Researches On Microstructure Evolution And Wettability Regulation Of Diamond-like Film

Diamond-like carbon(DLC)film is a kind of metastable amorphous materials composed of sp~3 and sp~2 hybridized carbon atoms.It shares the excellent properties of diamond and graphite,such as high hardness,good optical properties and friction resistance.Surface wettability is one of important properties of DLC films.DLC films with special surface wettability,especially superhydrophobicity(water contact angle,WCA?150°),can meet the unique application requirements of different devices,such as anti-fouling and anti-corrosion for mechanical devices,waterproof,anti-fogging and anti-icing for optical devices,and anti-adhesion of blood and platelet for medical devices.However,DLC film surface is generally considered to be intrinsically hydrophilic(WCA<90°),and the surface roughness is very small.Consequently,it is difficult to endow the DLC film surface with superhydrophobicity that always occurs on a solid surface with intrinsic hydrophobicity and complex rough structures.Therefore,the preparation of superhydrophobic and self-cleaning DLC films will have a significant impact on future theoretical researches and practical applications.In this paper,DLC films with different structures were deposited on monocrystalline silicon substrates by magnetron sputtering technology.The effects of technological parameters on the microstructures and surface wettability of DLC films were systematically studied.After the optimization of film deposition conditions and substrate surface patterns,the surface wettability of the DLC films can be regulated in a wide range from hydrophilicity to superhydrophobicity.The main research works are as follows:1)DLC films with different microstructures were prepared on polished monocrystalline silicon substrates by using magnetron sputtering via controlling substrate temperature and sputtering power.The wettability of the films surfaces can be changed from high hydrophilicity(WCA,30°)to strong hydrophobicity(WCA,132°).Based on the microstructures characterizations and surface energy calculation,the influence of microstructure evolution of the DLC films on surface wettability was studied,and the mechanism of inherent wettability transition was revealed.2)The surface of monocrystalline silicon substrate was textured by chemical etching in a NaOH aqueous solution under different etching time.The results showed that,with increasing etching time,the size of micro-scaled pyramids on the silicon surface increases first and then decreases.When the corrosion time is 50 min,the pyramid size tends to be consistent and the distribution is relatively uniform.3)Based on the bionics principle of lotus leaf effect,the intrinsically hydrophobic DLC film was deposited on the etched micro-structured monocrystalline silicon substrates to prepare artificial superhydrophobic surfaces.The results showed that all the films were hydrophobic,and the maximum WCA was as high as 157°.The static and dynamic wettability tests showed that the film surface had stable superhydrophobicity and self-cleaning ability.Based on the classical Wenzel and Cassie wetting theories,the effect of substrate textures change on surface wettability of the DLC films was analyzed.4)Through the water droplet impact test on DLC films,it was found that water droplets completely rebounded after impacting on the superhydrophobic DLC film surface at different velocities.But,the droplets oscillated or partially rebounded after impacting on the hydrophobic DLC film surface.It was thus concluded that the prepared superhydrophobic DLC film had good impact resistance.