title: Influence of three-dimensional nanoparticle branching on the Young's modulus of nanocomposites: Effect of interface orientation.
abstract: With the availability of nanoparticles with controlled size and shape, there has been renewed interest in the mechanical properties of polymer/nanoparticle blends. Despite the large number of theoretical studies, the effect of branching for nanofillers tens of nanometers in size on the elastic stiffness of these composite materials has received limited attention. Here, we examine the Young's modulus of nanocomposites based on a common block copolymer (BCP) blended with linear nanorods and nanoscale tetrapod Quantum Dots (tQDs), in electrospun fibers and thin films. We use a phenomenological lattice spring model (LSM) as a guide in understanding the changes in the Young's modulus of such composites as a function of filler shape. Reasonable agreement is achieved between the LSM and the experimental results for both nanoparticle shapes--with only a few key physical assumptions in both films and fibers--providing insight into the design of new nanocomposites and assisting in the development of a qualitative mechanistic understanding of their properties. The tQDs impart the greatest improvements, enhancing the Young's modulus by a factor of 2.5 at 20 wt.%. This is 1.5 times higher than identical composites containing nanorods. An unexpected finding from the simulations is that both the orientation of the nanoscale filler and the orientation of X-type covalent bonds at the nanoparticle-ligand interface are important for optimizing the mechanical properties of the nanocomposites. The tQD provides an orientational optimization of the interfacial and filler bonds arising from its three-dimensional branched shape unseen before in nanocomposites with inorganic nanofillers.
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Departments of Materials Science and Engineering.
authors.forename: Shilpa N
authors.initials: SN
authors.lastname: Raja
authors.affiliation: Chemistry.
authors.forename: Andrew C K
authors.initials: AC
authors.lastname: Olson
authors.affiliation: Chemical Engineering, and.
authors.forename: Aditya
authors.initials: A
authors.lastname: Limaye
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Departments of Materials Science and Engineering.
authors.forename: Kari
authors.initials: K
authors.lastname: Thorkelsson
authors.affiliation: Chemical Engineering, and.
authors.forename: Andrew
authors.initials: A
authors.lastname: Luong
authors.affiliation: Mechanical Engineering, University of California, Berkeley, CA 94720; and.
authors.forename: Liwei
authors.initials: L
authors.lastname: Lin
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Departments of Materials Science and Engineering, Mechanical Engineering, University of California, Berkeley, CA 94720; and.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Ritchie
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Departments of Materials Science and Engineering, Chemistry.
authors.forename: Ting
authors.initials: T
authors.lastname: Xu
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Departments of Materials Science and Engineering, Chemical Engineering, and Kavli Energy NanoScience Institute, Berkeley, CA 94720 APAlivisatos@lbl.gov.
authors.forename: A Paul
authors.initials: AP
authors.lastname: Alivisatos
keywords: lattice spring model; nanocomposite films; polymer fibers; tetrapod quantum dot; three-dimensional nanoparticle branching