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Research Papers: Conduction

Influence of Nanomaterials in Polymer Composites on Thermal Conductivity

[+] Author and Article Information
Wonchang Park, Kyungwho Choi

Department of Mechanical Engineering,  Texas A&M University, College Station, TX 77843

Khalid Lafdi

Carbon Research Laboratory,  University of Dayton, Dayton, OH 45469

Choongho Yu1

Department of Mechanical Engineering,  Texas A&M Universiity, College Station, TX 77843; Materials Science and Engineering Interdisciplinary Program,  Texas A&M University, College Station, TX 77843chyu@tamu.edu

1

Corresponding author.

J. Heat Transfer 134(4), 041302 (Feb 13, 2012) (7 pages) doi:10.1115/1.4005201 History: Received July 22, 2010; Accepted September 27, 2011; Published February 13, 2012; Online February 13, 2012

Carbon nanotube- or/and graphite-filled polymer composites were synthesized by using simple mixing and drying methods, and their thermal conductivities and structures were characterized by using a steady-state method (ASTM D5470) and scanning and transmission electron microscopies. In order to investigate the influence of synthesis conditions on the thermal conductivity of composites, various concentrations of multiwall carbon nanotubes, graphites, surfactants, and polymer matrix materials as well as two different nanoparticles and solvents were tested. Our composites containing both nanotubes (25 wt. %) and graphites (25 wt. %) with sodium dodecyl benzene sulfonate (SDBS) as a dispersant showed the highest thermal conductivity, ∼1.8 W/m-K at room temperature. The highest conductivity from nanotube/graphite mixtures would be from good adhesion and less voids between nanotubes and polymers as well as excellent thermal conduction from graphite sheets. The thermal conductivities of the composites have been calculated as a function of carbon nanotube concentrations by using a model based on the Maxwell’s effective medium theory, and the most effective method of improving thermal conductivity was suggested.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The thermal conductivities of samples 1–8 at room temperature. MW, Vin, and Gra represent MWCNT, Vinnapas 401, and graphite, respectively. The inset shows X-ray diffraction of nickel-decorated nanotubes.

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Figure 2

(a) Iron-incorporated nanotubes and (b) nickel-incorporated nanotubes before they were mixed into polymers. Black circular shape objects are the metal nanoparticles. Both scale bars indicate 100 nm.

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Figure 3

Room temperature thermal conductivities (samples 7 and 9–11) as a function of four different weight ratios (1:0, 4:1, 1:1, and 1:4) of graphites to MWCNTs. The composites contain total 50-wt. % fillers and 25-wt. % surfactant.

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Figure 4

The cold-fractured cross-sectional surfaces of (a) sample 7 (50-wt. % graphites) and (b) sample 10 (25-wt. % graphites and 25-wt. % MWCNTs). The inset show a nanotube bundle between graphite sheets. Scale bars indicate 5 μm except the inset scale bar (2 μm).

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Figure 5

The thermal conductivities of samples 8 and 12–18 at room temperature. For samples 12–18, nanotubes and graphites were dispersed in DMF or NMP without using any stabilizers such as SDBS or SDS.

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Figure 6

The cold-fractured cross-sectional surfaces of (a) sample 15 (dispersant: DMF) and (b) sample 16 (dispersant: NMP). The inset in (a) shows nanotube bundles between graphite sheets. Scale bars indicate 5 μm except the inset scale bar (2 μm).

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Figure 7

Room temperature thermal conductivities of samples 7, 19, 10, and 20 to find the influence of polymer matrices (EPON vs Vinnapas) on the thermal conductivity of the composites. The inset shows a fractured surface of sample 20. The scale bar indicates 5 μm.

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Figure 8

(a) Calculated thermal conductivities for the graphite-filled composites. The solid line represents calculated thermal conductivities from Eq. 3 with α = 4.97. The experimental thermal conductivities for sample 6 (hollow circle), sample 7 (hollow triangle), and sample 8 (hollow square) were used for finding α. ke (fgraphite ) in Eq. 5 for sample 9 (green filled diamond), sample 10 (red filled circle), and sample 11 (blue filled triangle) were obtained from Eq. 3. (b) Calculated thermal conductivities for sample 9 (green dash line), 10 (red solid line), 11 (blue dashed-dotted line), and 20 (black dotted line) obtained by using Eq. 5. Experimental data for sample 9 (green filled diamond), sample 10 (red filled circle), sample 11 (blue filled triangle), and sample 20 (black hexagon) were plotted together and used for finding β.

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