title: Nanophase segregation and water dynamics in the dendrion diblock copolymer formed from the Fréchet polyaryl ethereal dendrimer and linear PTFE.
abstract: We propose a new material consisting of a dendrion copolymer formed from (a) a water-soluble dendritic polymer and (b) a hydrophobic backbone. Using molecular dynamics simulations techniques, we determine the structure and dynamics of the dendrion formed by second-generation Fréchet polyaryl ethereal dendrimer as the hydrophilic component and linear polytetrafluoroethylene (PTFE) as the hydrophobic polymer, with 5 and 10 wt % of water. We find that this material produces a well-developed nanoscale structure in which water forms a continuous nanophase, making this new family of compounds promising candidates for applications in fuel cell membranes. We find that the water molecules are incorporated into the dendrimer block of the copolymer to form a nanophase-segregated structure. The well-developed nanophase-segregated structures rendered by this material have characteristic dimensions of segregation ( approximately 30 Angstrom) and dendrimer conformational properties that are independent of water content. Calculations of water dynamics and proton transport in these nanophase-segregated structures indicate that the dendrion copolymer membrane with 10 wt % of water content has a water structure and transport properties equivalent to that of the hydrated Nafion membrane with 20 wt % of water content.
authors.affiliation: Materials and Process Simulation Center (MC 139-74), California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Seung Soon
authors.initials: SS
authors.lastname: Jang
authors.forename: Shiang-Tai
authors.initials: ST
authors.lastname: Lin
authors.forename: Tahir
authors.initials: T
authors.lastname: Cagin
authors.forename: Valeria
authors.initials: V
authors.lastname: Molinero
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
mesh_terms: D050091:Dendrimers / Q000737:chemistry*; D036103:Nanotechnology; D011138:Polytetrafluoroethylene / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D050091:Dendrimers; D014867:Water; D011138:Polytetrafluoroethylene