Preparation Of Super-hydrophobic TiO₂ Films By PECVD With A Help Of Pulsed Bias And Research The Wettability

In recent years,super-hydrophobic surfaces with water contact angel(CA) greater than 150°are arousing significant attention because they will bring great convenience in daily life as well as in many industrial processes.It is well-known that TiO₂ photocatalysts have strong oxidation under UV illumination,and various organic stains accumulated on TiO₂ films are oxidized finally into inorganic substance. Therefore self-cleaning films with both super-hydrophobic and photocatalysts have more meanings and have arose many researchers interest.Our work is tried to prepare super-hydrophobic TiO₂ films by plasma enhanced chemical vapor deposition.In this Paper,super-hydrophobic TiO₂ films with micro-and nano-composite structure were successfully prepared on glass substrate by plasma enhanced chemical vapor deposition(PECVD)from mixtures of tetraisopropyl orthotitanate(TIPT)and oxygen.Surface roughness,wettability,chemical composition,chemical structure, optical properties were studied in dependence on discharge power by means of scanning electron microscope(SEM),transmission electron microscope(TEM), atomic force microscope(AFM),Contact angle measurement(CAM),elemental analyzer(EA),inductively coupled plasma opticai emission spectrometers(ICP-OES), fourier transform infrared spectrometer(FTIR)and UV-Vis absorption spectrum.It is found that the film was composed of microsize coagulation of nanosize particles,and the microsize papillates were composed by nanosize grain.The films were composed with inorganic Ti-O_X and organic CH_X composition(with low surface energy),which was confirmed by FT-IR.Besides,the water contact angle of the films could be as high as 162°and increased with the discharge power.The roughness induced by the combination of micro/nano structure and the residues of organic CH_X groups are responsible for the observed super-hydrophobicity.The partly crystalized TiO₂ nanoparticles deduce UV absorption of the films.Besides,pulsed bias was used as assistant for deposition of TiO₂ films.A comparative study on plasma deposition with pulsed bias and without pulsed bias was made.The films prepared in plasma discharge without a pulsed bias have super-hydrophobicity,while the films prepared in plasma discharge with a help of pulsed bias do not have super-hydrophobicity.However,the films changed from hydrophobic to hydrophilic with the increase of pulsed bias,and reached super-hydrophilic when the pulsed bias is-800V.The films deposition without pulsed bias are with a large rough surface,the films with surface becomes smooth when deposited with pulsed bias as evidenced by SEM and AFM.Annealed the super-hydrophobic TiO₂ films in atmosphere at 500°C for one hour resulted in the change from amorphous to anatase as measured by XRD,also a change from super-hydrophobic to hydrophilic character.It is obviously that plasma enhanced chemical vapor deposition with pulsed bias is a wonderful measure to prepared super-hydrophobic and super-hydrophilic TiO₂ films.