title: Simulation study of sulfonate cluster swelling in ionomers.
abstract: We have performed simulations to study how increasing humidity affects the structure of Nafion-like ionomers under conditions of low sulfonate concentration and low humidity. At the onset of membrane hydration, the clusters split into smaller parts. These subsequently swell, but then maintain constant the number of sulfonates per cluster. We find that the distribution of water in low-sulfonate membranes depends strongly on the sulfonate concentration. For a relatively low sulfonate concentration, nearly all the side-chain terminal groups are within cluster formations, and the average water loading per cluster matches the water content of membrane. However, for a relatively higher sulfonate concentration the water-to-sulfonate ratio becomes nonuniform. The clusters become wetter, while the intercluster bridges become drier. We note the formation of unusual shells of water-rich material that surround the sulfonate clusters.
authors.affiliation: Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Elshad
authors.initials: E
authors.lastname: Allahyarov
authors.forename: Philip L
authors.initials: PL
authors.lastname: Taylor
authors.forename: Hartmut
authors.initials: H
authors.lastname: Löwen
mesh_terms: D003198:Computer Simulation; D007477:Ions; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry*; D013451:Sulfonic Acids / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D007477:Ions; D011108:Polymers; D013451:Sulfonic Acids; D014867:Water