Eng Presentation 1

8/2/2019 Eng Presentation 1

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Structure and energeticsof carbon nanotube ropes


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Introduction

Carbon nanotube is the strongest man made material which has

excellent mechanical properties. It s stronger than Kevlar which has ever

been the best material for producing bullet-proof armor. Carbon nanotube

structure consists of whole carbon atom bonding in a sheet form (in nano

scale) that be rolled up like a tube, so Its called Carbon nanotube

Carbon nanotubeKevlar


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Even It consists of whole carbon atomEven It consists of whole carbon atom

like a charcoal and Graphite (includinglike a charcoal and Graphite (including

diamond). But because of its structure, It isdiamond). But because of its structure, It ismuch stronger than its component-likemuch stronger than its component-like

materials .Some forms are even strongermaterials .Some forms are even stronger

than diamond!!than diamond!!

Diamond s face center

cubic structure


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Hence, the structure and the orientation of molecules play a big

role on material s mechanical properties. Carbon nanotubes are present

mainly in three configurations:

single-walled carbon nanotubes

Multiwalled carbon nanotubes

carbon nanotube bundles


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As the researchers study about the stabilityof carbon nanotubes for using as high strengthmaterial , the carbon nanotubes in a bundle form

are the best for mechanical applications. Theraft-like form of carbon nanotube bundles arewidely produced while there is some weakpoints of this form. Individual carbon nanotubesin the bundles interact with each other through th

e weak van der Waals forces. The van derWaals force which hold nanotubes together areweak in the raft-like structure


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However, The carbon nanotube in a

rope formed from twisted individual tubestogether tend to have higher strength and

provide more stability also.


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Purpose and scope

This Project will focus on the structure and energetics ofcarbon nanotube ropes made from twisted carbon nanotubes by us

ing high-resolution transmission electron microscopy (HRTEM) and

some other simulations of twisted carbon nanotube.

electron microscopic will offers image features of carbonnanotube ropes in a double-strand nanotube rope, a triple-strand n

anotube rope and a larger rope, respectively. The energetic stabilit

y and formation of these carbon nanotube ropes were analyzed thr

ough molecular mechanics calculations.

HRTEM image simulations of a septuple-strand carbon

nanotube rope were also performed in order to compare with the e

xperimental results.


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Design of experiment

The carbon nanotubes in this

experiment were prepared by

electric-arc technique and then

dispersed in methanol. The

carbon nanotubes will be

agitated in ultrasonic bath.

A small drop of the suspension was

then put onto a holey carbon grid and al

lowed to dry in air. Twisted carbon

nanotubes in various cases were

provided for the study.


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HRTEM imaging of the sample was

performed in the transmission electron microscope operated at 200 kV and the images were coll

ected on a Gatan CCD camera.


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Result & DiscussionResult & Discussion

The twisting rate of two carbonThe twisting rate of two carbon

nanotubes are determined bynanotubes are determined by measuring

the axial length and the twisting angles byby

HRTEM image which show the Thetwisted carbon nanotubes rope twist with r

espect to each other along the roping axis

by 90 degree in an axial length of 18 nm,so this two twisted carbon tubes rope are

twisted at a rate of 5 degree/nm.


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Fig. 1 (a) Transmission electron microscopy image of a double-tubule

carbon nanorope. The two tubules twist around their roping axis by about

180 degree


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Fig. 1 (b) Transmission electron microscopy image of a triple-tubule

carbon

nanorope.


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Twisting of individual nanotubes to

form a thicker rope was also observed, alt

hough the twisting features are much mor

e complicated than the small nanotube ropes


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A twisted carbon nanorope composed of

more than 40 individual single-walled carbon

nanotubes.


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The energetic analysis

The structural stability of carbon nanotube ropes was analyzedby carrying out molecular mechanics simulations, which can handle a muc

h larger system of atoms

The energetics stability of nanoropes should be observed

experimentally on only straight carbon nanotube ropes with respect to suc

h parameters as the twisting angle and helicity of individual nanotubes. A

classical force field method was used to account for the interactions between carbon atoms in the carbon nanotube ropes.

