Gas-Permeation Control by PET Membranes with Nanosized Pores

Abstract

KEY WORDSGas-Permeation / PET / Heavy-ion Irradiation / Etching / Nanosized Pore / Knudsen Flow / PET is a polymer widely used for fibers, films, and bottles. The gas permeability properties of PET, which is often used as a gas-barrier film, can easily be modified using techniques such as ion irradiation. PET membranes have higher mechanical strength and undergo various chemical changes in response to ion irradiation easily and thus are optimum material for gas-permeation membrane. [1][2][3][4][5][6] We previously reported the effects of heavy-ion irradiation on the gas permeation of a PET membrane.7 A portion of the heavy-ion irradiated PET membranes exhibits Knudsen flow during gas-permeation measurement. Energetic heavy ions are ionizing particles that create zones of high-density excitations and ionizations as they pass through membrane materials and cause many effects due to a high local dose within ion tracks. We thus applied etching utilizing NaOH solution as an etchant control nanosized pores of the heavy ion-irradiated PET membranes. In the past, much attention was paid to track etching in various polymer membranes with respect to applications in nuclear fusion, medical, material technology and other fields. [8][9][10][11][12][13][14][15][16] In the present study, PET membranes were irradiated at a fluence of 3 Â 10 9 ions/cm 2 and etched in 6N or 1N NaOH solution at 60 C. Etching time was controlled to observe changes in the gas-permeation behavior depending on the etching. Pore-size distribution in the membranes exhibiting Knudsen flow during gas-permeation measurement was observed using the nano-permporometer and permporometer. EXPERIMENTALThe poly(ethylene terephthalate) (PET) membrane used in this study was obtained from Hoechst Japan Co., Ltd. Thickness of the PET membrane was 12 mm, and each had a semicrystalline structure of approximately 40 % crystallinity and density of 1.4 g/cm 3 . Xe ions were used at a fluence of 3 Â 10 9 ions/cm 2 for heavy-ion irradiation. A PET membrane of 12 mm thickness was cut into a 50 Â 50 mm squares and then attached to a glass 50 Â 50 Â 1 mm plate. The chamber for formation of the ion-track pores in the membrane, connected to the Azimuthally Varying Field (AVF) cyclotron in the Takasaki Ion Accelerators for Advanced Radiation Applications (TIARA), Japan Atomic Energy Research Institute (JAERI), was designed for alternate use of turntable-type and roll-type film-carrying systems. Irradiation was performed under vacuum. The apparatus for Xe ion irradiation has been described previously. 7We applied etching using NaOH solution to control nanosized pores. PET membranes irradiated at a fluence of 3 Â 10 9 ions/cm 2 were etched in 6N or 1N NaOH solution at 60 C as shown in Figure 1. Etching time was controlled to observe changes in the gas-perEtching 1N or 6N -NaOH Temperature: 60°C Figure 1. Illustration of the nuclear track membrane-production method.

Hexagonal Boron Nitride-Coated Polyimide Ion Track Etched Separator with Enhanced Thermal Conductivity and High-Temperature Stability for Lithium-Ion Batteries

“…37 Latent tracks in polymer films are subsequently etched with specific chemical reagents depending on the chemical properties of the trunk polymer to form TEMs with pores or channels. 38 Currently, TEMs are used for sizeselective filtration and separation in medical and biochemical applications, 10 gas permeation, 39 electrophoresis, 40 biological and chemical sensors, 41 optical sensors, 42 Li−S battery separators, 43 ion-selective devices, 44 and templates for the growth of hydrogels and nanowires of metals, semiconductors, and insulators. 45,46 In this study, a PI/hBN separator was successfully fabricated by combining a heavy ion track etching technique and a doctor blade coating method to achieve highly safe LIBs.…”