title: Structure-Property Relationships in Hydroxide-Exchange Membranes with Cation Strings and High Ion-Exchange Capacity.
abstract: A series of poly(2,4-dimethyl-1,4-phenylene oxide) hydroxide-exchange membranes (HEMs) with cation strings containing a well-defined number of cations (CS-n) and similar, high ion-exchange capacities are synthesized to investigate the effect of cation distribution on key HEM properties. As the number of cations on each string grows, the size of the ionic clusters increases from 10 to 55 nm. Well-connected ion pathways and a hydrophobic framework are observed for n≥4. The enhanced phase segregation increases the hydroxide conductivity from CS-1 to CS-6 (30 to 65 mS cm(-1) ) and suppresses the water uptake (from 143 % to 62 %). Moreover, molar hydroxide conductivities for CS-n membranes show two distinctive stages as n increases: ∼23 S cm(2)  mol(-1) for n≤3; and ∼34 cm(2)  mol(-1) for n≥4.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA.
authors.forename: Junhua
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Gu
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA.
authors.forename: Ruichang
authors.initials: R
authors.lastname: Xiong
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA.
authors.forename: Bingzi
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA. bxu@udel.edu.
authors.forename: Bingjun
authors.initials: B
authors.lastname: Xu
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA. yanys@udel.edu.
authors.forename: Yushan
authors.initials: Y
authors.lastname: Yan
mesh_terms: D015195:Drug Design; D006878:Hydroxides / Q000737:chemistry*; D007474:Ion Exchange; D008567:Membranes, Artificial; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry; D013329:Structure-Activity Relationship
chemical_list: D006878:Hydroxides; D008567:Membranes, Artificial; D011108:Polymers
keywords: cation; fuel cell; hydroxide-exchange membrane; morphology; phase separation