Thomas Laude's pages - Science de la matière et de l'énergie

Thomas Laude's pages - Science de la matière et de l'énergie

Thermal conductivity (k) of polymer composites

Abstract:

k of polymers is very low (~ 0.2 W/mK). This can be increased by 2 orders adding h-BN platelets without affecting electric conductivity. For thermal properties carbon and BN are comparable, due to a phonon-dominated thermal conduction. k of nanotubes is close to that of in-plane graphite which is excellent (3000 W/mk). The k of polymer/nanotube composite is now being studied by several groups but results are still unpublished.

At this point, it is probable that NT filling will drastically increase thermal conductivity. However, it is not clear if the benefit will be higher than that of standard powder fillers. We may hope that same level of increase can be obtained at much lower concentration of the filler, and hence with far less deterioration to the original properties of the polymer.

1. Orders of magnitude of thermal properties of various materials

Hukseflux Thermal Sensors - P.O. Box 2816 - 2601 CV Delft - The Netherlands - Copyright © 1999 to 2004 

	Thermal conductivity at 20° C W/mK	Density at 20° C Kg/m3	Volumetric heat capacity at 20° C 106 J/m3	Thermal diffusivity at 20° C 10-8 m2/s
Air	0.025	1.29	0.001	1938
Glycerol	0.29	1260	3.073	9
Water	0.6	1000	4.180	14
Ice	2.1	917	2.017	104
Olive oil	0.17	920	1.650	10
Gasoline	0.15	720	2.100	7
Methanol	0.21	790	2.500	8
Silicone oil	0.1	760	1.370	7
Alcohol	0.17	800	2.430	7
Aluminium	237	2700	2.376	9975
Copper	390	8960	3.494	11161
Stainless Steel	16	7900	3.950	405
Aluminium Oxide	30	3900	3.413	879
Quartz	3	2600	2.130	141
Concrete	1.28	2200	1.940	66
Marble	3	2700	2.376	126
Glass	0.93	2600	2.184	43
Pyrex 7740	1.005	2230	1.681	60
PVC	0.16	1300	1.950	8
PTFE	0.25	2200	2.200	11
Nylon 6	0.25	1140	1.938	13
Corian (ceramic filled)	1.06	1800	2.307	46
Sand (dry)	0.35	1600	1.270	28
Sand (saturated)	2.7	2100	2.640	102
Glass pearls (dry)	0.18	1800	1.140	16
Glass pearls (saturated)	0.76	2100	2.710	28
Wood	0.4	780	0.187	214
Cotton	0.03	--	0.001	--
Leather	0.14	--	0.001	59
Cork	0.07	200	0.047	150
Foam glass	0.045	120	0.092	49
Mineral insulation materials	0.04	100	0.090	44
Plastic insulation materials	0.03	50	0.100	30

2. k measurement of pyrolytic graphite

G

k with temperature for graphite

raphite is remarkable for its very anisotropic k. It is an excellent thermal conductor through parallel planes (2000 W/mK at room T), but a thermal insular through perpendicular planes (0.1 W/mK at room T).

Y. S. Touloukian, R. W. Powell, C. Y. Ho, and P. G. Klemens, Thermophysical properties of matter (IFI/Plenum, New York, Washington, 1970), Vol. 2, Thermal conductivity, p. 41

3. k measurement of pyrolytic h-BN at room T

Measurements are almost absent for pyrolytic h-BN because pyrolytic h-BN is little available. The measurement of an imperfect pyrolytic h-BN sample indicates 60 W/mK for parallel planes, and 2 W/mK for perpendicular planes. The relatively small difference between parallel and perpendicular conductivity is probably due to bad alignment in the sample.

Advanced Ceramic Corporation, Measurements on pyrolitic BN, 22557 West Lunn Road, Cleveland, Ohio USA 44149 (web site only).

A similar k for graphite and h-BN is possible. Indeed, thermal conductivity of graphite and h-BN is dominated by phonon conductivity, which is expected similar for both materials.

4. k of carbon nanotubes (measurements and calculations):

k of carbon nanotubes has been studied by many authors. All agree that it is similar to the parallel k of graphite.

Shi measured k = 3000 W/mK at 300K for a MWNT, and k = 1200 W/mK at 300K for a 150 nm MWNT bundle. Hone et al. estimated k =1750 to 5800 W/mK for a SWNT rope at room T. They also reported a linear increase of k with T at low T, and evaluated the phonon mean free path at 0.5 to 1.5 micron.

L. Shi, Mesoscopic thermophysical measurements of microstructures and carbon nanotubes, PhD Thesis, Univ. of California, Berkeley, 2001

J. Hone, M. Whitney, C. Piskoti, and A. Zettl, thermal conductivity of single-walled carbon nanotubes, Phys Rev B 59, 2, R2512 (1999)

Che calculated for a (10,10) SWNT k = 2980 W/mK. Srivastava et al. calculated for a (10,10) SWNT k = 1500 W/mK at 300K, and a peak k = 2700 W/mK near 400K. Berber calculated a very high value of k = 6600 W/mK for a SWNT. Maruyama calculated k for a tube shorter than phonon mean free path, and found an increase from 200 to 600 W/mK with length.

S. Berber, Y. Kwon, and D. Tomanek, Unusually high thermal conductivity of carbon nanotubes, Phys Rev Lett, 84, 4613-4616 (2000)

M. Osman, and D. Srivastava, temperature dependence of the thermal conductivity of single-wall carbon nanotubes, nanotechnology 12, 21-24 (2001)

A molecular dynamics simulation of heat conduction of a finite length single-walled carbon nanotube, S. Maruyama, Microscale thermophysical engineering 6010 (2003)

5. k of polymer/particle composite materials

Several ceramic platelets-polymer composite have been studied. h-BN was reported to give best results (13 W/mK).

Thermal conductivity of platelet-filled polymer composites, J. of the American ceramic society, April 2002, 85, 4, 851-857

The modelisation of polymer/nanoparticule composite was undertaken.

J. of Appl. Phys., 94, 10, 6785-6788 (2003)

Thermal conductivity of particle reinforced polymer composites, I.H.Tavman

Some thermally conductive polymers are already commercially available, some of which are also electrically resistant.

6. k of polymer/carbon nanotube composite material

k measurements of polymer/carbon nanotube composites is now being studied by several groups, but results are still unpublished. The Science Daily reported that the Rensselaer Polytechnic Institute obtained disappointing results and argued that it was due to the nanotube/matrix interface. One team at The University of Tennessee USA, has measured k for an aligned NT mat immerged in aminoepoxy resin, but results are under publication.

A report of polypropylene/vapour grown carbon fibres indicates up to k = 5.4 W/mK for 23% filler addition.

R. Kuriber, M. Alam, Thermal conductivity of thermoplastic composites with submicrometer carbon fibers, Exp. Heat Transfert 15, 19-30

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