Fabrication of ion track membrane of fluoropolymer by irradiation of a uniform beam in oxygen

Kitamura, Akane; Yamaki, Tetsuya*; Yuri, Yosuke*; Koshikawa, Hiroshi*; Sawada, Shinichi*; Yuyama, Takahiro*

Ion track membranes of polyvinylidene fluoride (PVDF) are produced by chemical etching using a strong oxidant in an alkali solution after irradiation with an ion beam in vacuum. The oxidant erodes not only ion tracks but also a pristine surface of PVDF. Therefore, it causes serious deterioration in the quality of PVDF membranes. We have developed a track etching technique without any oxidant by irradiation with an ion beam in an oxygen atmosphere. PVDF films were irradiated with 330-MeV Ar ions in an oxygen atmosphere using a uniform-beam formation/irradiation system developed at the AVF-cyclotron of the TIARA facility. The maximum etching rate was six times faster than that from the conventional method; furthermore, the maximum diameter of track-etched pores was more than twice as large as that in the conventional method. FT-IR results showed that more oxygen-containing functional groups were formed on the surface irradiated in an oxygen atmosphere. Those were both caused by oxidation of ion tracks and the oxidation of ion tracks widened the size of etchable ion tracks. This suggests that the irradiation in oxygen can provide a useful technique of an oxidant-free track-etching process.