Solvent-Responsive Glass Transition Behavior of Polyelectrolyte Complexes

Abstract

Polyelectrolyte complexes (PECs) have attracted considerable attention owing to their unique physicochemical properties and potential applications as smart materials. Herein, the glass transitions of PECs solvated with varying alcohols are investigated in poly(diallyldimethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes by using modulated differential scanning calorimetry (MDSC). Solvents with one or two hydroxyl groups are selected to examine the effect of PAA-solvent interactions on the glass transition temperature (T_g). Except for glycerol, all alcohol solvents yield PECs with detectable T_g’s and plasticization behavior. Furthermore, a linear relationship for 1/T_g and the natural logarithm of the number of hydroxyl groups to intrinsic ion pair ratio [ln(n_hydroxyl/n_{intrinsic-ion-pair})] is found. This result is significant because prior work demonstrated the relationship only for water and no other solvents. All-atom molecular dynamics (MD) simulations analyze the ability of the solvent to form hydrogen bonds via the solvent’s OH groups to the PAA, revealing that the solvent molecule size and available hydroxyl groups govern the change in the glass transition. Overall, the clear dependence of a PEC’s glass transition on the solvent’s chemical structure provides a simple guideline for predicting their relationship.