Solvent-Responsive\nGlass Transition Behavior of Polyelectrolyte\nComplexes

Polyelectrolyte complexes (PECs) have attracted considerable\nattention\nowing to their unique physicochemical properties and potential applications\nas smart materials. Herein, the glass transitions of PECs solvated\nwith varying alcohols are investigated in poly(diallyldimethylammonium)/poly(acrylic\nacid) (PDADMA/PAA) complexes by using modulated differential scanning\ncalorimetry (MDSC). Solvents with one or two hydroxyl groups are selected\nto examine the effect of PAA-solvent interactions on the glass transition\ntemperature (<i>T</i><sub>g</sub>). Except for glycerol,\nall alcohol solvents yield PECs with detectable <i>T</i><sub>g</sub>’s and plasticization behavior. Furthermore, a\nlinear relationship for 1/<i>T</i><sub>g</sub> and the natural\nlogarithm of the number of hydroxyl groups to intrinsic ion pair ratio\n[ln(<i>n</i><sub>hydroxyl</sub>/<i>n</i><sub>intrinsic‑ion‑pair</sub>)] is found. This result is significant because prior work demonstrated\nthe relationship only for water and no other solvents. All-atom molecular\ndynamics (MD) simulations analyze the ability of the solvent to form\nhydrogen bonds via the solvent’s OH groups to the PAA, revealing\nthat the solvent molecule size and available hydroxyl groups govern\nthe change in the glass transition. Overall, the clear dependence\nof a PEC’s glass transition on the solvent’s chemical\nstructure provides a simple guideline for predicting their relationship.