International Journal of Advanced Research in Engineering and Technology (IJARET) Analysis of Polymer and CNT Composites

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
IJARET
Volume 4, Issue 1, January- February (2013), pp. 28-34
© IAEME: www.iaeme.com/ijaret.asp ©IAEME
Journal Impact Factor (2012): 2.7078 (Calculated by GISI)
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ANALYSIS OF POLYMER POLYMETHYL-METHA-ACRALYTE AND
SINGLE-WALL CNT COMPOSITES FOR NEXT GENERATION
ISSUES
A.Saravananpandi Solairajana, Dr.G.Kalivarathanb
a
Research Scholar, CMJ University, Meghalaya, Shillong.
b
Principal/ PSN Institute of Technology and Science, Tirunelveli, Tamilnadu, Supervisor,
CMJ university, Shillong. Email:sakthi_eswar@yahoo.com

ABSTRACT

Carbon nanotubes (CNTs) are normally having outstanding electrical, mechanical,
optical, and thermal properties with significant importance in a wide range of applications
such as quantum wires, tips for scanning probe microscope, and molecular diodes. A polymer
plays an important role in various fields due to their advantages in lightness, ease of
processing, resistance to corrosion, and low cost production. To improve the performance of
polymers, composites of polymers and filler, namely micron-scale aggregate or fibers, have
been extensively used and studied. The use of nano-scale fillers such as metals,
semiconductors, organic and inorganic particles, and fibers, especially carbon structures, are
of particular interest and the subject of intense investigation. The unique properties of carbon
nanotubes offer crucial advantages over other nano fillers. The potential of using carbon
nanotubes as filler in polymer composite has not been fully realized because of processing
difficulties. Currently, there are only a few carbon nanotube-based, commercial products on
the market with improved electrical conductivity. Thermal management such as heat removal
from ICs is a critical problem that limits potential miniaturization, speed and reliability of
micro electronics. For most modern microelectronic devices, cooling is restricted by the
thermal conductivity of the polymeric packaging materials, since polymers typically have low
thermal conductivity as compared to other materials. To enhance the thermal conductivity of
polymers, fillers with higher thermal conductivity is required. The thermal conductivities of
composites (polymer+fillers) is controlled by (i) filler concentration, (ii) filler conductivity,
(iii) filler geometry, (iv) interface conductance between filler and polymer, and (v)
homogeneity of the filler dispersion. The small particle sizes of nano fillers are expected to
disperse more homogeneously within a polymer host than larger micro/milli-fillers. However,
there remain serious gaps in the fundamental understanding of the interaction between nano-
fillers and polymers that lead to the properties of the composite materials.

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1.0 INTRODUCTION

Relaxation processes in amorphous materials are particularly important to
understanding macroscopic properties. Calorimetry has revealed enthalpic relaxations
occurring near the glass transition Tg in polymers aged after a variety of heating treatments.
It is well known that annealing or variation of heating and cooling rates leads to significant
hysteresis in Tg because of structural relaxations. The introduction of nano-fillers is expected
to strongly influence these short-range structural relaxations. However, the effective
utilization of CNTs in polymer composite applications strongly depends upon the
quality/uniformity of the nanotubes and the ability to disperse them homogeneously
throughout the polymer host. Thus, the main objective of this work is to produce and
investigate polymer+Single-wall CNT (SWCNT) nano composites materials, which are
candidates for next-generation of high-strength, light weight, and enhanced thermal
conducting materials. This report describes a simple yet effective method to controllably
disperse SWCNTs in the polymer polymethyl-metha-acralyte (PMMA) and presents a
detailed calorimetric study using modulation (ACC) and modulation-differential-scanning
(MDSC) calorimetric techniques. The PMMA+SWCNT composites were prepared by
dispersing SWCNTs and PMMA in a chloroform solution using sonication then slowly
evaporating the chloroform leaving a homogeneous dispersion. The specific heat and
effective thermal conductivity of the composites were determined by ACC from 300 to 400 K
as a function of SWCNT content. An enhancement of the effective thermal conductivity is
observed as the mass fraction of SWCNTs (φm) increases from 0.014 to 0.083. These
experimental results are in good agreement with a simple geometric model at low SWCNT
content but are better described by more sophisticated models above φm = 0.034. The glass
transition dynamics of pure PMMA and PMMA+SWCNT samples were studied by MDSC as
a function of temperature scan rate. The hysteresis between heating and cooling of the
reversible specific heat decreases with decreasing scan rate for pure PMMA but is essentially
unchanged in the composites, indicating the SWCNT may be quenching glassy structural
dynamics. In all samples, the effective glass transition temperature, Tg increases with
increasing scan rate (though less so for higher φm SWCNTs) but the MDSC determined Tg
are consistently below the scattered values determined by the ACC method. This discrepancy
is attributed to the effect of prolonged heat treatment of the composite for the ACC
measurements. Following this introduction, the experimental procedures for the calorimetric
methods and sample preparation and this again follow results and discussion with theoretical
models for thermal conductivity in composite systems. A general conclusion in the end
describes future directions.

