| Due to its surface properties, especially the presence of amine groups, plasma polymerized allylamine (PPAa) is involved in a large range of applications. Most of them are related to biology and biochemistry. As a biomedical material, its mechanical properties are extremely important, In this work, we aims to explore the the relationship between the structure and mechanical properties of PPAa films and the the stability of the films was also evaluated.In the present study, PPAa films on 316L medical stainless steel and Si(100) substrates were prepared by pulsed radio frequency (RF) plasma polymerization using allylamine as a precursor under different working pressures and bias voltages respectively. The effect of the working pressures and bias voltages on the composition, structure,surface morphology, wettability and mechanical property of PPAa films were investigated by step profiler, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscope (XPS), colorimetric staining with Acid OrangeⅡ, atom force microscope (AFM), contact angle measurement(CA), nanoscratch test and substrate straining method. The stability of the PPAa films in double deionised water using immersion tests was studied, and the day of water immersion was 1 to 30 days.The results of study as follows:In higher working pressure, the high particle concentrations and collision frequency in plasma led to the decrease of electron energy. As a result, the fragment reaction by bombarding on the monomer chain was weakened, and the amine groups could be retained highly in the structure which was proved by FTIR, XPS and colorimetric staining with Acid OrangeⅡ. AFM result showed that film prepared under the highest working pressure was smoothest. Contact angle test result indicated that the wettability increased as the working pressure increased. Scratch test and substrate straining test demonstrated that the cohesion between films and substrate decreased with working pressure increasing, and films made under low working pressure had better scratch resistance. Nanoindentation test revealed that the lowest of the hardness of the PPAa films was obtained under 15 Pa, which may was related to the content of the nirtrogen, C=N, C=N,C-C and some other factors.The FTIR spectra of PPAA fabricated under the different bias voltages had no obvious difference. The bias voltage can decrease the surface roughness. Mechanical test demonstrated that the influence of the bias voltage on the hardness, Young's modulus and the cohesion between films and substrate were non-linear but jumpy. When the bias voltage was-80V, the biggest hardness and Young's modulus of PPAa films were obtained, while the critical load was about 57.46mN, and the cohesion between films and substrate was the worst. When the bias voltage was-60V, the cohesion between films and substrate was the best and the critical load was about 61.37mN although it had the least hardness. The changes about mechanical properties were mainly related to the composition and structure of the PPAa films, especially the content of the sp C≡N and sp3 C-N.Stability test have proved that upon immersion, the contact angle were firstly increased and then decreased.The hydrophility of the PPAa film after 30 days immersing was larger than that of the fresh film. Scanning electron microscope (SEM) test have shown that there were bubbles and protrusions, the protrusions became weak (week 2) with further immersing and finally disappeared after 30 days. FTIR revealed the band of C-O, C=O and O-H groups emerged and the content of amine were decreased. There was a decrease in the nitrogen concentration and an oxidation of the films. The degradation of the film probably resulted from water penetration and subsequent change in the chemical composition and microstructure of PPAa film.This study showed that the change of working pressure and bias voltage played a significant role in the composition, structure and mechanical properties of PPAa films. The cohesion between films and substrate was optimized as the duty cycle 10/30, deposition time 60min, working pressure 15Pa, bias voltage-60V and the cohesion between films and substrate was 61.73mN. We will develop futher optimization to obtain ideal PPAa film.
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