Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Mechanical Properties in Multiwalled Carbon nanotubes/ PAM composites
1 * 1 , Önder Pekcan 2
1 Department of Physics, , 34469, Turkey
2
0, Turkey
Abstract- The mechanical properties of multiwall carbon nanotubes (MWNTs)/polyacrylamide (PAM) composites were studied as a function of
nanotube content. Multiwalled carbon nanotube (MWNT) composites with polyacrylamide (PAM) were prepared via free radical crosslinking
copolymerisation with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. The PAM-MWNT composite gels were
characterized by tensile testing machine. A small content of doped nanotubes dramatically changed Young modulus and toughness, respectively.
Carbon nanotubes (CNTs) have been one of the hottest
research topics since the discovery [1] because of their special
properties and wide potential applications [2].
The mechanical properties of hydrogels with nano materials
are best understood using the theories of rubber elasticity and
viscoelasticity. To derive relationships between the network
characteristics and the mechanical stress- strain behavior,
classical and statistical thermodynamics have been used to
develop an equation of state for rubber elasticity. It is known
the entropic model. From classical thermodynamics, the
equation of state for rubber elasticity may be expressed as [3]
f
U
f
T
L
T,
V T
L,
V
(1)
where f is the refractive force of the elastomer in response to a
tensile force, U is the internal energy, L is the length, V is the
volume, and T is the temperature. For ideal rubber elastic
behavior, the first term in equation 1 is zero. The refractive
force and entropy are related through the following Maxwell
equation
S
f
L
T,
V T
L,
V
(2)
Stress- strain analysis of the energetic and entropic
contributions to the refractive force (Equation 1) indicates that
entropy accounts for more than 90% of the stress. After some
statistical analysis, shear modulus can be defined by
G
(3)
where , the force per unit area and is the extension ratio.
While the thermodynamic and statistical thermodynamic
approaches describe observed rubber-elastic behavior at low
extensions quite well, the equation is invalid higher
elongations [3]
Composite gels were prepared via free radical crosslinking
copolymerization with different amounts of MWNTs varying
in the range between 0.1 and 50 wt%. Compression module of
PAM- MWNTs composite gels at 25°C was determined by
means of a Hounsfield H5K-S model tensile testing machine.
Any loss of water and changing in temperature during the
measurements was not observed because of the compression
period being less than 1 min.
Figure 1(a) and (b) show that young modulus and toughness
depend on the content of MWNTs in PAM, respectively.
Young modulus increases progressively until 3 wt. %
MWNT with increasing nanotube content. At contents above
Young modulus(MPa)
Toughness(kPa)
0,12
0,10
0,08
0,06
0,04
0,02
2
1
0
0,0 10,0 20,0 30,0 40,0 50,0 60,0
0,0 10,0 20,0 30,0 40,0 50,0 60,0
%MWNT
(a)
1.trial
2.trial
(b)
1.trial
2.trial
Figure 1. (a) Young modulus and (b) Toughness dependence
on the MWNTs content in composite gels.
3wt. %MWNTs, the young modulus is decreased marginally
with increasing MWNTs content in Figure 1(a). On the other
hand, at lower content(3 wt.%), the toughness decreases from
the neat composite of 1.3kPa, only exceeding it when the
MWNT content is above 20 wt. % (Figure 1(b)), and then
increases further as the MWNTs content is raised[4].
This work explores the mechanical properties of PAM-
MWNTs composite gels characterized by tensile testing
machine. Our results show that a decrease in length brings
about an increase in entropy because of changes in the end to
end distances of the network chains of PAM-MWNTs
composite gels, thermodynamically. Thus, the entropic model
for composite elasticity is a reasonable approximation.
We thank Argun Talat
measure ments.
*Corresponding author: evingur@itu.edu.tr
Gökçeören for tensile test
[1] S. Lijima, Nature 354, 56, (1991).
[2] P. J. F. Harris, Int. Mat.Rev. 49, 31, (2004).
[3] K. S. Anseth, C. N. Bowman, L. B. Peppas, Biomaterials 17,
1647, (1996).
[4] R. Andrews, D. Jacques, D. Qian, T. Rantell, Acc. Chem. Res.35,
1008, (2002).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 383