END-FUNCTIONALIZED TRIBLOCK COPOLYMERS AS A ROBUST TEMPLATE FOR ASSEMBLY OF NANOPARTICLES Rastko Sknepnek, 1 Joshua Anderson, 1 Monica Lamm, 2 Joerg Schmalian,

END-FUNCTIONALIZED TRIBLOCK END-FUNCTIONALIZED TRIBLOCK COPOLYMERS AS A ROBUST TEMPLATE COPOLYMERS AS A ROBUST TEMPLATE

FOR ASSEMBLY OF NANOPARTICLESFOR ASSEMBLY OF NANOPARTICLES

Rastko SknepnekRastko Sknepnek,,11 Joshua Anderson, Joshua Anderson,11 Monica Lamm, Monica Lamm,22 Joerg Schmalian,Joerg Schmalian,11 and Alex Travesset and Alex Travesset11

11Department of Physics and Astronomy andDepartment of Physics and Astronomy and22Department of Chemical and Biological EngineeringDepartment of Chemical and Biological EngineeringIowa State University and DOE Ames LaboratoryIowa State University and DOE Ames Laboratory

APS March Meeting 2008, New OrleansAPS March Meeting 2008, New Orleans March 10, 2008March 10, 2008 1/11

APS March Meeting 2008, New OrleansAPS March Meeting 2008, New Orleans March 10, 2008March 10, 2008

MotivationMotivation

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• Growing need for complex materials with control of structure and properties Growing need for complex materials with control of structure and properties on on nanometer length scalesnanometer length scales..• Need for a Need for a simplesimple, “single-pass”, but , “single-pass”, but robustrobust fabrication technique. fabrication technique.

Our approachOur approach

Nanoparticle self-assembly via end-functionalized block copolymers.Nanoparticle self-assembly via end-functionalized block copolymers.

• Experimental results:Experimental results:• successful functionalizing of Pluronicsuccessful functionalizing of Pluronic®® triblock copolymers triblock copolymers• successful assembly of calcium phosphate nanocomposites successful assembly of calcium phosphate nanocomposites

• Limited theoretical understanding of self-Limited theoretical understanding of self-assembly of nanoparticle/copolymer assembly of nanoparticle/copolymer composites, especially in solution. composites, especially in solution.

Develop an understanding of mechanisms that lead to successful assemblyDevelop an understanding of mechanisms that lead to successful assemblynanocomposite materials.nanocomposite materials.

CH2

CH2

OCH

CH3

CH2 65

100

O OCH2

CH2

100

CH2

CH2

C O N

O

CON

O

HH peptide

peptide


ModelModel Simple coarse-grained bead spring model with implicit solvent.Simple coarse-grained bead spring model with implicit solvent.

Copolymer (Copolymer (CCAA55BB77AA55CC)) NanoparticleNanoparticle

12 hydrophilic12 hydrophilic(A)(A)

7 hydrophobic7 hydrophobic(B) (B)

Fully flexible bead-spring chain.Fully flexible bead-spring chain. Minimal energy cluster of NMinimal energy cluster of Nnpnp Lennard-Jones Lennard-Jones

particles (particles (Sloane, et al. Discrete Computational Geom. 1995Sloane, et al. Discrete Computational Geom. 1995))

2 functional2 functional(C)(C) NNnpnp=13=13 NNnpnp=55=55 NNnpnp=75=75

s

radius of gyration Rradius of gyration Rgg=2.3=2.3ss

2.1R2.1Rgg 2.5R2.5Rgg1.2R1.2Rgg

Non-bonded interactions:Non-bonded interactions:

12

4

r

rUs

612

4rr

rUss

12

4

r

rUs

612

4rr

rU N

ss

Nanoparticle affinity Nanoparticle affinity NN is only is only

tunable parameter!tunable parameter!(set (set ss=1, =1, =1, m=1)=1, m=1)

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Simulation detailsSimulation details Molecular dynamics using LAMMPS.Molecular dynamics using LAMMPS.LAMMPS – S. Plimpton, J. Comp. Phys. 117, 1 (1995)

(lammps.sandia.gov)

Explore phase diagram as a function of:Explore phase diagram as a function of:

• nanoparticle affinity nanoparticle affinity NN

612

4rr

rU N

ss((NN/k/kBBTT = 1.0, 1.5, 2.0, 2.5, 3.0)= 1.0, 1.5, 2.0, 2.5, 3.0)

