Sorption isotherms, sorption enthalpies, diffusion coefficients and permeabilities of water in a multilayer PEO/PAA polymer film using the quartz crystal microbalance/heat conduction calorimeter

Sorption isotherms, sorption enthalpies, and diffusion coefficients for water in an 11 μm thick PEO/PAA multi-layer film have been measured at 30, 40, and 60 °C for relative humidities between 0 and 70%. All quantities were measured on the same film using the quartz crystal microbalance/heat conduction calorimeter. Water diffusion coefficients in the film are several orders of magnitude lower than in the separate components. Sorption isotherms are of type III at 30 and 40 °C and linear at 60 °C. Water vapor permeabilities are calculated as the product of Henry's law solubility and diffusion coefficient. The permeability of the PEO/PAA multilayer film is exceedingly low compared to other polymer films used as membranes. The enthalpy of water sorption determined from the sorption isotherms using the van’t Hoff relation is 32.9 ± 0.3 kJ/mol. Calorimetric enthalpies of water sorption range from 42 to 34 kJ/mol at 30 and 40 °C over the humidity range studied. The change in motional resistance, a quantity proportion to the loss compliance of the film, has also been recorded at all three temperatures, and a common trend is an increase in loss compliance with increasing relative humidity, indicating plasticization of the film by water.