The sorption of water vapor in Kapton® ͑polyimide͒ films has been investigated with a new method, dielectric sorption analysis ͑DSA͒. The technique is based on high-resolution time-resolved capacitance measurements performed during exposure of an organic coating to humidified nitrogen. The basis of the method is described together with experimental details related to the capacitance measurement, long-term stability, reproducibility, and other characteristics of the setup. The technique allows the determination of the sorption/desorption and diffusion characteristics of a coating on a time scale varying from seconds to days. Mass transport properties derived from complementary weight measurements are in good agreement with the DSA results. Real-time monitoring of the moisture sorption in organic coatings demonstrates the potential of the technique in the field of nondestructive coating inspection and testing.
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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