title: Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites.
abstract: Polymer nanocomposites-materials in which a polymer matrix is blended with nanoparticles (or fillers)-strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently.
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: H Samet
authors.initials: HS
authors.lastname: Varol
authors.affiliation: Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
authors.forename: Fanlong
authors.initials: F
authors.lastname: Meng
authors.affiliation: SKF Engineering & Research Center, 3430DT Nieuwegein, The Netherlands.
authors.forename: Babak
authors.initials: B
authors.lastname: Hosseinkhani
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Malm
authors.affiliation: Institute of Physics, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bonn
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.affiliation: Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.|Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom.
authors.forename: Alessio
authors.initials: A
authors.lastname: Zaccone
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, 55128 Mainz, Germany; parekh@mpip-mainz.mpg.de.
authors.forename: Sapun H
authors.identifier: 0000-0001-8522-1854
authors.initials: SH
authors.lastname: Parekh
keywords: nanocomposites; nonlinear elasticity; polymer bridging; polymer chain alignment; strain stiffening