Study Of The Wetting Control In Oil On Nanostructured TiO₂ Film

In the past few years,smart superwetting materials become a new research focus.These smart materials can be used in a wide range of applications including controllable oil/water separation,microfluidic devices,no-loss droplet transportation,etc.,duetotheirspecialswitchablewettingtransitionssuchas superhydrophobicity/superhydrophilicity transition,and high/low adhesions transition,under external stimulus.Up so far,lots of such materials have been prepared by modifying responsive molecules onto the rough micro/nanostructures,however,most of these works are focused on the transition in air condition,in complex environment,such as oil condition,related researches are still extremely rare.Herein,nanostructured TiO₂ films were prepared,and based on the light-responsivity of theTiO₂,smart wetting control in oil can be realized.The main content is as follows:By a simple pulling technology,TiO₂ nanoparticles can be coated evenly onto a glass substrate,and a nanostructured film composed by TiO₂ nanoparticles can be obtained.The results indicate that the obtained film is superhydrophobic in oil,under the irradiation of UV for a certain time,the film becomes underoil superhydrophilic,after a further heating process,the film would restore its original state,that is,the underoil superhydrophobicity can be observed again.Meanwhile,such a reversible transition can be repeated several times,demonstrating a good stability of our film.The smart wetting performance can be ascribed to the synergistic effect between the nanostructure and the chemical composition variation on TiO₂ nanoparticles under the UV irradiation and heating treatment.Through a simple electrodeposition process,arrays of TiO₂ nanotubes can be prepared on a flat titanium substrate.When the as-prepared film is put into oil,a water droplet can stand on the film like a sphere,and meanwhile,it can roll easily with an extremely low sliding angle,indicating that the as-prepared film is low adhesive superhydrophobic in oil.After the UV irradiation for about 10 min,a similar water droplet can still stand on the film like a sphere,however,it cannot sliding and be pinned on the film firmly,meaning that the film becomes high adhesive even though it still shows the superhydrophobicity in oil.Further heating the film,it can be seen that the film returns to the initial state,and low adhesive rolling performance can be observed again.Meanwhile,such a smart transition can be repeatedly several times.The mechanism analysis indicates that the smart controllable adhesion on the film is ascribed to the combined effect between the surface nanostructure and the chemical composition variation for TiO₂ nanotubes.