cosires 2004 helsinki june 28th – july 2nd irradiation-induced stiffening of carbon nanotube...
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Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Irradiation-induced stiffening Irradiation-induced stiffening of carbon nanotube bundlesof carbon nanotube bundles
Maria Sammalkorpi Maria Sammalkorpi (née Huhtala)(née Huhtala)11,,
Arkady KrasheninnikovArkady Krasheninnikov22, Antti Kuronen, Antti Kuronen11, Jussi Aittoniemi, Jussi Aittoniemi11, , Kai NordlundKai Nordlund22, Steve Stuart, Steve Stuart33, Kimmo Kaski, Kimmo Kaski11
11Laboratory of Computational Engineering, Helsinki University of TechnologyLaboratory of Computational Engineering, Helsinki University of Technology22Accelerator Laboratory, University of HelsinkiAccelerator Laboratory, University of Helsinki
33Department of Chemistry, Clemson UniversityDepartment of Chemistry, Clemson University
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
OutlineOutline
IntroductionIntroduction
Irradiation as a means of tailoring carbon Irradiation as a means of tailoring carbon nanotube (CNT) and nanotube bundle nanotube (CNT) and nanotube bundle propertiesproperties– Irradiation effects in nanotubesIrradiation effects in nanotubes– Load transfer in multi-walled nanotubesLoad transfer in multi-walled nanotubes– Nanotube bundle stiffeningNanotube bundle stiffening
SummarySummary
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Introduction: carbon nanotubes Introduction: carbon nanotubes (CNTs)(CNTs)
Tubular carbon moleculesTubular carbon molecules– StrongStrong covalent intra-tube covalent intra-tube
bonding bonding Outstanding axial tensile Outstanding axial tensile strength & Young’s strength & Young’s modulusmodulus
– WeakWeak van der Waals inter- van der Waals inter-tube bondingtube bonding
Ultra-low friction surfaces Ultra-low friction surfaces
Ideal candidates for Ideal candidates for reinforcement fibres in reinforcement fibres in compositescomposites– Problem: low shearProblem: low shear
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Irradiation and nanotubesIrradiation and nanotubes
Improve load transfer?Improve load transfer?
VacanciesVacancies– axial weakeningaxial weakening– vacancy-vacancy covalent vacancy-vacancy covalent
bond formation [1]bond formation [1]
InterstitialsInterstitials– inside and between tubesinside and between tubes– mobilemobile– dimerizationdimerization
[1] R. Telling [1] R. Telling et alet al., Nat. Mat. 2, 333 ., Nat. Mat. 2, 333 (2003).(2003).
Simulation: MD with Simulation: MD with Brenner C-C interaction Brenner C-C interaction with long range van der with long range van der Waals extension by Waals extension by
Stuart Stuart et al.et al.
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Caused by vacanciesCaused by vacancies
Young’s modulus:Young’s modulus:
YY00 intact tube Young’s modulus intact tube Young’s modulus
nnii defect concentration defect concentration
aaYiYi coefficients coefficients
Fitted aFitted aYiYi values values
Concentration must be Concentration must be high to reduce Yhigh to reduce Y
Irradiation induced structural Irradiation induced structural weakeningweakening
N
iYi ian
Y
Y
1
0 1
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Structural weakening: Tensile Structural weakening: Tensile strengthstrength
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Load transferLoad transfer
Can irradiation defects improve the load Can irradiation defects improve the load transfer?transfer?
Setup: What is the minimum force required Setup: What is the minimum force required to pull out the inner tube?to pull out the inner tube?
ContributionsContributions– capillary forcecapillary force– tube-tube shear equal at L~200nmtube-tube shear equal at L~200nm– defectsdefects
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Force: defect-free nanotubesForce: defect-free nanotubes
Short (36Å) commensurate / incommensurate tube being pulled out from a longer one (62Å), at T=0KAt room temperature ~0.1MPa
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Tubes with defectsTubes with defects
Single vacancies reconstruct to protrude a Single vacancies reconstruct to protrude a dangling bond 0.5-0.7Å out of plane [1]dangling bond 0.5-0.7Å out of plane [1]
Two vacancies in adjanced planes of graphite Two vacancies in adjanced planes of graphite can form a covalent bond [2]can form a covalent bond [2]
Interstitials are mobile in room temperatureInterstitials are mobile in room temperature– Model: metastable covalent configurationsModel: metastable covalent configurations
[1] El-Barbary [1] El-Barbary et alet al., PRB 68, 144107 (2003).., PRB 68, 144107 (2003).
[2] R. Telling [2] R. Telling et al.,et al., Nature Materials 2, 333 (2003). Nature Materials 2, 333 (2003).
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Two vacancies
Interlayerinterstitial
Interlayer dimer
One vacancy(not covalent)
Tubes with defectsTubes with defects
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Inter-shell bond strength: resultsInter-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 2ndCosires 2004 Helsinki June 28th – July 2nd
Nanotube bundle stiffeningNanotube bundle stiffening
Ref. [1]: electron irradiation of bundles of Ref. [1]: electron irradiation of bundles of single-walled carbon nanotubes (SWNTs) single-walled carbon nanotubes (SWNTs) result in result in – (1) dramatic increase of the bundle bending (1) dramatic increase of the bundle bending
modulus modulus – (2) followed by a decrease at higher doses(2) followed by a decrease at higher doses
What is the reason for this nonlinear What is the reason for this nonlinear behavior?behavior?
[1] Kís [1] Kís et alet al., Nature Materials 3, 153 (2004).., Nature Materials 3, 153 (2004).
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Bending modulusBending modulus
Bundle = cylindrical Bundle = cylindrical macroscopic barmacroscopic bar– Bending modulusBending modulus
Simulations: Y,GSimulations: Y,G– Y~vacanciesY~vacancies– G~covalent inter-tube G~covalent inter-tube
bondsbonds– YYBB
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Young’s and shear modulus:Young’s and shear modulus:(5,5)-bundle(5,5)-bundle
aaYY = 1.2Å = 1.2Å
YY00 = 370GPa (uniformly = 370GPa (uniformly
loaded bulk bundle)loaded bulk bundle)
G = aG = aGG n nbondsbonds
aaGG = 14.5 N/m = 14.5 N/m
Ydef anY
Y10
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
Bending modulusBending modulus
Analytical approximations[1]Analytical approximations[1]– Cross sectionCross section– Number of secondary cascade Number of secondary cascade
atomsatoms
NNvacvac(dose, E)(dose, E)
NNbondsbonds(N(Nvacvac,interaction area),interaction area)
Y,G as a function of dose Y,G as a function of dose and Eand E
YYBB
[1] F. Banhart, Rep. Prog. Phys. 62, [1] F. Banhart, Rep. Prog. Phys. 62, 1181 (1999).1181 (1999).
Cosires 2004 Helsinki June 28th – July 2ndCosires 2004 Helsinki June 28th – July 2nd
SummarySummaryY only moderately sensive (-3% for 1/50Å density (5,5))Y only moderately sensive (-3% for 1/50Å density (5,5))Tensile strength may decrease by 50%Tensile strength may decrease by 50%– reconstruction improves strengthreconstruction improves strength
Irradiation induced defects pin CNTs effectivelyIrradiation 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 bonds2) 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).
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