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Nanoparticle Phenomena

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Nanoparticle Phenomena D. Huitink 4/7/09 Overview Why nanoparticles? How does shape affect properties? Results of Nanocomposite materials Discussion of Shape ... – PowerPoint PPT presentation

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Title: Nanoparticle Phenomena


1
Nanoparticle Phenomena
  • D. Huitink 4/7/09

2
Overview
  • Why nanoparticles?
  • How does shape affect properties?
  • Results of Nanocomposite materials
  • Discussion of Shape formation

3
NanoWhats the Big Deal?
  • Nanoparticle object with at least one dimension
    smaller than 100nm
  • Huge theoretical property enhancement
  • Measurements agree
  • Can be adapted into composite materials for
    enhanced characteristics

4
Does Size Matter?
  • Surface area to Volume ratio
  • Move away from body forces toward surface and
    chemical interactions
  • For a fixed volume particle, shape also affects
    these features

5
Nanoparticle Properties
K. Dick, T. Dhanasekaran, Z. Xhang and D. Meisel,
J. Am. Chem. Soc, 2002, 124(10), 2312
6
Nanoparticle Properties
R.W. Siegel, Scientific American, December 1996,
42 Y.Y. Lim and M.M. Chaudhri, Philos. Mag.A,
2002, 82(10), 2071
7
Effects in Composite Materials
Sorbitol without Au NPs
Sorbitol Ø55nm Au NPs
8
Surface Properties
9
Bulk Properties
Schematic of 3 Point Bending Test
F
Sample Flexural Modulus
Sorbitol only 0.173 GPa 0.03
Sorbitol Gold nanorods (Ø40nm x 300nm) 0.055 GPa 0.015
Sorbitol spherical Gold nanoparticles (Ø55nm) 0.108 GPa 0.042
L/2
L/2
Ø

d
EFL3/12pR4


F/d
  • increased surface area affected the flexural
    stiffness more
  • poor adhesion of Au NPs with sorbitol
  • shrinkage effect
  • reduced load bearing ability

10
Can the properties be designed?
  • Can we control size and shape precisely?
  • Classical nucleation process theories suggest no,
    but experiments show otherwise
  • But not perfected, yet
  • Can the process be modeled more accurately?

11
Nano-Thermodynamics
Free Energy
G1
G2
Metastable State 1
Stable State 2
State/Configuration
12
TEM images courtesy of S. Kundu
13
How to reduce ?se?
  • Surface energy is results from
  • unpaired bonds (ionic, etc)
  • Vacant lattice sites (metallic, etc)
  • Macroscale reduction by oxidation, etc
  • Same at nanoscale, just needs a little extra
    motivation surface passivation by chemicals

14
What about modeling?
  • How is shape related to process parameters?
  • Crystal structure FCC, BCC, HCP
  • Defines growth directions
  • 2) Surface relaxation due to surfactant ordering

Balluffi, R. Kinetics of Materials. 2005 p461
15
What is driving force?
  • Possibilities
  • Concentration limited flux of surfactant vs NP
    atoms
  • Surfactant primarily forms on first growth
    directions
  • 2) Surfactant molecule self-assembly
  • Eg. Natural attraction/repulsion
  • 3) Energetic ordering irradiation driven

16
What is driving force?
  • Edges/Corners have higher energy
  • May attract surfactant molecules in higher density

17
Concluding remarks
  • Nanomaterials have substantial effects on bulk
    composite properties
  • Shape and size dependent effects
  • Chemistry of Nanoparticles allows for unique size
    and shape
  • Isotropy is defined by concentrations and other
    process parameters

18
The Goal
  • To develop statistically sound methods of
    generating uniform particles
  • Characterize which parameters control what
    isotropic behavior
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