Dissertation presentation

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Dissertation presentation

• Nano-Particulate Dispersion and Reinforcement of
  Nanostructured Composite Materials
• by
• Virginia Hiu-Hung Yong
• Academic advisor Professor H. Thomas Hahn
• Dept. of Materials Science Engineering
• University of California, Los Angeles

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Publications

• Yong, V. and Hahn, H.T. Kevlar/vinyl ester
  composites with SiC nanoparticles, Proceedings
  of the 49th International SAMPE Symposium and
  Exhibition, Vol. 49, 2004, pp. 2399-2409.
• Yong, V. and Hahn, H.T. Processing and
  properties of SiC / vinyl ester nanocomposites,
  Nanotechnology, Vol. 15, No. 9, 2004, pp.
  1338-1343.
• Yong, V. and Hahn, H.T. Dispersant optimization
  using design of experiments for SiC/vinyl ester
  nanocomposites, Nanotechnology, Vol. 16, No. 4,
  2005, pp. 354-360.
• Yong, V. and Hahn, H.T. The effect of coupling
  agent / dispersant on rheology of SiC
  nanoparticle suspension in vinyl ester resin.
  In press.
• Yong, V. and Hahn, H.T. SiC/vinyl ester
  nanocomposites Dispersant formulation for
  enhanced mechanical properties. In
  preparation.

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Outline

• Objective, approach, and benefit
• Practical difficulties
• Results (Ch.4)
• Processing and properties
• Design of experiments
• Rheology
• Dispersant formulation
• Conclusions
• Question Answer

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Dissertation

• Objective
• Enhance performance by adding nanoreinforcements
• Approach
• Develop methods for full dispersion of SiC
  nanoparticles
• Assess properties of SiC/vinyl ester
  nanocomposites
• State of the Art
• Availability of functional nanoparticles
• Benefit
• Enhanced performance for multifunctional
  nanostructures

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Practical difficulties

• Particles lt 1 ?m van der Waals, Coulombic and
  other cohesive forces
• Dispersion
• Viscosity

Figure 1. Viscosity vs. SiC for micron- and
nano-particles.
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Processing and properties - Processing 1

• Gamma-methacryloxy propyl trimethoxy silane (MPS)
  was chosen as the coupling agent. FT-IR was used
  to study the silanol condensation between MPS and
  the SiC nanoparticles.

Figure 6. FT-IR spectra of SiC samples.
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Processing and properties - Processing 2

• Calculation of monolayer dose mf Parfitt
  (1981)
• ms mass of SiC nanoparticles 1 wt. of 15 ml
  of VE 0.156/1000 kg
• Asp specific surface area (30 nm SiC) 62500
  m2/kg
• Mf molar mass of MPS 248.4/1000 kg/mol
• Af molar area coverage ? 105 m2/mol this
  corresponds to 6 molecules
• adsorbed per nm2 (or 100 Å2) of surface.
• Vl volume of liquid (m3) CMCf saturated
  solubility, assume 0 mol/m3.
• MPS dosage (for 1 wt. SiC) 0.104 g 67 wt.
  of SiC
• Asp specific surface area (1 ?m SiC) 1875
  m2/kg
• Monolayer dose mf 0.466 wt. in agreement
  with guideline
• 1 3 wt. of SiC (? 4 monolayers) in 0.1
  3 ?m particle size range.

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Processing and properties - Properties 1

• Without dispersant - Ultrasonic mixing did not
  fully disperse the particles. As a result, the
  composite strength did not improve although the
  modulus increased.

Figure 11. Fractography of fracture surfaces of 1
vol. SiC samples.
Figure 10. Stress vs. strain curve of 0, 1, 2
vol. SiC without dispersant.
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Processing and properties - Properties 2

• The use of a dispersant MPS improved the
  dispersion quality and hence the composite
  strength.

Figure 8. Optical photographs at 100X of 1 vol.
SiC samples. (a) with MPS in situ mixing (b)
without dispersant.
Figure 10. Stress vs. strain curve of 0 , 1
vol. SiC with MPS via in situ addition.
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Design of experiments

• Objective determine optimum dosage of BYK-W 966
  and its interaction with MPS, to achieve maximum
  flexural strength.
• Factor 1 BYK-W 966 Factor 2 MPS
• 67 wt. BYK-W 966 (x1 0, x2 -1.414)
• 67 wt. MPS (done) (x1 -1.414, x2 0)
• 22 factorial design
• Response Surface Methodology (RSM)
• Central composite design
• nf 22 20 wt. (x -1), 114 wt. (x 1)
• nc 5 (uniform-precision rotatable) 67 wt. (x
  0)
• na 2 x 2 0 (x -1.414), 134 wt. (x 1.414)
• Blocking factor Day

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DOE1 Interaction plot
Figure 14. Interaction plot for Agglomerate
Size showing that MPSW966 interaction appears
significant.
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DOE1 Box plot
Figure 15. Box plot for Agglomerate Size
showing that both MPS and W966 improve
dispersion and reduce dispersion variation.
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DOE2 Overlay contour plot
Figure 27. An overlay contour plot.
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DOE2 Confirmation run

• At optimum setting (MPS and W966 at 67), 0.5
  wt. SiC resulted in 8 increase in strength and
  14 increase in modulus.

