Particle Characterization Needs –A Nanocomposite Perspective

Dr. Lee A. Silverman

DuPont Nanocomposite Technologies, Central Research and Development

Wilmington, Delaware 19880

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Textured Surfaces: (Physically Patterned or textured on the nanoscale)

Levels of Nanoscale

Design

Surface Films(Nanoscale in surface thickness only)

Nano Particles(nanoscale in one or more dimensions)

50 nm50 nm

Nanodevices

Nanostructured bulk materials(nanoscale internal structure)

Partitioning Nanotechnology Space

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Nanomaterials – An Enabling Technology

Manipulation of materials on very fine scale is broadly useful across polymer platforms

Desired property combinations can be achieved with proper selection of materials and microstructure

Examples• Rheology and mechanical

• Barrier and optical

• Thermal and surface roughness

Rheological

Optica

l

Electrical

Therm

al

Surf

ace

Barrier

ElectronicM

echanical

Unique Unique CombinationsCombinations

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Particle Dimensionality Defines Properties

plates

rods

spheres

Barrier, thermomechanical, flame retardancy, CTE in plane, very high interfacial area

electrical conductivity, themomechanical, network structures, fillers for fibers

Isotropy, transparency, electronic, magnetic, photonic, model systems

Properties/uses

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Nanoparticles Polymers

Polyimide

Fluoropolymers

Thermoset

Polyamide

Polyester

Polyolefins

Ionomers

Others…

Dispersion & Compatibilization

TiO2, SiO2, BaTiO3, AlN, diamonds, Q-dots, polymers…

CNT, Al2O3, SiC, TiO2tubes….

Clay, exfoliated graphite..

Interfacial Chemistry• Surfactants• Coupling agents

Structures & Interphase• Dendrimers• Multiblock polymers• Flexible links

Process Technology• Polymer processing• Milling/grinding• Particle

formation/modification

Nanocomposite Systems Require Compatible Particles, Polymers and Processes

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High Loadings Complicate Characterization

Silica in polystyrene (10%)

0.0

0.5

1.0

1.5

2.0

2.5

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

q (1/A)

S(q)

50 v% 40 v% 30 v% 20 v% 10 v%

SAXS Data

Fits hard sphere model

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Nielsen Model Relates Diffusion Barrier to Filler Aspect Ratio

Aspect Ratio = 25Aspect Ratio = 100Aspect Ratio = 200Aspect Ratio = 500

Tortuous Path Model

After L.E. Nielsen, Journal of Macromolecular Science, Part A, 1 (1967) 929 - 942

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Garboczi Model Relates Percolation Threshold to Ellipsoid Aspect Ratio

Pc ≡ critical volume fraction for percolation

E.J. Garboczi, et. al., Physical Review E, 52 (1995) 819-828

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Graphene/Polystyrene Composite Electrical Conductivity

S. Stankovich, et. al., Nature 442 (2006) 282-286

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Gao Model Relates Thermal Conductivity vs. Aspect Ratio

L. Gao, et. al.,Chemical Physics Letters, 434 (2007) Pages 297-300

Volume fraction = 0.05Kp/Km = 1000Contact resistance = 0

Ke/K

m

25

20

15

10

5

010-3 10-2 10-1 100 101 102 103

Aspect Ratio

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Surlyn 8945 Ec/E0 vs. MMT modifier, Concentration & Ar (aligned)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0% 7.0% 8.0% 9.0% 10.0%Filler Concentration (wt %)

Rel

ativ

e M

odul

us E

c/E0

l/h = 100.0l/h = 30.0l/h = 20.08945/20A8945/6A8945/93ANeut./20ANeut./6A

Halpin-Tsai Composites Model Relates Elastic Modulus to Filler Aspect Ratio

A

BC

Model Prediction: A f=30

Model Prediction: Af=20Com

plet

e exf

oliat

ion

After J.C. Halpin, et. al.,Polymer Engineering and Science, 16 (1976) 344-352

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Environmental, Health and Safety, and Product Stewardship“All fiber types capable of depositing in the thorax are not alike in their pathogenic potential…

A complete characterization (i.e., dimensions, fiber number, mass, and aerodynamic diameter) of the fiber aerosol and retained dose is essential.”

• R. McClellan, et. al. – Regul Toxicol Pharmacol, 16 (1992) 321-64

“A robust structure/activity paradigm has emerged from (research on fibre toxicology) that highlights fibre length, thinness, and biopersistence as major factors in determining the pathogenicity of a fibre.”

• K. Donaldson, Crit. Rev. Toxicol. 39 (2009) 487-500

DuPont’s stewardship process requires extensive characterization

• www.nanoriskframework.com

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How Should We Determine Particle Size (<100nm)

Scanning Electron Microscopy (SEM)

RodsSpheresPlates

Dry/Solvent Dispersed CompositeMethod

Scanning Probe Microscopy (SPM)

Static Light Scattering (SLS)

Small Angle X-ray Scattering (SAXS)

Transmission Electron Microscopy (TEM)

Dynamic light scattering (DLS)

RodsSpheresPlates

= highly oriented

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PMMA/Clay Composite

5 v% clay in PMMA

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How Should We Determine Particle Size (<100nm)

Re-entrant

Multi-modal

FacetedDistri-bution

Surface Area (BET)

Scanning Electron Micr. (SEM)

RodSpherePlate

CompositeMethod

Scanning Probe Micr. (SPM)

Static Light Scattering (SLS)

Small Angle X-ray Scattering (SAXS)

Transmission Electron Micr. (TEM)

Dynamic light scattering (DLS)

= specially oriented

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SummaryParticle size, shape, distribution critical in nanocomposites

• Property entitlement• EHS and product stewardship

We know how to characterize monodisperse spherical systems!Characterization of platy and rod-like particles onerous at best

• Highly oriented systems• Low particle concentrations

Characterization almost impossible in composites• Size distributions (especially multimodal)• Faceted particles• Highly irregular particles (especially re-entrant shapes)• High loadings

Surface chemistry is very important also• But is the subject of another (lengthy) discussion