2.0 MODULATION CALORIMETRY

In the ACC technique, the sample and cell, loosely coupled to a constant thermal bath,
are subjected to a small oscillatory heat input. The specific heat and the effective thermal
conductivity can be determined by measuring the frequency dependence of the amplitude and
phase of the resulting temperature oscillation. The heat input, P0e−!t with P0 ≈ 0.5 mW, is
supplied to the sample+cell and typically results in a modulated temperature having an
amplitude Tac ≈ 5 mK. In the sample+cell “sandwich” or “stack” arrangement used in this
study, the total measured heat capacity is written as C = Cs+Cc, where Cs is the heat capacity
of the PMMA or PMMA+SWCNT composite sample and Cc is the heat capacity of cell. The
cell heat capacity consists of Cc = CH + CAg + CGE, where CH is the heater, CAg is the

29


silver sheets, and CGE is the GE varnish (used to attach all the components) contribution.
The heat capacity of the PMMA or PMMA+SWCNT composite is Cs = C − Cc and specific
heat capacity determined as Cp = Cs/ms, where ms is the mass of the sample. The
contribution of the carbon-flake thermister, used to measure the temperature, is small
compared to all other components and is neglected.
The ACC experimental procedure details can be found elsewhere and the method to estimate
the effective thermal conductivity can be found. The effective thermal conductance Ks in
units ofWK−1, the inverse of the thermal resistance, of the sample is given by

where τe = ReCs is the external thermal relaxation time constant, Re the external thermal
resistance, ω the oscillatory frequency, and φ =θ+ π/2 is determined from the phase shift
between the heat input and resulting temperature change. With the geometric dimensions of
sample+cell configuration, the effective thermal conductivity κs in units of W m−1 K−1 can be
calculated directly as κs = KsL/A, where L is the thickness and A is the cross-sectional area
of the sample. High-resolution ACC was performed using a home-built calorimeter. The
general sample+cell configuration consisted of a “sandwich” or “stack” arrangement of
heater, thin silver sheet (0.1 mm thick, 5 mm square), PMMA/SWCNT/PMMA+SWCNT
sample, thin silver sheet, and thermistor, all held together by thin applications of GE varnish.
Here, the two silver sheets do not directly contact each other. The sample area closely
matches the dimensions of the heater attached to one silver sheet. A 120 strain-gauge heater
is attached to one side of the “stack” and a 1 M carbon-flake thermistor to the other side by
GE varnish. The sample was kept inside a thermal bath maintained at a controlled fixed
temperature. By supplying an oscillating voltage to the heater, small temperature oscillations
are induced in the sample+cell detected by the thermister. Scanning temperature is
accomplished by changing the bath temperature. The resolution of the sample+cell and bath
temperatures are in µK range. Modulated (temperature) differential scanning calorimetry
(MTDSC/MDSC) allows for simultaneous measurements of the heat flow and heat capacity.
This is a more refined version of the conventional DSC method. MDSC differs from
conventional DSC in that the sample is subjected to a more complex heating program,
incorporating a sinusoidal temperature modulation onto an underlying linear heating ramp.
Whereas DSC is only capable of measuring the total heat flow, MDSC can simultaneously
determine the nonreversible (kinetic component) and the reversible (heat capacity
component) heat flows. In this MDSC technique, the reversible heat capacity signal was
determined automatically by integrating the total heat flow rates over time. A detailed
description of the MDSC method can be found elsewhere. The MDSC experiment was
performed using a Model Q200 MDSC from TA Instruments, Inc. Samples were heated for
15 min at 127 0C in vacuum to remove any trapped chloroform, prior to mounting in the
MDSC, and subjected to underlying heating and cooling rates of 10, 5, 1, 0.5, and 0.1 K/min
and a temperature modulation amplitude of 0.6 K with a period of 60 s. Dry ultra pure
Nitrogen gas was purged through the sample holder in a rate of 50 ml/min during the
experiment.

