title: Role of Amphiphilic Block Copolymer Composition on Pore Characteristics of Micelle-Templated Mesoporous Cobalt Oxide Films.
abstract: Block copolymer templating is a versatile approach for the generation of well-defined porosity in a wide variety of framework chemistries. Here, we systematically investigate how the composition of a poly(methoxy poly[ethylene glycol] methacrylate)-block-poly(butyl acrylate) (PMPEG-PBA) template impacts the pore characteristics of mesoporous cobalt oxide films. Three templates with a constant PMPEG segment length and different hydrophilic block volume fractions of 17%, 51%, and 68% for the PMPEG-PBA are cooperatively assembled with cobalt nitrate hexahydrate and citric acid. Irrespective of template composition, a spherical nanostructure is templated and elliptical mesostructures are obtained on calcination due to uniaxial contraction of the film. The average pore size increases from 11.4 ± 2.8 to 48.5 ± 4.3 nm as the length of the PBA segment increases as determined from AFM. For all three templates examined, a maximum in porosity (∼35% in all cases) and surface area is obtained when the precursor solids contain 35-45 wt % PMPEG-PBA. This invariance suggests that the total polymer content drives the structure through interfacial assembly. The composition for maximizing porosity and surface area with the micelle-templating approach results from a general decrease in porosity with increasing cobalt nitrate hexahydrate content and the increasing mechanical integrity of the framework to resist collapse during template removal/crystallization as the cobalt nitrate hexahydrate content increases. Unlike typical evaporation induced self-assembly with sol-gel chemistry, the hydrophilic/hydrophobic composition of the block copolymer template is not a critical component to the mesostructure developed with micelle-templating using metal nitrate-citric acid as the precursor.
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Siyang
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Pattarasai
authors.initials: P
authors.lastname: Tangvijitsakul
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Qiang
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Sarang M
authors.initials: SM
authors.lastname: Bhaway
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Kehua
authors.initials: K
authors.lastname: Lin
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Cavicchi
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Soucek
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325-0301, United States.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Vogt