Sorption and transport of water vapor in amphiphilic block copolymer films

Water vapor sorption in films consisting of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic block copolymers has been measured gravimetrically at air relative humidity in the range 38-94% at 24°C. The water sorption isotherm was obtained and compared to data for water vapor desorption (drying) for the same system. The kinetics of water vapor sorption were determined. The percentage of water gain is initially a linear function of square root of time, indicating Fickian diffusion in the block copolymer films. Diffusion models were used to fit the experimental results and to extract water diffusion coefficient values in the block copolymer film, the internal structure of which was initially semicrystalline (due to PEO) and, above ∼12% water, lamellar lyotropic liquid crystalline.