Perfluorosulfonate ionomers (PFSI's), the most common being Nafion from DuPont, are copolymers of tetrafluoroethylene and a perfluorovinyl ether comonomer with a terminal sulfonic acid functionality, typically composing less than 15 mole percent of the copolymer. Phase separation between the hydrophobic chain matrix and the polar sulfonate groups create a microphase separated morphology with ionic functionalities aggregating into "clusters" held together by strong, Coulombic attractive forces. PFSI morphology is further complicated by the organization of backbone segment into "PTFE-like" crystalline regions in the matrix. Ionic aggregation results in unique transport properties making PFSI's applicable in multiple electrochemical devices, particularly Proton Exchange Membrane fuel cells.
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