International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Electrical conductivity of untreated multiwalled
carbon nanotube/epoxy composites
A.Badran ALsafee 1, Ikram A. Al-Ajaj2and A. shawky Khalil 3
Baghdad University, College of Science, Department of Physics
Abstract
Untreated multi-walled carbon nanotubes (MWCNTs) with different weight percentage (0.1,0.5,1,2 ,3, 4 and 4.5) % wt. were used
to fabricate MWNT/epoxy composite samples by hand lay up method. Ultrasonic mixing process was used to disperse the
nanotubes into the resin system. The electrical conductivity of multiwalled carbon nanotubes (MWNT)/epoxy composites is
investigated from 2x10-5 for pure epoxy to 1x10-2 for the concentration 4.5% wt. of MWCNTs.
Keywords: Epoxy, Electrical conductivity, Nanocomposites, MWCNTs
1. Introduction
Since the carbon nanotubes (CNTs) were discovered by Iijima [1] in 1991, they have attracted considerable attentions due
to their unique structural, electrical, and mechanical properties [2] , [3],[4].
Carbon nanotubes (CNTs), one graphene layer (SWNT) or many graphene layers wrapped onto themselves (MWNT) are
a novel crystalline carbon form. The recent theoretical and experimental investigations indicate that they have properties
suitable for applications in many fields. Their interesting high electrical conductivity have been the subject of many
research works [5] , [6] , [7].
In order to achieve optimal enhancement in the properties of CNT/polymer composites, two key issues should be
considered: homogeneous dispersion of CNTs in the polymer resin and strong interfacial bonding between the CNTs and
the polymer matrix [8]. Several researchers have prepared epoxy resin/CNT composites to obtain outstanding electrical
properties. A. Allaoui et al [9] fabricated epoxy resin/CNT composites , they mixed 0.5 , 1 and 4 % wt. of MWCNTs with
epoxy resin their results indicate an improvement for electrical conductivity . Jianfei Chang et al . [10] were developed
multiwalled carbon nanotube (MWCNT)/epoxy (EP) composites using microwave curing (m-MWCNT/EP). They have a
very high dielectric constant and low dielectric loss.
In this study, our goal is focused on how to increase the content and the homogeneous dispersion of MWCNTs without a
solvent in the matrix.
2. Materials and experimental methods
2.1 Materials
The multiwalled carbon nanotubes (MWCNTs), used in this study synthesized by thermal chemical vapor deposition
(CVD) procees, were supplied by Intelligent Materials Pvt. Ltd. , these have a diameter of 20–30 nm and a length of 10–
30 micrometers as shown in figure (1) which represented a Scanning Electron Microscope(SEM) and (2) which
represented Transmission Electron Microscope(TEM) . Epoxy as a matrix (Nitofill, EPLV with Nitofill EPLV hardener
from Fosroc Company). The mixing ratio for resin and hardener is 3:1 and gelling time 40 minute at 35 oC, mixed
viscosity 1.0 Poise at 35 oC , the structure of epoxy is shown in figure (3).
Fig. (1) SEM image for MWCNTs
A Transmission Electron Microscope were measured in TEM Philips CM30 for MWCNTs to indicate their diameter (2030) nm .
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Fig.(2) TEM for MWCNTs.
The chemical structure of epoxy resin is :
Fig.3. Epoxy structure [11]
2.2. Preparation of EP/MWCNTs Composites
The shape samples prepared for dielectrical test suitable to the designation of ASTM (D150) as in figure (4).
Fig. (4). Epoxy and epoxy/MWCNTs composites specimen shape for dielectrical test where; (R) is the diameter of the
sample, (d ) is specimen thickness.
The preparation steps of the neat epoxy and epoxy /MWCNTs composites for dielectrical tests were prepared by hand lay
up technique by mixing process which consists of three steps.
2-2.1 Neat epoxy preparation
Firstly epoxy resin and hardener are weighted for suitable mixing ratio, and then manually mixing then epoxy resin and
hardener by magnetic stirror at 600 rpm for 30 minutes to have good homogeneity between epoxy resin and hardener.
Secondly, for better homogeneity homogenizer device were used for 4 minutes. The third step as shown in figure (5)
vacuum system was using to remove the bubble before molding the epoxy in the mold as shown in figure (6).
Fig. (5) Vacume system
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Volume 3, Issue 3, March 2014
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Figure (6) Mold of the samples for dielectric test.
