Azobenzene-containing Superhydrophobic Silica Surface With Photoswitchable Wettability

In recent years, with the development of surface wettability, the requirement forthe preparing of superhydrophobic surface became higher and higher.Superhydrophobic surface with single property cannot satisfy the needs of people’lifeand industrial production. The fabrication of smart superhydrophobic surfacematerials has become a key point in the research of surface wettability. Theorganic/inorganic nanoparticles with superior strength, abrasion resistance, attractedthe attention of many researchers, and can be used as a super hydrophobic materials.This experiment takes4-trifluoro methoxy aniline and silica as the startingmaterial,synthesized the azobenzene/silica nanoparticles through covalent grafting.As a consequent, we obtain a superhydrophobic surface, and the wettability canswitch between superhydrophobic and hydrophobic by the alternative with UV lightand Visible light. Another work bears on the preparation of azobenzene/silicacomposite with core-shell structure particles, and they can be used to fabricate asuperhydrophobic surface. The component and structure of these materials werecharacterized by Fourier transform infrated （FTIR） spectroscopy, thermogravimetricanalysis（TGA）, uv-vis absorption apparatus, Contact Angle tester, H1-NMRspectrometer, Field emission scanning electron microscope （FE-SEM）, Transmissionelectron microscopy （TEM）.（1） Preparation for Azobenzene/silica nanoparticles: the whole process includestwo steps: firstly, as raw materials,4-trifluoro methoxy aniline was used to synthesisalcohol hydroxyl azobenzene molecules. Then, fabrication of Azobenzene/silica wascarried out via covalent grafting alcohol hydroxyl azobenzene molecules on the silicasurface which was modification by toluene diisocyanate. The results of FTIR andTGA shows that the nanoparticles were obtained successfully. The surface fromAzobenzene/silica nanoparticles shows a high contact angle up to151.2±1.3owhichreached the super-hydrophobic effect. When we irradiated the surfaces with365nmUV light, the surfaces changed into hydrophobic effect with contact angle to110.2±2o.We concluded that these changes were due to the isomerization of the azobenzeneunits which were confirmed through the color changes and the electron microscopyfigures. Camparative with previous experiments, there were a lots of advantages:①The surface can switch water wettability through the alternative with UV irradiation or Visible irradiation.②The whole process of preparation was very simple and it waspotential for large-scale preparation.③The super-hydrophobic surfaces had greatweather resistance and can be storage for a long time. Finally, there were only smallchanges with the contact angle.（2） Preparation for PAzo/SiO₂composite microspheres: the whole processincluded two steps. firstly, coupling agent was used to modify SiO₂by sol-gel method;secondly, fabrication of PAzo/SiO₂dispersions was carried out via in-situ free-radicalpolymerization strategy. From the SEM images, the MPS-SiO₂gel particles withaverage diameter of300nm exhibited regular spherical shape and obviousaggregation. Compared with the MPS-SiO₂particles, the resulting PAzo/SiO₂particulates showed spherical shape and bigger size. From the TEM images, it can befound that the dispersed particles have a distinct layer of PAzo chains grafted onto thesurface of the silica. Compared with MPS-functioned particles, the surface of thePAzo/SiO₂microspheres became rougher. By directly depositing the resultedPAzo/SiO₂microspheres onto the glass slide, the surface showed super-hydrophobicproperty with the contact angle （CA） up to150±1.2o.Our strategy possesses variousadvantages:①The PAzo/SiO₂composites present super-hydrophobic propertieswhich have many potential applications, such as micro-fluidics, pharmaceuticalchemistry, biochemistry and separation.②The whole reaction involves only twosteps, which makes the synthetic process more facile, therefore, it is possible tointroduce it into industry applications.③The as-prepared hybrids show excellentstability.