• packing fractionpacking fraction

3/6 s

L

pNnN polynp (( = 0.15, 0.20, 0.25, 0.30, 0.35) = 0.15, 0.20, 0.25, 0.30, 0.35)

Each simulated system contains:Each simulated system contains:• p = 600 copolymer chainsp = 600 copolymer chains• n = 40 – 270 nanoparticles of size Nn = 40 – 270 nanoparticles of size Nnpnp=13(1.2R=13(1.2Rgg), 55(2.1R), 55(2.1Rgg), 75(2.5R), 75(2.5Rgg))• all nanoparticles in a given system are monodisperse all nanoparticles in a given system are monodisperse

• relative nanoparticle concentration relative nanoparticle concentration

polynp

np

pNnN

nNc

((cc = 0.09, 0.12, 0.146, 0.17, = 0.09, 0.12, 0.146, 0.17,

0.193, 0.215, 0.235)0.193, 0.215, 0.235)

• NVT ensemble NVT ensemble

• reduced temperature T = 1.2reduced temperature T = 1.2

• harmonic bonds, k=330harmonic bonds, k=330ss-2-2, , rr00=0.9=0.9ss

• time step time step t = t = 0.0050.005mmss

• 10107 7 time stepstime steps4/11

ResultsResults Phase diagrams for NPhase diagrams for Nnpnp=13 (1.2R=13 (1.2Rgg))

nanoparticlenanoparticle concentrationconcentration

10%10% 18%18% 23%23%APS March Meeting 2008, New OrleansAPS March Meeting 2008, New Orleans March 10, 2008March 10, 2008

Depending on the relative nanopaticle concentration one observes a large number Depending on the relative nanopaticle concentration one observes a large number of two- and three-dimensional periodic ordered structures .of two- and three-dimensional periodic ordered structures .

Two-dimensional Two-dimensional square square columnarcolumnar order order

dominates phase dominates phase diagram. diagram.

Square columnar Square columnar order yields to 2D order yields to 2D

hexagonal columnarhexagonal columnar and 3D and 3D gyroidgyroid order. order.

Square columnar Square columnar order is fully order is fully

suppressed and suppressed and novel 3D novel 3D layered layered hexagonalhexagonal order order

appears. appears.

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1.2R1.2Rgg

ResultsResults


Square columnar ordering, NSquare columnar ordering, Nnpnp=13 (1.2R=13 (1.2Rgg))

10% 18%

hydrophilichydrophilichydrophobichydrophobicfunctionalfunctionalnanoparticlenanoparticle

Geometric interpretationGeometric interpretation

(Toth, (Toth, Regular figuresRegular figures, 1964), 1964)

• dominates phase diagram dominates phase diagram for small NP concentration for small NP concentration

(top view)(top view)

• two-dimensional ordertwo-dimensional order• two interpenetrating two interpenetrating “line-lattices” with lattice “line-lattices” with lattice constant 9.5constant 9.5ss..

9.59.5ss

• closely related to the closely related to the problem of close problem of close packing of binary diskspacking of binary disks

size ratio = 0.414214size ratio = 0.414214concentration = 1/2concentration = 1/2

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1.2R1.2Rgg

square square columnar columnar micellarmicellar

liquidliquid

gyroidgyroid

hexagonal hexagonal columnarcolumnar

micellarmicellarliquidliquid

NN/k/k

BBTT

square square columnar columnar

cylindricalmix

disordered disordered cylinders cylinders

ResultsResults Hexagonal columnar ordering, NHexagonal columnar ordering, Nnpnp=13 (1.2R=13 (1.2Rgg))

18% 23%



(top view)(top view)

(Toth, (Toth, Regular figuresRegular figures, 1964), 1964)

size ratio = 0.349198size ratio = 0.349198concentration = 6/7concentration = 6/7

Geometric interpretationGeometric interpretation

11.511.5ss

• closely related to the closely related to the problem of close problem of close packing of binary diskspacking of binary disks

• two-dimensional ordertwo-dimensional order• micelles form two-micelles form two-dimensional “line-lattice” dimensional “line-lattice” with lattice constant 11.5with lattice constant 11.5ss• nanoparticles fill space in nanoparticles fill space in betweenbetween