2-2.2 Epoxy nanocomposites preparation
The epoxy nanocomposites were prepared with MWCNT with weight percentage 0.1,0.5,1,2,3,4 and 4.5 .Epoxy
/MWCNTs composites were prepared in three steps; firstly, the nanotubes are weighted and manually mixed with epoxy
resin under gloves box in nitrogen atmosphere as shown in figure (7).
Fig. (7) Gloves box (handmade by researcher)
Interaction with water vapor specially increase particles agglomeration and decrease any interaction (chemical or
physical) of particles with polymer chain in the matrix. Nanotubes with epoxy resin were mixed by magnetic stirror at
600 rpm for 30 minutes to have good distribution and less agglomeration. The second step involves that usage of
homogenizer device for 4 minutes to get good dispersion. The hardener was mixed with epoxy resin / MWCNT for 4
minutes by the homogenizer device. Using the homegenizer may cause to increase viscosity and increase epoxy resin
temperature then sample container should be put in a cold water container to avoid high temperature which decrease time
of gelling making the composite hard to mold.The third step was using vacuum system (10-2 bar) to remove the bubble
before molding . The samples which explained in figure (8) were left for 72 hours before pulling out from molds and left
in the vacuum chamber as shown in figure (9) for 10 days before any test to get better curing conditions.
Fig. (8). Epoxy and epoxy /MWCNTs composites specimens for dielectrical test
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
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Volume 3, Issue 3, March 2014
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Fig.(9) Vacuum chamber
2.3. Scanning Electron Microscope (SEM) Images of EP/MWCNTs Nanocomposites Topography of Fractured
Surface
Figure 10 shows the SEM micrographs taken from the fracture surfaces of the epoxy and epoxy/MWCNTcomposites. The
smooth fracture surface of the neat epoxy is a typical feature of brittle fracture behaviour. As the filler content increases
the surface roughness increases, suggesting that the crack propagation in the nanocomposite is opposed by rigid and stiff
fillers. In other words, since the segments of primary crack front had to move quickly between the fillers, more energy is
needed for such local deviations. In fact it leads to higher fracture toughness.As indicate in the figures 10
a,10b,10c,10d,10e,10f,10g,and10 h.
(a) pure epoxy
(c) 0.5%wt.MWCNTs
(e) 2%wt.MWCNTs
Volume 3, Issue 3, March 2014
(b)0.1%wt.MWCNTs
(d)1%wt.MWCNTs
( f ) 3%wt.MWCNTs
Page 25
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Volume 3, Issue 3, March 2014
(g) 4%wt.MWCNTs
ISSN 2319 - 4847
(h) 4.5%wt.MWCNTs
Fig.10. SEM images of EP and EP/MWCNTs composites with different weight percentages (0.1,0.5,1,2,3,4and 4.5)
3. Results and Discussion
3.1 Relative Permittivity (Real Part) of Epoxy and Epoxy / MWCNTs
Figure 11 is shown the variations of permittivity with respect to frequency for epoxy and epoxy / MWCNTs composites
for the concentrations 0.1 , 0.5 , 1 , 2 , 3 , 4 and 4.5 wt. % of MWCNTs. The measurement temperature is kept constant ,
hence , its influence on the permittivity behavior can be neglected . It can be seen from figure 4-5 that the permittivity of
epoxy and and epoxy/MWCNTs composites increase with decreasing frequency .
The measurement temperature is kept constant , hence , its influence on the permittivity behavior can be neglected . It can
be seen from figure 9 that the permittivity of epoxy and and epoxy/MWCNTs composites increase with decreasing
frequency . The epoxy component of permittivity is governed by the number of orientable dipoles present in the system
and their ability to orient under un applied electric field .At lower frequencies of applied voltage , all the free dipolar
functional groups in the epoxy chain can orient themselves resulting in ahigher permittivity value at these frequencies .
As the electric field frequency increases , the bigger dipolar groups find it difficult to orient the same speed as the
alternating field , so the contributions of these dipolar groups to the permittivity goes on reducing resulting in a
continuously decreasing permittivity of the epoxy system at higher frequencies .Similarly , the inherent permittivities in
MWCNTs also decrease with increasing frequencies of the applied field . This combined decreasing effect of the
permittivity for both epoxy and MWCNTs result in a decrease in the permittivity of nanocomposites also when the
frequency of the applied field increase. There are several parameters could be affect the dielectrical properties of epoxy
nanocomposites such as applied field frequency and the concentration of nanotubes.