Figure 25. Prediction profile plot
simultaneous optimization of Agglomerate Size
and STRENGTH.
Figure 28. Stress vs. strain curve.
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DOE - Conclusions

• For coupling agent MPS, a good correlation was
  observed for the optimal dosage to achieve the
  maximum flexural strength and the best
  dispersion.
• For dispersant W966, the optimal dosage which
  gives the best dispersion doesnt achieve the
  maximum flexural properties.
• A strong filler/matrix interfacial bonding is of
  vital importance for achieving enhanced flexural
  properties.
• At optimum dosage of MPS and W966 (both at 67),
  a small amount of SiC in 0.5 wt. was able to
  increase the strength by almost 10 .
• The DOE2 results suggest an optimal dosage in a
  11 ratio, which is in agreement with the
  literature Cope (1979) .

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Rheology

• The rheological behavior of SiC
  nanoparticle-filled vinyl ester resin systems was
  evaluated using the Bingham, power law,
  Herschel-Bulkley, and Casson models.

Table 7. Summary of rheological behavior of
SiC/vinyl ester resin systems.
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Rheology - Dispersion characteristics

• A 50 decrease in suspension viscosity was
  observed at the optimal dispersant dosage for 3
  vol. SiC.

Figure 39 40. Rheological profiles showing
optimum dosage of (a) MPS/W966 (b) 1-octanol.
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Dispersant formulation- Characterization of SiC
surfaces

• The small 1100 1070 (Si-O stretching) and 3550
  3300 (O-H stretching) cm-1 band absorbance
  indicates that the degree of SiC surface
  oxidation is negligible.

Figure 41. FT-IR spectrum of as-received SiC
nanoparticles.
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Dispersant formulation - Schematic diagram
Figure 44. Schematic diagram of the design of
dispersants for SiC/vinyl ester nanocomposite
synthesis.
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Dispersant formulation - Flexural properties

• 3 vol. SiC resulted in 75 increase in modulus,
  42 increase in strength, and 75 increase in
  toughness.

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Dispersant formulation - Fracture analysis

• Fracture surfaces were devoid of any particle
  agglomerates.

(a)
(b)
Figure 46. Fracture initiation sites (a) with
dispersant mono-2- (methacryloyloxy)ethyl
succinate (b) without dispersant.
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Dispersant formulation- Dispersion
characterization 1
Figure 51. AFM image shows a full dispersion of
SiC (in 3 vol. ) in vinyl ester with
mono-2-(methacryloyloxy)ethyl succinate.
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Dispersant formulation- Dispersion
characterization 2
(a)
(b)
Figure 50 51. Particle dispersion as observed
on AFM (a) 1 vol. (b) 3 vol. SiC, with
mono-2-(methacryloyloxy)ethyl succinate.
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Summary 1
Figure 48. Effect of dispersants on strength.
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Summary 2
Figure 49. Effect of dispersants on modulus.
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Conclusions

• DOE results illustrate that a good dispersion
  coupling with a strong filler/matrix interfacial
  bonding is the key to obtain enhanced flexural
  properties.
• Rheology of SiC/VE systems was studied. For 3
  vol. SiC, a 50 decrease in suspension viscosity
  was achieved at the optimal dispersant dosage.
• A dispersant mono-2-(methacryloyloxy)ethyl
  succinate was formulated. When used in 3 vol.
  SiC/VE composite, this dispersant resulted in 75
  increase in modulus, 42 increase in strength,
  and 75 increase in toughness. Full dispersion
  of SiC was observed under AFM.
• The research shows that with good dispersion,
  nanoparticles will improve mechanical properties
  of nanocomposites. This opens doors to the
  utilization of functional nanoparticles in
  multifunctional applications.

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Acknowledgments

• We would like to thank
• the Air Force Office of Scientific Research (L.
  Lee) and the U.S. Army Natick Laboratory (J. Song
  and M. Sennett) for financial support through
  AFOSR Grant F49620-02-1-0414, and
• Dr. John W. Goodman for his advice.

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Question Answer

• Thank You