期刊
ELECTROCHIMICA ACTA
卷 133, 期 -, 页码 283-293出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2014.04.002
关键词
Epoxy; Photo-oxidative; Microstructures; Water barrier properties
资金
- National Natural Science Foundation of China [21174108, 11205118, J1210061]
- Fundamental Research Funds for the Central Universities [20102020201000017]
- Large-scale Instrument And Equipment Sharing Foundation of Wuhan University [LF20120183]
Evolution of chemical functional groups, microstructure and water barrier properties of a polyamidecured epoxy (diglycidyl ether of bisphenol-A epoxy resin, DGEBA) coating during ultraviolet A (UV-A) photo-oxidative aging is systematically investigated. At the early stage of aging, decrements of S parameter and water uptake coefficient indicate the formation of a more compact structure induced by the post-curing process. After 208 hours (h) of UV irradiation, a novel time constant at relatively high frequency (3.5 x 10(2) Hz) appears in the electrochemical impedance spectroscopy (EIS) spectra suggesting that a microporous layer generates near the surface of DGEBA film. With the increase in irradiation time, overlap of two time constants at frequencies around 18 Hz and 3.7 x 10(3) Hz is observed after 1.33 h of immersion, indicating that the micropores grow towards the bulk and form more characteristic layers with microporous structures. After irradiation for 399 h, a low S parameter region near the sample surface is observed, which implies that a surface layer with low free volume may have formed. With longer exposure, EIS results also reveal that the water barrier property of the coating can be improved, which confirms the formation of the denser surface layer near the surface as a result of radical recombination during UV-A treatment. (C) 2014 Elsevier Ltd. All rights reserved.
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