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Irradiation-induced stiffening of carbon nanotube bundles

Irradiation-induced stiffening of carbon nanotube bundles. Maria Sammalkorpi (née Huhtala) 1 , Arkady Krasheninnikov 2 , Antti Kuronen 1 , Jussi Aittoniemi 1 , Kai Nordlund 2 , Steve Stuart 3 , Kimmo Kaski 1 1 Laboratory of Computational Engineering, Helsinki University of Technology

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Irradiation-induced stiffening of carbon nanotube bundles

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  1. Irradiation-induced stiffening of carbon nanotube bundles Maria Sammalkorpi (née Huhtala)1, Arkady Krasheninnikov2, Antti Kuronen1, Jussi Aittoniemi1, Kai Nordlund2, Steve Stuart3, Kimmo Kaski1 1Laboratory of Computational Engineering, Helsinki University of Technology 2Accelerator Laboratory, University of Helsinki 3Department of Chemistry, Clemson University Cosires 2004 Helsinki June 28th – July 2nd

  2. Outline • Introduction • Irradiation as a means of tailoring carbon nanotube (CNT) and nanotube bundle properties • Irradiation effects in nanotubes • Load transfer in multi-walled nanotubes • Nanotube bundle stiffening • Summary Cosires 2004 Helsinki June 28th – July 2nd

  3. Introduction: carbon nanotubes (CNTs) • Tubular carbon molecules • Strong covalent intra-tube bonding • Outstanding axial tensile strength & Young’s modulus • Weak van der Waals inter-tube bonding • Ultra-low friction surfaces • Ideal candidates for reinforcement fibres in composites • Problem: low shear Cosires 2004 Helsinki June 28th – July 2nd

  4. Improve load transfer? Vacancies axial weakening vacancy-vacancy covalent bond formation [1] Interstitials inside and between tubes mobile dimerization [1] R. Telling et al., Nat. Mat. 2, 333 (2003). Simulation: MD with Brenner C-C interaction with long range van der Waals extension by Stuart et al. Irradiation and nanotubes Cosires 2004 Helsinki June 28th – July 2nd

  5. Caused by vacancies Young’s modulus: Y0 intact tube Young’s modulus ni defect concentration aYi coefficients Fitted aYi values Concentration must be high to reduce Y Irradiation induced structural weakening Cosires 2004 Helsinki June 28th – July 2nd

  6. Structural weakening: Tensile strength Cosires 2004 Helsinki June 28th – July 2nd

  7. Load transfer • Can irradiation defects improve the load transfer? • Setup: What is the minimum force required to pull out the inner tube? • Contributions • capillary force • tube-tube shear equal at L~200nm • defects Cosires 2004 Helsinki June 28th – July 2nd

  8. Force: defect-free nanotubes • Short (36Å) commensurate / incommensurate tube being pulled out from a longer one (62Å), at T=0K • At room temperature t~0.1MPa Cosires 2004 Helsinki June 28th – July 2nd

  9. Tubes with defects • Single vacancies reconstruct to protrude a dangling bond 0.5-0.7Å out of plane [1] • Two vacancies in adjanced planes of graphite can form a covalent bond [2] • Interstitials are mobile in room temperature • Model: metastable covalent configurations [1] El-Barbary et al., PRB 68, 144107 (2003). [2] R. Telling et al., Nature Materials 2, 333 (2003). Cosires 2004 Helsinki June 28th – July 2nd

  10. Tubes with defects One vacancy (not covalent) Two vacancies Interlayer interstitial Interlayer dimer Cosires 2004 Helsinki June 28th – July 2nd

  11. Inter-shell bond strength: results • Non-covalent bonding strength 0.1-0.4nN (vacancy) • Covalent bonding strength 4-8nN (2-vacancy) • Defects dominate at (D=6nm, L=500nm CNT) • 10-6Å-2 (~1/300nm, ~5x1017cm-3) for covalent binding • 10-5Å-2 (~1/10nm, ~2x1019cm-3) for non-covalent binding • Defects in nanotubes are realistic means for load transfer Cosires 2004 Helsinki June 28th – July 2nd

  12. Nanotube bundle stiffening • Ref. [1]: electron irradiation of bundles of single-walled carbon nanotubes (SWNTs) result in • (1) dramatic increase of the bundle bending modulus • (2) followed by a decrease at higher doses • What is the reason for this nonlinear behavior? [1] Kís et al., Nature Materials 3, 153 (2004). Cosires 2004 Helsinki June 28th – July 2nd

  13. Bending modulus • Bundle = cylindrical macroscopic bar • Bending modulus • Simulations: Y,G • Y~vacancies • G~covalent inter-tube bonds • YB Cosires 2004 Helsinki June 28th – July 2nd

  14. aY = 1.2Å Y0 = 370GPa (uniformly loaded bulk bundle) G = aG nbonds aG = 14.5 N/m Young’s and shear modulus:(5,5)-bundle Cosires 2004 Helsinki June 28th – July 2nd

  15. Bending modulus • Analytical approximations[1] • Cross section • Number of secondary cascade atoms • Nvac(dose, E) • Nbonds(Nvac,interaction area) • Y,G as a function of dose and E • YB [1] F. Banhart, Rep. Prog. Phys. 62, 1181 (1999). Cosires 2004 Helsinki June 28th – July 2nd

  16. Summary • Y only moderately sensive (-3% for 1/50Å density (5,5)) • Tensile strength may decrease by 50% • reconstruction improves strength • Irradiation induced defects pin CNTs effectively • 10-6Å-2 (covalent), 10-5Å-2 (non-covalent) • Preliminary results for bundle bending modulus • Increase and followed by decrease due to interplay between • 1) Increased shear via inter-tube bonds • 2) Degrade of strength due to vacancies • Overestimate of max YB, Y0 too large? • Irradiation good tool to improve nanotube mechanical properties for usage as reinforcement agents [1] M. Sammalkorpi et al, submitted., [2] M. Huhtala et al, PRB 70, ?? (2004). [1] [2] Cosires 2004 Helsinki June 28th – July 2nd

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