The Investigation On The Fabrication And Surface Properties Of NiTi Superhydrophobic Surface

Nitinol(Ni Ti),a common metal material for medicine,shows positive application prospects in the fields of surgical aids,orthopedic implants,and dental implants,etc.However,due to the instability of nickel oxide on surfaces,Ni Ti alloys might be prone to pitting corrosion over long-term usage,causing the leaching of Ni ions.It has been reported that excessive Ni ions can be harmful to the human body and induce diseases.Hence,a new method was proposed to fabricate superhydrophobic coatings on Ni Ti surfaces so as to enhance the corrosion resistance and reduce the release of Ni ions.The specific research contents and results are as follows:In consideration of the safety and non-toxicity needs for medical application,the hybrid of nanosecond laser ablation and PDMS modification was carried out to modify the wettability of Ni Ti surfaces,resulting in the superhydrophobic Ni Ti surfaces with low adhesion were successfully created.In order to reveal the mechanism of wettability transformation,the microscopic morphology,three-dimensional profile and chemical composition of Ni Ti samples were analyzed in detail via scanning electron microscopy,three-dimensional optical surface profilometer and X-ray photoelectron spectroscopy,respectively.It was found that Ni Ti surfaces formed the rough structure with the grid texture after laser ablation,which provided a structural basis for the superhydrophobic Ni Ti surfaces.In addition,the results of the chemical composition showed that the nonpolar functional groups contributed to the fabrication of superhydrophobic Ni Ti surfaces.The corrosion resistance of Ni Ti samples in simulated body fluid was evaluated by electrochemical corrosion tests,and the corrosion prevention mechanism of the surfaces with films(the laser-induced passivation films and the PMDS superhydrophobic coatings)was investigated.The results of potentiodynamic polarization curves,open circuit voltages and electrochemical impedance spectra indicated that both the film layers played a positive role in improving the corrosion resistance of Ni Ti alloys,and the superhydrophobic coatings had better corrosion resistance.In order to explore the influence of the superhydrophobic coatings on the release of Ni ions,an immersion experiment was conducted.The experimental results showed that the superhydrophobic coatings could significantly reduce the leaching of Ni ions from Ni Ti surfaces and improve the biocompatibility of Ni Ti alloys.A high-speed camera was utilized to record the interaction process between water droplets and Ni Ti surfaces during the impact process,and the effect of Weber number and surface wettability on the dynamic behavior of water droplets was further explored.The results indicated that as the Weber number increases,the maximum spreading diameter of the water droplet was larger,the minimum thickness of liquid film was smaller,and the spreading speed was faster.In addition,water droplets showed spreading and retraction behaviors on hydrophilic Ni Ti surfaces,while the bouncing behavior was additionally identified on superhydrophobic Ni Ti surfaces.It was also found that droplets alternated between compression-rebounding and stretch-rebounding behaviors during the bouncing process.The three-dimensional volume of fluid method was employed to simulate the process of a droplet impacting the superhydrophobic Ni Ti surface,whose feasibility was verified by experiments data.Based on the numerical simulation results,the relationship between droplet morphology and internal velocity/pressure distribution was studied in focus to reveal the evolution mechanism of droplet morphology during the impact process.