In situ water permeation measurement using an external 3He 2+ ion beam

Abstract

A new approach for water vapour transmission rate (WVTR) measurement is demonstrated that uses an external ion beam. ‘Sandwich’ specimens were prepared comprising two films of the barrier material (PET) surrounding a thin film of hydrophilic poly(ethylene-oxide), “PEO”. Deuterated water (D 2O) permeating PET barrier films was trapped by the PEO, and quantified using 3He 2+ nuclear reaction analysis and proton detection. WVTR was determined from the rate of D 2O accumulation in the PEO layer. This approach may be applied both to poor barrier films with WVTRs of >200 g m −2 day −1, and may extend to films whose barrier properties exceed levels that can be characterised with conventional techniques. Variation in the proton energy distribution provides a means of measuring D 2O migration within test samples, and could be used to detect the approach to failure in complex barrier films. In these experiments, D 2O migration toward the irradiated face of the sample was attributed to ion beam-induced reactive sites or increased hydrophilicity of the barrier film, and was verified by separate measurements of the D 2O content of PET films. Strategies for improving the sensitivity and accuracy of this method for WVTR characterisation towards a lower detection limit 1 μg m −2 day −1 are discussed.