Polyelectrolyte complexes (PECs), formed by the association of oppositely charged polyelectrolytes in solution, undergo a glass transition-like event of an unclear nature. This transition event has been detected using calorimetry or mechanical techniques. Recent simulation work suggests that water with the polyelectrolyte undergoes a subtle dehydration process with increasing temperature. The observed thermal transition temperature (Ttr) is influenced by both the complexation condition and subsequent addition of water. Here, we present the influence of water on two pairs of PECs, poly(diallyldimethylammonium chloride) −poly(sodium 4-styrenesulfonate) (PDAC−PSS), and poly(allylamine hydrochloride)−poly(acrylic acid) (PAH−PAA), in which the PEC structure and composition are affected by preparation conditions, solution NaCl concentration or pH values. Modulated differential scanning calorimetry (MDSC) reveals a Ttr that decreases in value with increasing hydration and decreasing polyelectrolyte-polyelectrolyte ion pairing. We show the collapse of all Ttr values onto a single master curve when plotted against the ratio of water molecules per polyelectrolyte-polyelectrolyte ion pair. A hypothesis is proposed based on these results that hydrated PECs undergo a two-step thermal transition caused by an initial restructuring of the water-polyelectrolyte hydrogen-bonding network, followed by chain relaxation through the intrinsic compensation pairs.

Effect of water on the thermal transition observed in polyelectrolyte complexes

254th National Meeting (2017)

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