiO₂ by Fujishima,much attention has been focused on smart surfaces with switchable wettability,because of their important application in intelligent devices,controllable oil-water separation and bioengineering.Although much research has been done about TiO₂-based surface wetting,some important and unclear problems remain to be solved.Therefore,in this paper,based on three different micro-nanostructured TiO₂-based surfaces prepared by different methods,three aspects were studied including underoil switchable wettability,oil and water separation process and restoration of superwetting switch,respectively and the correlative performances and mechanism were studied and analyzed in detail.At present,the research about wettability switching of TiO₂-based surfaces mainly focuses on water/oil wettability in air or underwater oil wettability swtiching.However,the research about water wettability switching in oil on TiO₂-based surfaces has been rarely reported.Firstly,in this paper,a series of TiO₂ nanotube arrays?TiO₂ NTAs?with different geometric parameters were prepared by combining anodic oxidation with heat treatment.By optimizing the oxidation time preparation parameter,the optimal oxidation time of TiO₂ NTAs was determined at120min under 40V constant voltage.Its morphology and crystal structure were further characterized,and then underoil water wettability switch process was systematically studied.Finally,the related mechanism was analyzed.The results show that the anatase TiO₂ NTAs can realize the reversible wettability switch from underoil superhydrophobicity to underoil superhydrophilicity by the alternation of UV irradiation and heat treatment,which can be ascribed to the cooperative effect between the surface nanostructures and chemical composition variation.Based on underoil reversible wettability switch of TiO₂ NTAs,some applications such as underoil droplet-based microreaction and water-removal from oil were demonstrated,respectively.In order to solve the problem of barrier layer caused by density difference of oil and water during oil and water separation process,a series of TiO₂ mesh film with micro-nanoporous structures were prepared by combining anodic oxidation with heat treatment.According to their separation performances,the oxidation time preparation parameter was optimized,and the optimal oxidation time of TiO₂ mesh film with micro-nanoporous structures was determined at 120min under 45V constant voltage.The morphology and crystal structure were further characterized,and the related separation performance and separation mechanism were detailedly investigated and analyzed,respectively.The results show that the prepared TiO₂mesh film has the special wettability with low adhesive underwater superoleophobicity and underoil superhydrophobicity.Based on the special wettability,it can realize highly efficient separation of light and heavy oil and water mixtures with separation efficiency higher than 99.2%.Besides,during the separation process,TiO₂ mesh film exhibits good corrosion resistance,cyclic separation stability,mechanical stability and special self-cleaning performances.In order to solve the problem that the microstructures on TiO₂-based surfaces are easily damaged under external force compression,leading to the loss of original superwetting switch.By combining TiO₂ nanoparticles with shape memory epoxy?SME?,nano-TiO₂ coated SME microarray surface was prepared by using template copying method together with ultrasonic treatment.By optimizing the ultrasonic time preparation parameter,the optimal ultrasonic preparation time was determined at 10min in TiO₂ nanoparticles/1,2-dichloroethane dispersion liquid.The morphology and composition of the prepared microarray surface were further characterized,and then the restoration performance of the superwetting switch on nano-TiO₂ coated SME microarray surface was studied in detail.Finally,its mechanism was analyzed.The results show that the prepared microarray surface can be converted from superhydrophobicity to superhydrophilicity by alternation of UV irradiation and dark storage,while the collapsed microarray surface under external force compression can only realize the wettability switch between hydrophobicity and hydrophilicity by the alternation of UV irradiation and dark storage.Based on the excellent shape memory performance of SME matrix material,the restoration performance of microarrays was endowed.Therefore,further heating the collapsed microarray surface,it can restore the initial state,and the microarray can regain UV-induced superwetting switch function,showing that the microarray surface has restoration performance of superwetting switch,which is mainly due to the cooperative effect between UV-induced TiO₂ surface composition variation and the restoration performance of microarray structures.