Fig.11. Real permativity Vs frequency for EP and EP/MWCNTs with different weight percentages (0.1,0.5,1,2,3,4and
4,5)
3.2 Tan Delta of EP/MWCNTs composites
The variations of tan delta with the frequency for epoxy and EP/MWCNTs composites with 0.1,0.5,1, 2, 3, 4and 4.5 %
wt. of MWCNTs at room temperature are shown in figure (12)
Volume 3, Issue 3, March 2014
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
EP/0.1 MWCNTs
0.012
0.01
Tan delta
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
EP/0.5 MWCNTs
0.012
0.01
Tan delta
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
EP/1% MWCNTs
0.014
0.012
0.01
Tan delta
0.008
0.006
0.004
0.002
0
0
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200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
Page 27
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
EP/3%MWCNTs
0.012
Tan delta
0.01
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
EP/4%MWCNTs
0.0065
0.006
Tan delta
0.0055
0.005
0.0045
0.004
0.0035
0.003
0
200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
4.5%MWCNTs
0.012
0.01
Tan delta
0.008
0.006
0.004
0.002
0
0
200,000
400,000
600,000
Frequency (Hz)
800,000
1,000,000
1,200,000
EP/1% MWCNTs
0.014
0.012
0.01
Tan delta
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (Hz)
800000
1000000
1200000
Fig. (12) Tan delta versus frequency for EP and EP/MWCNTs composites with 0.1 , 0.5 , 1, 2, 3, 4 and 4.5 weight
percentage of MWCNT
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
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Figure (12) shows the behavior of tan delta with increasing frequency . Tan delta increases with increasing frequency and
then slowly start to decrease .Tan delta depends on the electrical conductivity in the epoxy composites. The electrical
conductivity depends on the number of charge carriers and frequency of the applied electric field on the composites. The
increases of weight percentage of MWCNTs in EP/MWCNTs composites lead to increasing the sources of charge
carriers. The charge carriers can travel along the filler and move directly from one filler to another. Increasing the
amount of filler leads to overlapping interaction zones of nanotubes inside the epoxy matrix of EP/MWCNTs composites.
The overlapping of interaction zone (percolation effect) depends on; weight percentage , aspect ratio, purity and the
dispersion of MWCNTs . On the other hand , the high immobile epoxy nanolayer formed around nano tubes . Hence,
epoxy chains close to the immobile epoxy nanolayer surface will restrain the charges transport through chains and
interfaces zones. The high immobile epoxy nanolayer depend on the area of interfacial surface and the diameter of
nantubes .
Increasing the weight percentage of MWCNTs enhance electrical conductivity as shown in figure (13), and hence, tan
delta.
Electrical conductivity (1/Ωm)
Electrical conductivity (1/Ωm)
EP
3.50E-05
3.00E-05
2.50E-05
2.00E-05
1.50E-05
1.00E-05
5.00E-06
0.00E+00
0
200000
400000
600000
800000
1000000
Frequency (Hz)
EP/0.1%MWC…
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
800000
1000000
1200000
Electrical Conductivity
(1/Ωm)
Electrical Conductivity (1/Ωm)
Frequency (HZ)
EP/0.5%MWCNTs
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
0
200000
400000
600000
Frequency (HZ)
800000
1000000
1200000
EP/1%MWCNTs
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
0
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200000
400000
600000
Frequency (HZ)
800000
1000000
1200000
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Electrical Conductivity
(1/Ωm)
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
EP/2% MWCNTs
0.01
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (HZ)
800000
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (HZ)
800000
1000000
Electrical Conductivity
(1/Ωm)
1200000
EP/4%MWCNTs
0.01
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
800000
Frequency (HZ)
1000000
1200000
EP/4.5%MWCNTs
0.016
Electrical Conductivity (1/Ωm)
1200000
EP/3%MWCNTs
0.01
Electrical Conductivity
(1/Ωm)
1000000
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0
200000
400000
600000
Frequency (HZ)
800000
1000000
1200000
Fig. (13) Electrical conductivity versus frequency for epoxy and EP/MWCNTs composites with 0.1 , 0.5 ,1, 2, 3, 4and 4.5
weight percentage of MWCNTs
Conclusion
This study has demonstrated the intrinsic potential of the CNT. Small quantity addition can modify considerably the
electrical behavior of an insulator polymer matrix. The exceptional electrical properties of MWNT have been used to
improve the performance of an insulator epoxy matrix nanocomposites. The addition of CNT into the epoxy matrix has a
remarkable effect on the electrical properties. According to our results from the electrical conductivity epoxy considered
an insulators but the addition of MWCNTs transformed the nanocomposites to semiconductors.
References
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
[5] Robertson DH, Brenner DW, Mintmire JW. Energetics of nanoscale graphitic tubules. Phys Rev B
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