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ORDERING OF NANOPARTICLES MEDIATED BY END-FUNCTIONALIZED TRIBLOCK COPOLYMERS

ORDERING OF NANOPARTICLES MEDIATED BY END-FUNCTIONALIZED TRIBLOCK COPOLYMERS. Rastko Sknepnek , 1 Joshua Anderson, 1 Monica Lamm, 2 Joerg Schmalian, 1 and Alex Travesset 1. 1 Department of Physics and Astronomy and 2 Department of Chemical and Biological Engineering

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ORDERING OF NANOPARTICLES MEDIATED BY END-FUNCTIONALIZED TRIBLOCK COPOLYMERS

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  1. ORDERING OF NANOPARTICLES MEDIATED BY END-FUNCTIONALIZED TRIBLOCK COPOLYMERS Rastko Sknepnek,1 Joshua Anderson,1 Monica Lamm,2Joerg Schmalian,1 and Alex Travesset1 1Department of Physics and Astronomy and 2Department of Chemical and Biological Engineering Iowa State University and DOE Ames Laboratory Supported by U.S. Department of Energy Grant DE-AC02-07CH11358 AIChE meeting Philadelphia November 18, 2008 1/12

  2. Motivation Growing need to control material properties at nanometer length scales. Assemble nanoparticles into ordered structures. • simple and robust approach • sufficiently versatile Use block copolymers to guide nanoparticle assembly • self-assemble at nano scales • widely available • relatively easy to manipulate Pluronic®triblock copolymer: (Wanka, et al. Macromolecules 27, 4145 (1994)) AIChE meeting Philadelphia November 18, 2008 2/12

  3. Attach functional groups with affinity for nanoparticles nanoparticle Can functionalized triblocks be used to guide self-assembly of nanoparticles? coarse grain AIChE meeting Philadelphia November 18, 2008 3/12

  4. Model Nanoparticle Copolymer (CA5B7A5C) Fully flexible bead-spring chain. Minimal energy cluster of Nnp Lennard-Jones particles (Sloane, et al. Discrete Computational Geom. 1995) 7 hydrophobic (B) 1.2Rg 2.1Rg 2.5Rg 12 hydrophilic (A) 2 functional (C) Nnp=13 Nnp=55 Nnp=75 radius of gyration Rg=2.3s Non-bonded interactions (implicit solvent): Nanoparticle affinity eN is only tunable parameter! (set s=1, e=1, m=1) AIChE meeting Philadelphia November 18, 2008 4/12

  5. Simulation details LAMMPS – S. Plimpton, J. Comp. Phys. 117, 1 (1995) (lammps.sandia.gov) Each simulated system contains: HOOMD – J. Anderson, et al. J. Comp. Phys. 227, 5342 (www.ameslab.gov/hoomd) • p = 600 copolymer chains • n = 40 – 270 nanoparticles of size Nnp=13(1.2Rg), 55(2.1Rg), 75(2.5Rg) • all nanoparticles in a given system are monodisperse Explore phase diagram as a function of: • nanoparticle affinity eN (eN/kBT= 1.0, 1.5, 2.0, 2.5, 3.0) • packing fraction (f = 0.15, 0.20, 0.25, 0.30, 0.35) • NVT ensemble • reduced temperature T = 1.2 • harmonic bonds, k=330es-2, r0=0.9s • time step Dt = 0.005t (t=(ms2/e)1/2) • 107 time steps • relative nanoparticle concentration (c = 0.09, 0.12, 0.146, 0.17, 0.193, 0.215, 0.235) AIChE meeting Philadelphia November 18, 2008 5/12

  6. Results Sknepneket al., ACS Nano2, 1259 (2008) 1.2Rg A very rich phase diagram. Square columnar order is fully suppressed and novel 3D layered hexagonal order appears. Two-dimensional square columnar order dominates phase diagram. Square columnar order yields to 2D hexagonal columnar and 3D gyroid order. eN/kBT f f f nanoparticle concentration 18% 23% 10% AIChE meeting Philadelphia November 18, 2008 6/12

  7. Unconventional square columnar ordering 1.2Rg square columnar 10% 18% gyroid square columnar micellar liquid micellar liquid eN/kBT hexagonal columnar cylindrical mix disordered cylinders f f (top view) 9.5s hydrophilic hydrophobic functional nanoparticle AIChE meeting Philadelphia November 18, 2008 7/12

  8. Hexagonal ordering 1.2Rg layered hexagonal square columnar 18% 23% gyroid gyroid micellar liquid micellar liquid eN/kBT hexagonal columnar hexagonal columnar f f (top view) hydrophilic 11.5s hydrophobic functional (Toth, Regular figures, 1964) nanoparticle AIChE meeting Philadelphia November 18, 2008 8/12

  9. Extended region of gyroid ordering 1.2Rg layered hexagonal 18% 23% square columnar gyroid gyroid micellar liquid micellar liquid eN/kBT hexagonal columnar hexagonal columnar f f • gyroid order confirmed by structure factor • order shows Ia3d symmetry hydrophilic hydrophobic functional nanoparticle AIChE meeting Philadelphia November 18, 2008 9/12

  10. Layered hexagonal ordering 1.2Rg (top view) layered hexagonal 23% gyroid micellar liquid eN/kBT hexagonal columnar f simple hexagonal lattice (top view) (side view) hydrophilic hydrophobic honeycomb-like layers layered structure functional nanoparticle AIChE meeting Philadelphia November 18, 2008 10/12

  11. Cubic (CsCl) ordering 21% gyroid cubic (CsCl) 2.5Rg micellar liquid eN/kBT square columnar f (square columnar, top view) hydrophilic hydrophobic functional (cubic) nanoparticle AIChE meeting Philadelphia November 18, 2008 11/12

  12. Summary and Conclusions End-functionalized block copolymers are shown to provide an efficient strategy for assembly of nanocomposite materials. • a rich phase diagram • unconventional square columnar ordering • enhanced stability of gyroid phase eN/kBT f Sknepneket al., ACS Nano2, 1259 (2008) AIChE meeting Philadelphia November 18, 2008 12/12

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