Viscosity Scaling of Diallyl-Dimethyl-Ammonium Chloride Polyelectrolytes in Aqueous and Salt Solutions

A better understanding of the different concentration regimes that exist for polyelectrolytes can be helpful to create membranes for anion exchange with applications including electrolysis and fuel cells. Viscosity scaling is a method used to study various concentration regimes in polymer and polyelectrolyte solutions. The objective of this study was to perform the viscosity scaling for two cationic polyelectrolytes in water and 0.1 M NaCl: a co-polymer Poly(acrylamide-co-diallyl-dimethyl-ammonium chloride)(PAAcDMAC) and a homopolymer Poly(diallyl-dimethyl-ammonium chloride) (PDADMAC). Concentrations from 0.25 to 18 wt% polymer spanned from dilute to entangled concentration regimes. Higher concentrations provided insight on the semi-dilute and entangled regimes, which have not been extensively studied. Comparing the PAAcDMAC in 0.1 M NaCl in the dilute region, 0.25 to 1.0 wt%, the ions from the salt interact and screen some of the electrostatic interactions. As a result, the polymer assumed a more compact conformation and viscosity decreased. Thus, in DI water, the electrostatic interactions of PAAcDMAC repel each other and cause the chain to elongate. This finding confirms previous studies on polyelectrolyte rheology. At concentrations above the dilute regime, the effects of salt solution versus water decreased until little difference in viscosity existed for PAAcDMAC. PAAcDMAC in DI water encompassed all four concentration regimes, and PAAcDMAC in NaCl exhibited three concentration regimes. Similar concentration regimes were measured for PDADMAC solutions. Beyond flow viscosity measurements, the viscoelasticity was measured using small amplitude oscillatory shear and large amplitude oscillatory shear.