30


3.0 PREPARATION OF PMMA+SWCNT COMPOSITES

The polymer PMMA (Mn = 120, 000 g mol−1, obtained from Aldrich) was first
dissolved in a dilute chloroform solution. The required amount of SWCNTs (Helix Materials
Solutions, TX, purity > 90 %, ash ≈ 5 %) was also dispersed into a dilute chloroform solution
and sonicated for 12 hr to separate the bundles of nanotubes into individual particles.
Scanning electron micrographs of the SWCNT material used in this work, presented in a
previous report, found the diameter to be 1.3 nm and the length varying from 0.5 to 50 µm.
Both the PMMA+chloroform dilute solution and the SWCNT dispersed in chloroform
solution were then mixed together and again kept ≈ 6 hr in an ultrasonic bath. After the
PMMA+SWCNT+chloroform dilute solution was finally mixed with a touch mixer (Fisher
Touch-Mixer model 12-810) for 10 mins, no detectable precipitation was observed.
Immediately after this final mixing, the solution was drop cast onto a thin silver sheet to form
a thin film of PMMA+SWCNT and placed for 6 hrs under
vacuum to remove the chloroform. The typical thickness of the sample film is between 150 to
200 µm. The sample was then sandwiched between two thin silver sheets with GE varnish
and again dried under vacuum to remove any solvents from the varnish.

Figure 1: A: Mixture of PMMA and SWCNTs composites before dispersion, B:
just after dispersion, C: after one day of dispersion, D: after two days dispersion and
E: after 5 days of dispersion. F: is the optical micrograph images shows poor quality
of dispersion, which was taken without sufficient time of sonication and mixing with
touch mixture, G: shows the good quality of dispersion of SWCNTs inside PMMA with
sufficient time of dispersion and then with touch mixture.

All samples have essentially the same thickness and cross-sectional areas. Thus, the thermal
contact resistance of all samples are approximately same and should not play a role in
comparing results as a function of SWCNT content. For the MDSC measurements, the
samples were sealed inside a standard hermite pan. The mass of the sample pan and reference
pan was very close to each other to minimize the uncertainty of measurement.

31


4.0 RESULTS AND DISCUSSION

The specific heat of all samples exhibits similar temperature dependence from ≈ 300
to 400 K with only a small change in its absolute value. Since φm is small, Cp is not expected
to vary substantially and so these results more reflect the reproducibility of the absolute value
of Cp measurements by the ACC technique. The experimental Cp value for pure PMMA is
found to be 1.61 J g−1 K−1, about 10 % above the literature value and within 18 % at 307 K
of the value Specific heat values of pure PMMA and PMMA+SWCNT composites at 300 K
(glass state) and 399 K (liquid state). The Cp values of PMMA+SWCNT composites vary
slightly from pure PMMA at room temperature and in a manner similar to that reported for
composites of nanotubes dispersed in polystyrene. The variation of Cp values between
PMMA and PMMA+SWCNT composites is likely due to experimental uncertainty,
especially in the mass measurements of the sample+cell components.

Figure 2: The effective specific heat (top panel) and thermal conductivity (bottom
panel) of pure PMMA and five PMMA+SWCNTs composite samples from 300 to 400 K.
See legend. In lower panel, the definition of the effective thermal conductivity increase
between the glass and liquid state δκ is presented.

the effective thermal conductivity κ using ACC of pure PMMA and PMMA+SWCNT
samples from φm = 0.014 to 0.083. The effective thermal conductivity was derived from the
heat capacity measurements and frequency scans performed at regular temperature intervals,
the details of the experimental derivation of κ can be found elsewhere. The effective κ for
pure PMMA was found to be 0.172 W m−1 K−1 at 300 K and increases with temperature
revealing a step-like feature near and about the glass transition. The absolute value of the
derived κ is within 14 % at 307 K and 9 % at 352 K of the literature value for pure PMMA
The effect of a homogeneous random dispersion can be crucial because once the nanotube
concentration increases, the nanotubes tendency to bundle increases. Once bundles form, the
thermal pathways through a network of SWCNT become ’jammed’ resulting in a more
modest increase in κ. The influence of the nanotube geometry, average length and diameter,

32


on the thermal conductivity of the composite can also be large since these factors directly
influence the packing fraction of SWCNT that in turn plays an important role in the
enhancement of the thermal conductivity. Also, the diameter of the nanotube is important
because, in general, the contact resistance decreases with increasing CNT diameter due to the
larger contact area in addition to the increase in the number of contacts per unit volume. The
thermal boundary resistance between carbon nanotubes and polymer/liquid environment
composites has been simulated and indicate large local temperature gradients as a function of
distances from the nanotube long axis with constant radial heat flow. It was estimated that the
temperature decreases 40 % just 20 0A away from the long axis of the nanotubes, in the
polymer-liquid interface region. This particular simulation result suggests that large
Enhancement of κ in these composites would only be expected for samples with small mean
distance between CNTs, hence high φm.

