Water and Ion Pairing Universally Influence the Glass Transition of Polyelectrolyte Complexes
Yanpu Zhang (1), Piotr Batys (3,4), Joshua T O’Neal (2), Fei Li (1), Maria Sammalkorpi (3), and Jodie L. Lutkenhaus (1,2)
1. Artie McFerrin Department of Chemical Engineering
2. Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843, United States
3. Department of Chemistry and Materials Science, Aalto University, P.O. Box 16100, 00076 Aalto, Finland
4. Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, PL-30239 Krakow, Poland
The glass transition of a polyelectrolyte complex is long known to be influenced by hydration and salt doping. For example, it is generally accepted that increasing water content or salt doping depresses the glass transition temperature (Tg). However, there lacks a quantitative and physically meaningful relationship among these parameters that captures the behavior across more than one polyelectrolyte complex system. Here, modulated differential scanning calorimetry and all-atom molecular dynamic simulations are cooperatively exploited to investigate complexes paired from poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). This relationship reveals that the glass transition is quantitatively controlled by the number of water molecules surrounding polyelectrolyte-polyelectrolyte ion pairs. Specifically, ln(nH2Onintrinsic ion pair) ~ 1/Tg. Because this relationship also holds for another different polyelectrolyte complex system, it suggests that it might be considered “universal”. Simulations reveal the extent of water clustering around different types of ion pairs during the glass transition process. These results explain broadly the fundamental - but nontraditional - plasticization influence of water, which impacts current interpretations of PECs for humidity annealing, temperature-responsive platforms, swelling, and sensing for a wide range of applications.
Keywords: Polyelectrolyte, glass transition, water, salt doping