Tritiated water permeation and sorption in polyimide film

The transport of tritiated water through polyimide film in the temperature range 278-313 K was measured utilizing a permeation measurement system designed by the authors. Basically, it consists of a flow system equipped with water bubblers. The amount of tritiated water permeated through a polymer is evaluated from the concentration rise of tritium in the bubblers. The permeability coefficient of tritiated water through polyimide decreased with increasing temperature. Pre-exponential factor and activation energy of the permeability coefficient were found to be (2 ± 1) × 10 ^-14 kmol m m ^-2 s ^-1 kPa ^-1 and -5 ± 2 kJ mol ^-1, respectively. This negative activation energy agrees with results published by Okamoto et al. The enthalpy of the tritiated water solubility was determined to be -34 ± 13 kJ mol ^-1. Since permeation can be described by a one-dimensional diffusion model, the diffusion coefficient can be obtained from the quotient of permeability coefficient and solubility. The activation energy for the diffusion of water through polyimide was calculated to be 29 ± 13 kJ mol ^-1.