Dynamics of hydrogen-bonded polymer complexes of poly(ether oxide) and poly(acrylic acid): time-humidity-temperature equivalence

The dynamics of polymer complexes over long-time scales are critical for their applications across various fields. Humidity is a very important environmental parameter and its coupling with temperature significantly affects the performance of polymer complex materials. However, the understanding of humidity effect on hydrogenbonded polymer complex is poor and the quantitative studies are lacking. Here, we investigate the static and dynamic mechanical properties of hydrogen-bonded polymer complexes of poly(ethylene oxide) (PEO) and poly (acrylic acid) (PAA) and its reinforced derivatives under different humidity and temperature. When PEO/PAA complexes are reinforced through covalent cross-linking and coordination, both the humidity-induced glass transition and the glass transition temperature (Tg) increase. The equilibrium water uptake as a function of relative humidity (RH) shows two distinct trends, and the trend transition corresponds to the humidity-induced glass transition. Time-humidity equivalence and time-temperature equivalence are applied separately to construct the master curves. The temperature-dependent shift factor (aT) is fitted to Arrhenius and WilliamsLandel-Ferry (WLF) equations before and after Tg, respectively. Instead of the value of RH, the equilibrium water ratio in the polymer complex is used to describe humidity-dependent shift factor (aW), which fits two loglinear equations before and after humidity-induced glass transition. Furthermore, we combine humidity and temperature to do superposition to build the master curve of much longer timescale, and propose a coefficient (fc) to describe how the temperature and humidity working together and coupling effect.