Graphene is one of the most promising materials in the past 5 years for its exceptional

mechanical, electrical, and thermal properties. Graphene is derived from natural graphite

by means of chemical reactions, exfoliation, and thermal reduction. Graphene as a single

monolayer of carbon atoms can be incorporated into various polymers to create a poly-

mer nanocomposite that enhances the base properties of the polymer. To create gra-

phene, an improved exfoliation method is conducted to synthesize graphite to create gra-

phene oxide then reduce it to create graphene. Analysis techniques, such as TEM imaging

observations, are then used to characterize the structure of graphene oxide and graphene

at the nanoscale, measuring the thickness, area, and amount of folding of the layers.

Then, the folding and size are interpreted are used to make hypotheses regarding the rela-

tive advantages adding graphene as a filler to polymers, such as polyurethane, would have

to increase the thermal conductivity over the base polymer for use in small scale thermal

management. Overall, through a simple synthesis graphene can be produced from graph-

ite with optimal characteristics for many nanoscale applications

Graphene Nanosheets can successfully and more easily be synthesized from natural graphite by using a

modified Hummers’ method to create graphene oxide and then thermally reduce graphene oxide to create

graphene nanosheets. The graphene nanosheets observed are all of similar size and according to TEM im-

ages appear to be thin layer crystalline flakes with some folding occurring. These graphene nanosheets are

then soluble in DMF (Dimethylformamide) which make them highly usable as a filler for polymer nanocom-

posites also soluble in DMF. Based on the crystalline structure, thin layers, and exceptional properties of

graphene, this method of producing graphene for polymer nanocomposites can greatly enhance the ther-

Transmission Electron Microscopy were performed on Graphene Oxide samples at high resolution at 100

kV. GO samples were dispersed in 200 proof ethanol to form a dispersion then drops were placed on cop-

per grid for observation. As the image shows, very thin flakes of GO were produced, although with some ir-

regularities caused by either the ethanol dispersion or not fully synthesized particles, possibly traces of wa-

ter, carboxyls, or other particles. The flake is irregularly shaped and roughly 600nm by 500nm with some

uneven edges and folding. One good feature to note is the light color of the flake. As the TEM measures by

density with darker shades having more density, which can be related to thickness, it can be reasoned that

these flakes are very thin in nature, which can be very useful for creating thin nanoscale layers.

Transmission Electron Microscopy were performed on Graphene samples at high resolution at 100 kV. GO

samples were dispersed in 200 proof ethanol to form a dispersion then drops were placed on copper grid

for observation. Several flakes of graphene were observed and as figure 2 illustrates they are of similar size,

with the one flake being .899 nanometers by .438 nanometers. The nanosheets shown have some darker

strips that indicate some folding of the layers of graphene to be slightly thicker. The thinner areas of the

graphene can be concluded to be fairly thin and presumably monolayer graphene. The other areas that ap-

pear to be folded or scrolled, indicated by the darker mainly thin strips, are inherent to graphene. This is

due to thermodynamic stability of graphene and microscopic crumpling which is how these fold are de-

rived

To calibrate the apparatus for measuring thermal impedance, several one inch diameter discs of PPA,

Polyphthalamide, were made to test the device at varying thicknesses. The disc was placed on the copper

bars and made to fit symmetrically with the equal one inch diameter bars. Small amounts of thermal

grease were applied to the discs to reduce the error caused by the thermal resistance of the different solid

materials and any air that may have been present between the solid surfaces not reduced by the added

pressure. The device was then used as shown in the diagram of the cut bar apparatus above and current

was lead to the upper bar creating a heat source which then traveled along the copper bar, through the

specimen, and through the bottom copper bar and lastly absorbed by the cooling unit. These trials were

run for 30 minutes each time, 5 times, and because the pressure was controlled by the tightness of a screw

done by human hand, varied but was attempted to be of similar values. The known value of PPA’s thermal

conductivity is estimated to be 20 W/mK by ASTM E1461 standard and our average and graphical values of

12.616 and 17.207 with percent errors of 36.9% and 13.9% are adequate for calibration as some heat is

lost to the atmosphere, insulation, thermal resistance, and air in between the discs.

Sample Th C Tc C P (psi) Q (W) R (C/W) I (C m^2/ W) t (m)

K Calculated

(W/mK)