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1.2R1.2Rgg



gyroidgyroidlayered layered

hexagonal hexagonal gyroidgyroidsquare square

columnar columnar

NN/k/k

BBTT



ResultsResults Gyroid ordering, NGyroid ordering, Nnpnp=13 (1.2R=13 (1.2Rgg))


18% 23%


• gyroid order confirmed gyroid order confirmed by structure factor by structure factor • order possess Ia3d order possess Ia3d symmetrysymmetry

• three-dimensional orderthree-dimensional order• micelles and nanoparticles micelles and nanoparticles form two interpenetrating form two interpenetrating gyroidsgyroids• fully connected triply fully connected triply periodic structures periodic structures • nanoparticles stabilize nanoparticles stabilize gyroid over a wide parameter gyroid over a wide parameter rangerange

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1.2R1.2Rgg


hexagonal hexagonal columnar columnar



gyroidgyroidgyroidgyroid

NN/k/k

BBTT


layered layered hexagonal hexagonal

ResultsResults Layered hexagonal ordering, NLayered hexagonal ordering, Nnpnp=13 (1.2R=13 (1.2Rgg))


23%

(top view)(top view) (top view)(top view) (side view)(side view)


simple hexagonalsimple hexagonal latticelattice

honeycomb-like honeycomb-like layerslayers

layered structurelayered structure

• three-dimensional layered ordered structurethree-dimensional layered ordered structure• spherical micelles form simple hexagonal latticespherical micelles form simple hexagonal lattice• nanoparticles form layers that resemble honeycombnanoparticles form layers that resemble honeycomb• each nanoparticle layer is stacked between two each nanoparticle layer is stacked between two micellar layers and vice verse. micellar layers and vice verse.

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1.2R1.2Rgg

NN/k/k

BBTT

layered layered hexagonal hexagonal



gyroidgyroid

ResultsResults Cubic (CuCl) and square columnar orderings, NCubic (CuCl) and square columnar orderings, Nnpnp=75 (2.5R=75 (2.5Rgg))


21%

hydrophilichydrophilichydrophobichydrophobicfunctionalfunctionalnanoparticlenanoparticle (cubic)(cubic)

(square columnar, top view)(square columnar, top view)

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• spherical micelles and nanoparticles form spherical micelles and nanoparticles form two simple cubic latticestwo simple cubic lattices• cubic lattices are shifted by (a/2,a/2,a/2) cubic lattices are shifted by (a/2,a/2,a/2) with respect to each other forming a CuCl with respect to each other forming a CuCl structurestructure• low packing fraction low packing fraction non-trivial non-trivial interaction effects interaction effects

2.5R2.5Rggmicellarmicellarliquidliquid

gyroidgyroid


cubic (CuCl)cubic (CuCl)

Summary and ConclusionsSummary and Conclusions

APS March Meeting 2008, New OrleansAPS March Meeting 2008, New Orleans March 10, 2008March 10, 2008 11/11

• Used a simple coarse grained model to study Used a simple coarse grained model to study nanoparticle self-assemblynanoparticle self-assembly mediated by end-functionalized triblock copolymers.mediated by end-functionalized triblock copolymers.• Extensively studied phase diagram of the nanocomposite system as function Extensively studied phase diagram of the nanocomposite system as function of nanoparticle size, concentration and affinity for copolymer functional ends.of nanoparticle size, concentration and affinity for copolymer functional ends.

• Showed that end-functionalized triblock copolymer can provide a simple, but Showed that end-functionalized triblock copolymer can provide a simple, but powerful strategy for assembling nanocomposite materialspowerful strategy for assembling nanocomposite materials

• very rich phase diagram with five distinct two- and three-dimensional very rich phase diagram with five distinct two- and three-dimensional ordered structuresordered structures• each ordered structure has unique and rich propertieseach ordered structure has unique and rich properties• easy to tune between ordered structures by changing, e.g., easy to tune between ordered structures by changing, e.g., nanoparticle concentration nanoparticle concentration

End-functionalized block copolymers are End-functionalized block copolymers are shown to provide an efficient strategy for shown to provide an efficient strategy for assembly of nanocomposite materials. assembly of nanocomposite materials.

Documents

END-FUNCTIONALIZED TRIBLOCK COPOLYMERS AS A ROBUST TEMPLATE FOR ASSEMBLY OF NANOPARTICLES Rastko Sknepnek, 1 Joshua Anderson, 1 Monica Lamm, 2 Joerg Schmalian,