Effect of metal salts on high-voltage atmospheric cold plasma-induced polymerization of acrylamide

Abstract

Acrylamide polymerization in solution was successfully induced by high-voltage atmospheric cold plasma (HVACP) treatment, using nitrogen gas. Addition of metal sulfates greatly increased acrylamide polymerization, with ZnSO4 and MgSO4 yielding 89% and 62% polyacrylamide polymer, respectively. Presence of excited nitrogen species during HVACP treatment was demonstrated using optical emission spectroscopy. Proton NMR (H1NMR) and attenuated total reflectance-Fourier transform infrared spectroscopy were performed to verify the degree of polymerization. Rheology experiments and viscosity measurements showed that acrylamide samples treated with HVACP in the presence of ZnSO4, MgSO4 had higher viscoelastic moduli, and intrinsic viscosity (η) compared to those treated in deionized (DI) water, due to the higher degree of polymerization. Addition of ZnSO4 yielded the greatest viscoelastic moduli and intrinsic viscosity (the storage modulus was G' = 1.26·104 ± 1.8·103 Pa and the loss modulus was G" = 3.06·103 ± 1.10·103 Pa, and [η] ≈ 26 L/g). With MgSO4, the viscoelastic moduli were G' = 5.93·103 ± 1.40·103 Pa and G" = 1.60·103 ± 2.6·102 Pa, and (η) ≈ 4.7 L/g. In DI water G' = 1.55·103 ± 2.1·102 Pa and G" = 7.44·102 ± 1.37·102 Pa, and (η) ≈ 2. PAM prepared with ZnSO4 also had the highest molecular weight, as determined by mass spectroscopy. ZnCl2 and MgCl2 hindered acrylamide polymerization, highlighting the effect of the sulfate ions on acrylamide polymerization using HVACP treatment.