Water uptake of water-borne paint resin films as studied by impedance spectroscopy and gravimetry

Impedance spectroscopy and gravimetry were employed to characterize alkyd-acrylate and styrene-acrylate water-borne resin film properties during wetting-through (i.e. during water uptake).The results were obtained by (i) measuring the weight of the resin films during soaking in solution and by (ii) measuring impedance of the film between two electrolyte contacts in a two-compartment electrochemical cell. Both methods characterize the effect of dilute solution upon film properties: gravimetry yields a direct measure of water content; impedance spectroscopy enables us to characterize dielectric and ion transport properties of the film.By evaluating the measured data, we were able to distinguish the following processes taking place when a dry resin film got in contact with a solution: (i) penetration of the solution into macro-pores that form transfer paths of the dry resin; (ii) structural changes of the polymer molecules due to swelling; (iii) transport of charge holding species within the polymer.The polymer properties, namely, swelling ability and conductivity were studied and were found to be different for two types of water-borne resins. The physically drying styrene-acrylate resin is more porous and is more apt to swell than the oxidatively drying alkyd-acrylate resin.