The dynamic mechanical and rheological behavior of polyelectrolyte coacervates and complex precipitates is of interest for many applications ranging from health to personal care. Hydration is an important factor, but its effect on the dynamic properties of polyelectrolyte complexes (PECs) is poorly understood. Previously in our group, time-temperature and time-water superposition principles were applied to the dynamic mechanical properties of PECs prepared from poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), showing equivalency between temperature and water. However, information is lacking regarding the relaxation time of the intrinsic ion pair in these PECs at different pH values and the role played by water. Here, we describe the dynamic mechanical behavior of PAH-PAA solid precipitates at different pH values (4.5, 5.5 and 7), hydration and temperature. The temperature shift factor obtained after performing time-temperature superposition principle at a fixed pH value and humidity followed an Arrhenius relation. The water shift factor obtained after time-water superposition enabled the study of the relaxation time of intrinsic ion pairs at different water content. The relaxation time of the intrinsic ion pair at different water contents for all of the studied pH values followed the resulting relationship: . Differential scanning calorimetry experiments were performed to quantify the amount of “bound water” in PAH-PAA complexes at different pH values and hydrations. It was shown that bound water provides a major contribution to plasticization and relaxation of these PECs.

Dynamic mechanical response of solid polyelectrolyte complexes at varying temperature, humidity and pH

ACS Spring Meeting 2021

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