SURFACE PHOTODEGRADATION OF POLY(VINYLIDENE FLUORIDE) BY INNER-SHELL EXCITATION

Abstract

Poly(vinylidene fluoride) (PVDF, –( CH 2– CF 2)n–) shows the effective H + desorption induced by the irradiation of photon corresponding to the transition from carbon ( C ) 1s to σ( C – H )*. In order to clarify the effect of the C – H bond scission by the irradiation, near-edge X-ray absorption fine structure (NEXAFS) spectra and the kinetic energy (Ek) distribution of desorbed ion were observed. By the irradiation of photon near C 1s region, a new peak appears in the C 1s NEXAFS spectra at photon energy of 285 eV, which is about 3 eV lower than that of the lowest peak in the NEXAFS spectrum of the pristine PVDF film. The appearance of the lowest NEXAFS peak of irradiated PVDF film is assigned to the transition to π*. It indicates that the irradiation of photons near C 1s region introduces carbon–carbon double bonds into the backbone chain of PVDF. At early stage of X-ray exposure the yield of desorbed ion with low Ek (~ 2 eV) decreases rapidly. The ion with low Ek is assigned to H + desorbed from the sp3-hybrid state, which is characteristics of the pristine PVDF. It indicates that formation of double bonds in PVDF backbone chain makes the number of sp3-hybrid state decrease. This variation occurs by irradiation of photons corresponding to the transition from C 1s to σ( C – H )* more rapidly than that to the transition to σ( C – F )*.