Figure 3: Log-log plot of the percent enhancement of the thermal conductivity,κ from pure
PMMA (top panel) and the change in thermal conductivity δκ (bottom panel) of
PMMA+SWCNT composites between the glass (300 K) and liquid states (399 K), as a
function of SWCNT mass fraction φm. Arrow indicates the δκ for pure PMMA

5.0 CONCLUSION

This work presents a detailed calorimetric study of the specific heat and effective
thermal conductivity of a macroscopic arrangement of randomly dispersed SWCNTs inside a
polymer host. Using ACC and MDSC techniques, the enhancement of the effective thermal
conductivity is significant with increased loading of SWCNTs. Higher thermal conductivity
of polymer+CNT composites can be achieved by using suitable dispersion methods and
higher quality nanofiller materials. The glass transition characteristics, thermal conductivity,
electrical conductivity, and mechanical properties of polymer composites can be controlled
by adjusting the properties of the nanofillers. The increase in κ with increasing φm of
SWCNT is consistent with essentially independent particles for low concentration that is

33


describable by a simple Geometric model. For SWCNT higher than φm ൌ0.034, a model that
takes into account the packing fraction as well as nanoparticle shape is needed and indicates
the onset of interactions among SWCNT, suggesting the presence of a spanning network. The
increase in the zero-scan rate glass transition temperature and suppression of the enthalpic
hysteresis supports the view that the random inclusions of SWCNT in PMMA quenches
structural relaxations and stabilizes the glass state. Continued experimental study, specifically
by rheological techniques, is required for these types of complex composite systems as well
as a more comprehensive modeling to properly understand and calibrate/engineer the
macroscopic properties.

REFERENCES

[1] S. J. Tans, M. H. Devoret, H. Dai, A. Theses and R. E. Smalley, Nature., 386, 474 (1997).
[2] H. Dai, J. H. Hafner, A. G. Rinzler, D. T. Colbert, and R. E. Smalley, Nature., 384, 147
(1996).
[3] S. J. Sander, J. Tans, A. R. M. Verschueren, and C. Dekker, Nature., 393, 49 (1999).
[4] Ijima Sumio, Helical microtubules of graphitic carbon,Nature., 354, 8, No.56 (1991).
[5] S. Glushanin, V. Y. Topolov, and A. V. Krivoruchko, Materials Chemistry and Physics.,
97, 357 (2006).
[6] P. Hine, V. Broome, and I. Ward, Polymer., 46, 10935 (2005).
[7] N. Cioffi, L. Torsi, N. Ditaranto, G. Tantillo, L. Ghibelli, L. Sabbatini, T. BleveZacheo,
M. D. Alessio, P. G. Zambonin, and E. Traversa, Chemistry of Materials.,317, 5255 (2005).
[8] A. Pelaiz-Barranco and P. Marin-Franch, J. Appl. Phys., 97, 034104 (2005).
[9] A. Bar-Cohen, A. Watwe, and K. N. Seetharamu, Fundamentals of Thermal Management
in Fundamentals of Microsystems Packaging, Chapter 6, Ed., R.R. Tummala, McGraw Hill,
New York (2001).
[10] B. Wunderlich, Thermal Analysis of Polymeric Materials. Springer-Velag: Berlin,
Heidelberg, (2005).
[11] B. Wunderlich, Thermal analysis. New York: Academic Press., 135, 205 (1990).
[12] M. Meyyappan, Carbon nanotubes science and applications, CRC Press: Boca Raton, FL
(2005).
[13] P. J. F. Harris, Carbon nanotubes and related structures new materials for the twenty-first
century;Cambridge University Press: Cambridge (2001).
[14] www.pageout.net/user/www/l/y/lyee/specificheat.pdf.
[15] M. J. Assael, S. Botsios, K. Gialou and N. Metaxa,International Journal of Ther-
mophysics,26, ,1995 (2005).
[16] C. Rauwendal,Polymer Extrusion,PUBLISHER - HanserMunich, GDR (1986).
[17] S. Agarwal, M. Mashud, K. Khan, and R. K. Gupta, Polymer Eng and Science., 129, 1
(2008).
[18] Y. Yang, M. C. Gupta, J. N. Zalameda and W. P. Winfree, Micro and Nano Letters, 3,
No.2, 35-40 (2008).
[19] L. E. Nielsen, Ind. Eng. Chem. Fundam., 13, 17 (1974).
[20] R. L. Hamilton and O. K. Crosser, Ind. Eng. Chem. Fundamen., 1, 187 (1962).

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