Four-electrode EIS as a dielectric tool to probe relaxational dynamics of free-standing PA6 films

This study focused on the relaxational dynamics of free-standing polyamide 6 (PA6) films immersed in NaCl solutions of varying concentrations (0.5 M, 2 M, and 4 M), using electrochemical impedance spectroscopy (EIS) in a four-electrode configuration. The impedance spectra domains used to identify dielectric markers were compared with broadband dielectric spectroscopy (BDS). The methodology allowed the simultaneous analysis of water absorption kinetics, molecular mobility, and charge transport. It was shown that for the PA6, water uptake cannot be accurately quantified from EIS data using traditional rule of mixture due to overlapping contributions from dipolar relaxations. The time constant observed in the EIS spectra was attributed to the dielectric manifestation of the glass transition ( α -mode) which became clearly distinguishable once water saturation was reached. The dielectric response of the PA6 followed Jonscher’s “universal” law, with high-frequency behavior dominated by capacitive properties and low-frequency by charge transport. Increasing the NaCl concentration resulted in decreased water uptake (from 7.0 vol.% to 4.1 vol.%), slower plasticization kinetics, and reduced charge transport, as shown by EIS, gravimetry, near-infrared spectroscopy (NIR) analysis, and differential scanning calorimetry (DSC) measurements. Overall, this study demonstrated the effectiveness of four-electrode EIS for probing polymer dynamics in immersion and highlighted the value of combining complementary techniques for a comprehensive understanding.