Thermal and Electrical Transport Properties of Sheared and Un-Sheared Thin-Film Polymer/CNTs Nanocomposites
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Thermal and Electrical Transport Properties of Sheared and Un-Sheared Thin-Film Polymer/CNTs Nanocomposites Parvathalu Kalakonda1,4, Georgi Y. Georgiev2,3, Yaniel Cabrera3, Robert Judith3, Germano S. Iannacchione1, and Peggy Cebe3 1
Department of Physics, Worcester Polytechnic Institute, Worcester, MA, 01609, USA Department of Natural Sciences - Physics, Assumption College, Worcester, MA, 01609, USA 3 Department of Physics, Tufts University, Medford, MA, USA 4 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA 2
ABSTRACT Transport properties have been measured transverse to the plane of sheared and un-sheared thin-film nanocomposites of isotactic Polypropylene (iPP) and multiwall carbon nanotubes (MWCNTs) at various MWCNT concentrations. The sheared samples were processed in the melt at 200 0C at 1 Hz in a Linkan microscope shearing hot stage. The thermal and electrical conductivity measurements were performed on the same cell arrangement with the transport perpendicular to the thin-film plane using a DC method. The thermal and electrical conductivity perpendicular to the surface of the films are higher for the un-sheared as compared to the sheared samples. Interestingly, the percolation threshold appears smeared in both conductivity measurements likely due to pressing and shear treatment of the films, or the spacing between the data points. Important for electronics packaging and materials for which those anisotropic properties are highly desired this work presents important advances in understanding the structure-transport property relations. INTRODUCTION Polymers are typically very good thermal and electrical insulators while carbon nanotubes (CNTs) have very high thermal and electrical conductivity as well as large anisotropy between properties measured parallel or perpendicular to the CNT long axis. The questions explored in this study are aimed at the interplay between nanoscale and macro-scale phenomena in thin polymer/MWCNTs nano-composite (PNC) films. Macro-scale manipulation, like melt-shearing, structural alignment of polymer nano-composites, can induce nanoscopic order of the MWCNTs and polymer chains [1-3]. Here, it is investigated how the induced nanoscopic orientational order of MWCNTs and polymer chains affects macroscopic properties, namely the electrical and thermal conductivities of the films and their anisotropies [4-6]. There are many factors that can affect the percolation threshold of MWCNTs, like concentration, dispersion and size. The orientational order of MWCNTs is another factor which can influence the critical concentration when MWCNTs start forming networks. Combining polymer and carbon nanotubes nano-composites should allow for tunable composite material characteristics [7]. The conventional method to enhance electrical and thermal conductivity of polymers is to compound the polymer with conductive carbon nanotubes. In this case with increasing CNT content the electrical and thermal conductivities increase by order of magnitude at t
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