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Mechanical Properties of Nanocomposites

Mechanical Properties of Nanocomposites. John Rozen Chem 350. Outline. Mechanical Properties of Materials Polymers and Nanotubes Properties of Nanocomposites Conclusion. Outline. Mechanical Properties of Materials Polymers and Nanotubes Properties of Nanocomposites Conclusion.

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Mechanical Properties of Nanocomposites

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  1. Mechanical Properties of Nanocomposites John Rozen Chem 350

  2. Outline • Mechanical Properties of Materials • Polymers and Nanotubes • Properties of Nanocomposites • Conclusion

  3. Outline • Mechanical Properties of Materials • Polymers and Nanotubes • Properties of Nanocomposites • Conclusion

  4. Mechanical Properties of Materials The stiffness : proportional to Young’s modulus which is the slope of the curve Stress-Strain experiment curve : elastic deformation plastic deformation breaking The strength : value of the stress when breaking → → → • The toughness : amount of absorbed energy given by the area under the curve

  5. Outline • Mechanical Properties of Materials • Polymers and Nanotubes • Properties of Nanocomposites • Conclusion

  6. Polymers Origin of elasticity : ► Energy minimized when straight ► Cannot reach equilibrium ► Creation of an amorphous phase ► Movements allowed

  7. Polymers • Creep-Recovery : ► A constant force is applied Fast elastic response Slow deformation processes ► Recovery shows constant damages → → • Energy relaxation processes in the amorphous phase : ►Elasticity is due to local movements of monomers which can freely rotate and increase the total extension of the chain in the amorphous phase. ► Irreversible deformationis the consequence of viscous flows occuring in the amorphous phase presents between crystallites .

  8. Nanotubes • Mechanical properties : ► High stiffness is expected (rolled graphite sheets) ► High axial strength is expected ► How to probe single tubes? • Transmission Electron Microscope measurements ► Young’s modulusof multi-walled nanotubes (MWNTs) is probed by analyzing the thermal vibrations in the tube. ► “Exceptionnally high stiffness” in the TPa range is detected. ► It is higher than usual carbon fibers but it drops to 15 Gpa in the bulk.

  9. Nanotubes The Nanomanipulator ► AFM as a tool ► Electron microscope for observation ► Feel the nanotubes ► Displace the nanotubes

  10. Nanotubes • Bending of a tube ►The AFM tip applies a lateral force ► Friction with substrate induce bending • Buckles ►Formed to reduce the stress ► Move with deformation and disappear → reversible & not defectrelated • Maximum stress ►Intact after repeated maximum stress → high strength Falvo et al., Nature 389, 582 (1997)

  11. Outline • Mechanical Properties of Materials • Polymers and Nanotubes • Properties of Nanocomposites • Conclusion

  12. Alumina & Nanotubes • Properties of ceramics : ►Low density ►Stiff and strong (even at high T) ►Low sensitivity to corrosion ►Very brittle (more than metals) • Mixing process : ► Ball-milling of powders → good dispersion ► Sintering to reduce pores sizes → fracture toughness Zhan et al., Nature Materials 2, 38 (2003)

  13. Alumina & Nanotubes • Resulting properties : ► Strength reduced ► Toughness multiplied by 3 → better than MW → better than Fe

  14. Polymers & Nanotubes • The homogeneity challenge ► How to overcome phase segregation? ► Florry-Huggins expression → ΔGmix = -TΔSt + ΔGloc → two distinct phases? • Mixing process : ► Layer by Layer (LBL) deposition → dipping in NT & PEI ► Heating of the material → induced covalent crosslinking → highest strength observed Mamedov et al., Nature Materials 1, 190 (2002)

  15. Outline • Mechanical Properties of Materials • Polymers and Nanotubes • Properties of Nanocomposites • Conclusion

  16. Conclusion • Every material has its own properties ► stiffness ► strength ► toughness • They can be mixed but there are concerns ► homogeneity ► load transfer • The resulting materials have enhanced properties ► their application range is widen

  17. Bibliography

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