title: Gradient Films of Pristine Graphene/Pyrene-Functional Copolymers with Janus Electrical Properties.
abstract: We describe the first preparation of polymer-supported pristine graphene thin films with dramatically different electrical conductivities on the top and bottom surfaces. Pyrene-functional stabilizers based on polystyrene or poly(methyl methacrylate) were first synthesized by copolymerization of their monomers with 1-pyrenemethyl methacrylate. Stable dispersions of pristine graphene nanosheets were prepared by sonication of graphite in chloroform solutions of the pyrene-functional copolymers. Vacuum filtration of the polymer-stabilized graphene dispersions through a porous PTFE filter produces films with an internal gradient in nanosheet concentration. This gradient graphene concentration results in an electrically conductive, graphene-rich surface on one side of the composite film and a nonconductive, polymer-rich surface on its other side. Electrical conductivities ranging from 60 to 194 S/m are measured on the graphene-rich surface, which are among the highest conductivities reported for pristine graphene/polymer composites. Through scanning electron microscopy and secondary ion mass spectrometry characterization, these films were found to contain three distinct layers: a polymer-rich top surface, a transition layer with a gradient in nanosheet concentration, and a buckypaper-like bottom layer consisting of densely packed, highly oriented graphene nanosheets. The gradient structure of these films and their Janus-like electrical conductivity has potential applications in graded coatings for radiofrequency and optical devices.
authors: Artie McFerrin Department of Chemical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors: Dorsa
authors: D
authors: Parviz
authors: Department of Chemical Engineering, Texas Tech University , Lubbock, Texas 79409, United States.
authors: Ziniu
authors: Z
authors: Yu
authors: Materials Characterization Facility, Texas A&M University , College Station, Texas 77843, United States.|Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors: Stanislav
authors: S
authors: Verkhoturov
authors: Artie McFerrin Department of Chemical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors: Micah J
authors: MJ
authors: Green
authors: Department of Chemical Engineering, Texas Tech University , Lubbock, Texas 79409, United States.
authors: Ronald C
authors: RC
authors: Hedden
keywords: gradient composite film; poly(methyl methacrylate); polystyrene; pristine graphene; pyrene