Solution properties of nafion in methanol/water mixture solvent

Dilute solution properties of Nafion in methanol/water (4/1 wt ratio) mixture solvent with Nafion concentrations ranging from 0.2 to 9.0 mg/ml was studied using membrane osmometer, viscoelasticity analyzer, and dynamic light scattering. Two aggregation processes were observed. The primary aggregation process causes formation of smaller sizes (∼10³ nm) rod-like aggregation particles, which can be dissociated into single molecular chains by dissolving Nafion in propanol/water mixture solvents, is attributed to the hydrophobic interaction of fluorocarbon backbone. The secondary aggregation process causes formation of larger aggregation particles (∼10⁴ nm), which can be dissociated into primary aggregation particles by mixing NaCl salt into Nafion/methanol/water solutions, is attributed to the ionic aggregation of primary aggregation particles which arise from the electrostatic attraction of Nafion side chain -SO₃⁻ ion pairs. Two critical concentrations were observed in this concentration regime, i.e. C∗∼around 1.0 mg/ml and C∗∗∼around 5.0 mg/ml in the present study, where transitions of Nafion aggregation conformations occur. C∗ is the concentration at which most of the Nafion primary rod-like perfluoro backbone aggregation particles aggregate to form secondary ionic aggregations. C∗∗ is the concentration at which the disordered segments of primary aggregation particles start to overlap and self-assemble.