To cope with the large model structures for carbon nanotube

ropes that are composed of thousands of atoms, they have only included t

he diagonal, harmonic terms in the force field as follow :

Note that no electrostatic

interactions were considered in

the simulations.


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Twisted energy that was calculatedTwisted energy that was calculatedfrom that equation for simulation of variousfrom that equation for simulation of varioussizes of carbon nanotubes rope aresizes of carbon nanotubes rope arecomparable with result from other morecomparable with result from other moreaccurate method includingaccurate method including the result fromthe result from

the experimentthe experimentTherefore , the simulations of twistedTherefore , the simulations of twisted

energy of carbon nanotubes rope could beenergy of carbon nanotubes rope could beimagined as follow slideimagined as follow slide


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Fig. 3 (a) shows the schematic illustration of a pair of twisting single-walled

carbon nanotubes of the same atomic structure (10, 10) (the indices define

the perimeter vector on graphene [4]) to form a double-strand rope. Each single-walled carbon nanotube was twisted about its axis by an angle and t

hen the twisted nanotubes twine around each other to form a nanotube rop

e of roping angle


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The torsion energy increases harmonically with the distorsion initially

and then increases faster as the nanotube is further twisted.

From the energetic considerations, due to the increase of strainenergy, the distorted structure will not be stable without constraints.

However, if the two twisted carbon nanotubes join together, due to the

tendency of energy minimization,the structure can be stable energetically while

enhancingstructural stability.


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shows the total formation energy as a function of the twist angle b of the

nanotube rope formed by two identical (10,10) nanotubes, each of

which is twisted about its own tubule axis by an angle = 1 = 2 and t

hen the two twisted nanotubes twine around each other by a roping angl

e .


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Fig. 3(c) shows calculated results for the case 1 = 0 and 2 = 5, 10,15, and 20, respectively. As in the first case, the plied carbonnanorope is a meta-stable structure when the roping angle 0 assumes an appropriate value.


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On the other hand, since the structure

of carbon nanotubes is often helical like the DNA molecule, They have also

examined the role of helicity in the formati

on of a plied carbon nanorope.


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Fig. 4. Twisting energy varies with roping angle for combinations of

carbon nanotubes of different helicity(10,10) and (14, 5), (10,10)

and (10,10), (11, 9) and (12, 8) and (10,10) and (13, 7). The length of

all individual carbon nanotubes is about 8.8 nm.


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HRTEM image simulations

The additional simulation of larger carbonThe additional simulation of larger carbon

nanotubes rope was also examine. They foundnanotubes rope was also examine. They found

that thethat the Molecular mechanics simulations of the

septuple-strand carbon nanotube rope show thatthe energy variation relative to the roping angle

is the same as that for the double-strand

nanotube rope.Seven nanotubes of the same

(10,10) were used to form a septuple-strandcarbon nanotube rope, which is shown as a

picture in next slide


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Fig. 5.

(a) Cross-sectional view of a model of a rope-like bundle ofseven carbon nanotubes with diameter of 11 nm. Six carbonnanotubes twist around the central tubule by approximately10, which is comparable to the experimental roping angle of60 in 70nm length. (b) Simulated HRTEM image with electron beam incident in the B direction indicated in (a). White arrows D and E highlight the characteristic image features of pl

ied carbon nanoropes.


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ConclusionConclusion

observing of single-walled carbon nanotubes invarious condition of forming ropes. A double-strand,triple-strand and a larger carbon nanotube rope have been investigated using high-resolution electron microscopy.

Molecular mechanics simulations show that, by twisting asingle model (10, 10) nanotube about its tubule axis, the strain energy increases non-linearly with the twist angle. When two twisted carbon nanotubes join together to form a rope, the nanotube rope is a metastable structure energeti

cally. It has also been demonstrated that the helicity of nanotubes plays an insignificant role in the formation of carbon nanotube ropes.


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