PPA 1 Disc

28.5569 23.5661 1507.1 2.9946 1.666 0.0009495 0.0127 13.322

29.9543 24.0729 1489.5 2.4687 2.3824 0.001363 0.0127 9.3195

30.403 24.2351 1481.5 2.545 2.4235 0.001386 0.0127 9.1615

28.4905 24.0851 1080.4 2.98254 1.4771 0.000845 0.0127 15.0313

29.1574 24.2491 1083.8 3.0227 1.6238 0.000929 0.0127 13.6734

PPA 2 Discs

32.8075 23.9406 1853.7 2.3282 3.7659 0.002154 0.0254 11.6597

33.146 24.0606 1829.5 2.41254 3.76591 0.002154 0.0254 11.7915

33.29 24.1166 1808.4 2.43663 3.76479 0.002153 0.0254 11.795

33.3785 24.1666 1789.3 2.3844 3.8634 0.00221 0.0254 11.4939

31.204 23.5291 1909 2.1195 3.6211 0.002071 0.0254 12.263

PPA 3 Discs

33.5645 23.5816 1862.5 2.12753 4.51153 0.002581 0.0381 14.764

35.049 23.7881 1851 2.16761 5.19493 0.002971 0.0381 12.8218

32.8855 23.4846 1812.1 1.97496 4.76005 0.002723 0.0381 13.9932

34.281 23.7021 1835.9 2.25598 4.68927 0.002628 0.0381 14.2044

34.154 23.7456 1811.5 2.17972 4.77511 0.002731 0.0381 13.9491

Abstract

Background

Characterization of Graphene Oxide

Characterization of Graphene

Calibration of Cut Bar Apparatus

Conclusion

Calibration of Cut Bar Apparatus

The Cut Bar Apparatus is a device used to measure the thermal

conductivity and thermal impedance of Type I, II, and III material

following the standard ASTM D5470. The device uses the heat

conduction between two parallel surfaces of the same material

and properties, one inch diameter copper bars for this device,

having a test specimen of known thickness in between. The ther-

mal impedance can then be calculated by measuring the temper-

ature difference between the two copper bars and heat flow per-

pendicular to the test surfaces with no lateral heat spreading.

Works Cited

Acknowledgments

[1]Mounir El Achaby, Fatima-Ezzahra Arrakhiz, Sebastien Vaudreuil, Abou el Kacem Qaiss, Mostapha Bousmina, Omar Fassi-Fehri, “Mehcanical, Thermal, and

Rheological Preoperties of Graphene-Based Polypropylene Nanocomposites Prepared by Melt Mixing”, Wiley Online Library, 2012

[2]Virendra Singh, Daeha Joung, Lei Zhai, Soumen Das, Saiful I. Khondaker, Sudipta Seal, “Graphene based materials: Past, Present, and Future”, Progress in

Materials Science, 2011, vol 56 8 1178-1271

[3]Haixin Chang and Hongkai Wu, “Graphene-based nanocomposites: prepearation, functionalization, and energy and environmental applications, Energy

Environ Sci, 2013 6 3483

[4]Mingchao Wang, Cheng Yan, and Lin Ma, “Graphene Nanocomposites”, Intech, Chapter 2, 2012

[5]Khan M. F. , Shahil and Alexander A. Balandin, “Graphene-Multilayer Graphene Nanocomposite as High Efficient Thermal Interface Materials”, Nano-

Letters , 2012 12 861-867

Graphene is a monolayer of carbon atoms bonded in hybridization sp2 and is one of the

thinnest materials known to date [1]. Earning the Nobel Prize in Physics for its uses in

2010, this honeycomb lattice material has attracted much attention in the various fields

for its unique and exceptional properties.[2] Due to its structure and composition, gra-

phene has very advantageous electrical capabilities, is one of the strongest and stiffest ma-

terials, and is one of the most thermally conductive materials discovered [3,4]. Because of

this, graphene has attracted much attention is many engineering applications ranging from

sensors, solar cells, energy devices, and nanocomposites. One recently growing area of re-

search is graphene nanocomposites, as pure graphene sheets are limited and supple-

menting various polymers can graphene can have very specialized functions[3]. One prop-

erty, thermal conductivity, is receiving much attention from graphene nanocomposites as

graphene at very low filler levels, ~2%, have shown to improve the thermal conductivity of

the base material [5]. As electronics have become smaller as technology progresses,

reaching that of the nanoscale, the power densities of these electronics have also in-

creased, leading to a need efficient heat dissipation [5]. Because graphene has been rela-

tively difficult to produce in large quantities over the past 5 years, a great deal of research

is being done to find various ways to synthesize graphene from graphite. The chemical

conversion of graphite to graphene oxide and then reduction to graphene appears to be a

likely route to produce graphene in single sheets in moderately sized quantities [2]. Gra-

phene is a material with incredible potential in a vast array of fields and purposes and it

has recognized that several challenges need to be met to fulfill this potential.

Kolby Koeck and Dr. Calvin Li, NovaNano Lab

Department of Mechanical Engineering, College of Engineering, Villanova University, PA

It must be functionalized into sheets

Created as a uniform dispersion

Blend completely with the polymer of choice for the

creation of a composite

Folding and altering of the graphene sheets must be

controlled or diminished [2]

Sponsored by Villanova Center for the Advancement of Sustainability in Engineering and The College of

Engineering at Villanova University

Mentor: Dr. Calvin Li

Assistance: Dr. Eydiejo Kurchan, Dr. Cian Watts