Random copolymer gels of N-isopropylacrylamide and N-ethylacrylamide: effect of synthesis solvent compositions on their properties

Random copolymer gels of N-isopropylacrylamide (NIPAM) and N-ethylacrylamide (NEAM) were synthesized using a 1 : 1 monomer molar ratio in different methanol-water (x_m = 0, 0.06, 0.13, 0.21, 0.31 0.43, 0.57, 0.76, where x_m = mole fraction of methanol) mixtures. The samples were characterized using different techniques like Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), swelling ratio measurements, deswelling kinetics study, atomic force microscopy (AFM), and rheology. We found that, with the variation of the solvent composition (methanol-water mixtures) the properties of the gels varied significantly. These results can be explained on the basis of the interactions of the two different kinds of monomers with different methanol-water mixtures, their different kinds of thermoresponsiveness and hydrophilicity, and their different cononsolvent properties toward methanol-water mixtures.