Vapor diffusion in porous/nonporous polymer coatings by dielectric sorption analysis

Abstract

The sorption of water vapor in various organic coatings (polyimide, polyamide 6.6 (PA6.6), epoxy, polymethyl methacrylate, low density polyethylene) and filters (polyvinylidene fluoride, polytetra-fluoro-ethylene, porous polyethylene, nitro cellulose, cotton linter) has been investigated by a technique called Dielectric Sorption Analysis (DSA). The technique is based on high-resolution time-resolved, capacitance measurements performed during exposure of an organic coating to humidified nitrogen. The DSA technique could distinguish between all samples, and the diffusion coefficient and maximum sorption is calculated for all samples. A frequency sweep with a dielectric analyzer showed that in all cases the water has no interaction with the polymer films, except PA6.6. For PA6.6 it is assumed that electrode polarization takes place. For filters a frequency sweep showed in two cases electrode polarization (porous polyethylene, cotton linter), two cases no interaction (polytetra-fluoro-ethylene, nitro cellulose) and two cases an intermediate effect (polyvinylidene fluoride 0.22 mm, polyvinylidene fluoride 0.45 mm). The filters described a desorption profile, likely due to swelling of the filters that caused the vapor to be pressed out of the pores of the filters. Mass transport properties derived from complementary weight measurements on epoxy films were in good agreement with the DSA results.

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