The Effect of Hydrophobic Interactions on the Relaxation Dynamics of Polyelectrolyte Complex Coacervates

We investigate the effect of hydrophobic interactions on the relaxation dynamics of polyelectrolyte complex (PEC) coacervates. We prepare bulk, salt-free PECs composed of poly([2-(methacryloyloxy)ethyl]trimethylammonium)) (PMETA) and poly(3-(methacryloyloxy)propane-1-sulfonate (PMAPS) copolymerized with either poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA), which is hydrophilic, or poly(lauryl methacrylate) (PLMA), which is hydrophobic. Coacervate samples with identical polymer concentrations and varying salt concentrations were prepared by direct mixing of PEC, water, and salt. We find that the salt resistance of the hydrophobic samples is higher than that of the hydrophilic samples, and hydrophobicity increased the viscosities and relaxation times of the materials. These trends are consistent with hydrophobic interactions providing “sticky” interactions that slow the relaxation dynamics of the coacervates, and suggest that hydrophobic interactions should be accounted for when interpreting rheological data on these materials.