title: The Role of Field Electron Emission in Polypropylene/Aluminum Nanodielectrics Under High Electric Fields.
abstract: Polymer/metallic particle nanocomposites or nanodielectrics can exhibit colossal dielectric constants with a relatively low dissipation factor under low electric fields and thus seem to be promising for high-energy density dielectric capacitors. To study this possibility, this work focused on the dielectric performance and loss mechanisms in polypropylene (PP)/aluminum nanoparticle (nAl NP) composites under high electric fields. Phosphonic acid-terminated poly(ethylene-co-1-butene) was grafted to the Al2O3surface layer on the nAl NPs in order to achieve reasonable dispersion in the PP matrix. The dielectric breakdown study showed that the breakdown strength decreased to nearly 1/20 that of the neat PP film as the nAl content increased to 25.0 vol %. The leakage current study revealed three electronic conduction mechanisms in the PP/100 nm nAl nanocomposites, namely, ohmic conduction at low fields, hopping conduction at intermediate fields, and Fowler-Nordheim (FN) field electron emission above a critical field, depending on the filler content. Compared to the 100 nm nAl NPs, smaller (e.g., 18 nm) nAl NPs needed a much higher electric field to exhibit FN field electron emission. It was the FN electron tunneling that induced a substantial reduction in breakdown strength for the PP/nAl nanocomposites. Meanwhile, electron-tunneling injected space charges (electrons) from nAl NPs into the PP matrix, and internal electronic conduction led to significant dielectric nonlinearity at high poling fields. Although polymer/metallic NP composites are not suitable for high-field electric applications, they can be good candidates for electrical switches and quantum tunneling composites operated at relatively low electric fields.
authors.affiliation: Center for Layered Polymeric Systems (CLiPS) and Department of Macromolecular Science and Engineering, Case Western Reserve University , Cleveland, Ohio 44106-7202, United States.
authors.forename: Guoqiang
authors.initials: G
authors.lastname: Zhang
authors.affiliation: College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University , Chengdu, Sichuan 610065, P. R. China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.affiliation: Center for Layered Polymeric Systems (CLiPS) and Department of Macromolecular Science and Engineering, Case Western Reserve University , Cleveland, Ohio 44106-7202, United States.
authors.forename: Saide
authors.initials: S
authors.lastname: Tang
authors.affiliation: Department of Chemistry and Biochemistry, Central Michigan University , Mount Pleasant, Michigan 48859, United States.
authors.forename: Rhett D
authors.initials: RD
authors.lastname: Thompson
authors.affiliation: Center for Layered Polymeric Systems (CLiPS) and Department of Macromolecular Science and Engineering, Case Western Reserve University , Cleveland, Ohio 44106-7202, United States.
authors.forename: Lei
authors.identifier: http://orcid.org/0000-0001-6570-9123
authors.initials: L
authors.lastname: Zhu
keywords: aluminum nanoparticles; electron tunneling; field electron emission; nanodielectrics; polypropylene