iPP/CNTs Multifunctional Polymer Nanocomposite

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iPP/CNTs Multifunctional Polymer Nanocomposite Parvathalu Kalakonda1, Sabyasachi Sarkar1, Erin A. Gombos2, Georgi Yordanov Georgiev2,3*, Germano Iannacchione1 and Peggy Cebe3 1

Department of Physics, WPI, Worcester, MA 01609, U.S.A. Department of Natural Sciences, Assumption College, Worcester, MA 01609, U.S.A. 3 Department of Physics and Astronomy, Tufts University, Medford, MA 02155, U.S.A. * indicates corresponding author: [email protected]; [email protected] 2

ABSTRACT We present a hybrid structure of Isotactic Polypropylene (iPP) nanocomposite with multiwall carbon nanotubes (MWCNTs). The polymer component contributes to the optical properties, flexibility and integrity of the polymer film while the carbon nanotubes change the thermal and mechanical stability, electrical and thermal conductivity and sensitivity. The multifunctional characteristics of this nanocomposite material are enhanced by anisotropic organization of the nanotubes and polymer through melt shearing which provides organization of the structural constituents at the molecular, nano, and micro length scales. This results in anisotropy of the macroscopic composite film properties parallel and perpendicular to the direction of shearing. On the molecular scale, the CNTs control the arrangement of the polymer molecules in a crystal lattice. On the nanometer scale, the CNTs couple to and align with the smectic normal of the liquid crystal phase of iPP. On the micron scale and larger, the secondary polymer crystal structure is rearranged due to the pinning of the polymer at the CNT surface to form fibrillar rather than spherulitic structures. These multi-scale rearrangements affect the optical, thermal, electrical, mechanical and chemical properties of the nanocomposite film. Our findings indicate that the CNTs under shear induce a novel anisotropy to the various thermo-physical properties of the iPP/CNTs films. We introduce an approach to extract the shear induced orientational order from the thermal conductivity of the dispersed CNTs. The index of refraction of the nanocomposites was also estimated via ellipsometry and was found to decrease slightly when CNTs were added and also showed shear induced anisotropy. The comparison between the results from the different experiments methods for probing induced anisotropy by melt shearing shows that orientation in iPP/CNTs nanocomposites induces anisotropy in multiple macroscopic properties. INTRODUCTION The history of human technology has been substitution of machines with materials that can do their function much more efficiently and without much maintenance. Natural fibers and materials have continuously been replaced with engineered, robust and versatile polymer-based single and multi-component materials. As such, the need for polymer-based materials that can respond to environment stimuli, classified as intelligent materials, is increasing by the day. In this work, we combine a polymer with carbon nanotubes. Polymers are excellent thermal and electrical insulators, while carbon nanotubes

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