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

Abstract

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 hydrogen-bonded 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 (T_g) 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 (a_T) is fitted to Arrhenius and Williams-Landel-Ferry (WLF) equations before and after T_g, respectively. Instead of the value of RH, the equilibrium water ratio in the polymer complex is used to describe humidity-dependent shift factor (a_W), which fits two log-linear 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 (f_c) to describe how the temperature and humidity working together and coupling effect.