Dilute solution properties of Nation 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 (similar to10(3) nm) rod-like aggregation particles, which can be dissociated into single molecular chains by dissolving Nation in propanol/water mixture solvents, is attributed to the hydrophobic interaction of fluorocarbon backbone. The secondary aggregation process causes formation of larger aggregation particles (similar to10(4) 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* similar toaround 1.0 mg/ml and C** similar toaround 5.0 mg/ml in the present study, where transitions of Nafion aggregation conformations occur. C* is the concentration at which most of the Nation 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. (C) 2004 Elsevier Ltd. All rights reserved.