Study On The Photooxidation Aging Of Parylene C Film

Abstract Parylene C (poly 2-chloro-para-xylylene, for short PC) film is a new protective coat material with excellent performance, and it is widely used to isolation safeguard in many fileds such as aviation, war industry, micro-electronics, semiconductor and so on. Aiming at the photooxidation aging characteristics of Parylene C film, the variations of its structure and performances under different aging surroundings were studied in this papar to obtain its environment adaptability.In this paper, two kinds of means, i.e. unaffected insolating and xenon lamp aging experiment box, were used in photooxidation accelerative ageing experiments for Parylene C films both new made and protected from light for one year. The appearance patterns and the changes of aggregate and chain structure after aging were characterized. The properties of thermology, mechanics and moisture-penetrability were studied. The geometry of the film was optimization computed with Gaussian 03W software package. The stability of oxidation construction, structure-performance relationship, and the photooxidation aging mechanism of Parylene C film were analyzed, and lastly an effective characterization method was established to indicate the variation information of its structure and performance.Through photooxidation aging tests, it is discovered that the samples exposed to open-air light filter after 168 hours have no obvious aging evidence, while color transition occurs after only 34 hours for the samples under exposure to space filter, which is similar to the results of unaffected insolation. Thus, the aging of the samples happens more easily with space filter than with open-air filter.After irradiation, the surface of Parylene C film exhibited yellowing phenomena with different degree, and the yellow index increased linearly. The AFM results showed that the degree of roughness of surface augmented whereas the thickness of the films had hardly variance.With DSC, XPS, IR, UV-VIS and PGC/MS analysis, the conclusion comes that the illumination made the crystals of Parylene C film more perfect; as the illumination kept on, photolysis took place, which resulted in the decrease of crystallinity and vitrification point. However, when the illumination reached to some extends, the hydrogen bond produced by the luminous energy and associated oxygen made the molecules partly cross link and the vitrification point increase. The illumination raised the degree of oxidation of the films' surface and even to saturation. The CH₂-CH₂ in the principal chains could be easily oxidized, producing oxidation aggregates such as -C=O and -COOH. The fragments of main oxidation product after decomposition first augmented with the increase of the aging time; then due to the partly cross linking, the fragments decreased rapidly.Meanwhile, the analysis through TG, DSC and nano-indentation showed that the oxidized Parylene C films had lower decomposition and fusion temperature. In the principal chains the oxidized CH₂-CH₂ bonds decomposed firstly. Since partly cross linking existed in the molecule chains, the indentation modulus and hardness first increased linearly and then decreased. And with the moisture ratio reducing firstly, the moisture-penetrability raised first and then fell.Besides, the theoretical calculation also approved that the CH₂-CH₂ bonds, especiallythe oxidized bonds, were the weakness of the system, while the oxidation product (?)and (?) were relatively steady. The photooxidation aging mechanisms ofParylene C films were studied by the analysis of experimental data and calculation results, which figured that it is a procedure of free radicals' action.Through the studies, an effective characterization method to represent variation information of structures and performances were founded, application for the nano-indentation tests in film materials are broadened, the photooxidation aging characteristics and environment adaptability are mastered, and the influence rules for photooxidation aging on Parylene C film are definited. The research results establish the basement for further broadening the protection and application of Parylene C film.