Solution properties of nafion in methanol/water mixture solvent

• Published in: Polymer (Guilford) Vol. 45; no. 8; pp. 2853 - 2862
• Main Authors: Lee, Su-Jen, Yu, T.Leon, Lin, Hsiu-Li, Liu, Wen-Horng, Lai, Chen-Lan
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2004; Elsevier
• Subjects: Applied sciences; Dynamic light scattering; Exact sciences and technology; Nafion solutions; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Viscoelasticity; Viscoelasticity; Dynamic light scattering; Nafion solutions; Ionomer; Experimental study; Mechanism; Sulfonate copolymer; Tetrafluoroethylene copolymer; Mixed solvent; Solution structure; Concentration effect; Dilute solution; Molecular aggregation; Alcoholic solution; Aqueous solution
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2004.01.076

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 (∼10 3 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 (∼10 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 –SO 3 − 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.