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Research Papers: Conduction

The Influence of Carbon Nanotube Aspect Ratio on Thermal Conductivity Enhancement in Nanotube–Polymer Composites

[+] Author and Article Information
Rahul S. Kapadia

e-mail: rskapadi@ucsd.edu

Brian M. Louie

e-mail: bmlouie@ucsd.edu

Prabhakar R. Bandaru

Professor
e-mail: pbandaru@ucsd.edu
Department of Mechanical Engineering,
University of California,
San Diego, CA 92093

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received February 28, 2013; final manuscript received July 9, 2013; published online October 25, 2013. Assoc. Editor: Oronzio Manca.

J. Heat Transfer 136(1), 011303 (Oct 25, 2013) (6 pages) Paper No: HT-13-1106; doi: 10.1115/1.4025047 History: Received February 28, 2013; Revised July 09, 2013

We report and model a linear increase in the thermal conductivity (κ) of polymer composites incorporated with relatively low length/diameter aspect ratio multiwalled carbon nanotubes (CNTs). There was no evidence of percolation-like behavior in the κ, at/close to the theoretically predicted threshold, which was attributed due to the interfacial resistance between the CNT and the polymer matrix. Concomitantly, the widely postulated high thermal conductivity of CNTs does not contribute to the net thermal conductivity of the composites. Through estimating the interfacial resistance and the thermal conductivity of the constituent CNTs, we conclude that our experimental and modeling approaches can be used to study thermal transport behavior in nanotube–polymer composites.

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Figures

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Fig. 1

Scanning electron microscope (SEM) image indicating uniform dispersion of MWCNTs in polymer matrix

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Fig. 2

Schematic representation of experimental setup for the thermal conductivity (κ) measurement of the nanotube–polymer composite. The heat flux, (q), was deduced from the TC recordings in the top and bottom stainless steel bars. Typical values of average heat flux (qavg) observed was ∼3500 W/m2.

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Fig. 3

Experimentally measured values of κcomp with increasing volume fraction of CNTs. Circle symbols denote the values for composites with MWCNTs of AR = 35, while the star symbols denote the values for composites with MWCNTs of AR = 70.

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Fig. 4

A unit cell of a CNT with surrounding interface layer was used as a constituent to model the nanotube–polymer composite

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Fig. 6

Equivalent circuit model for thermal transport in a nanotube–polymer composite. The top branch indicates the two interfaces in series with a CNT, while the bottom branch models heat flow through the polymer matrix.

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Fig. 5

Modeling κcomp, using κCNT as a fitting parameter. Circle symbols indicate experimental values for composites constituted of MWCNTs with an average AR of 35.

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Fig. 9

Modeled κcomp increase showing effect of increasing diameter, d of MWCNT (L is constant). Square symbols indicate experimental data for composites with constituent MWCNT fillers of average AR of 35, while star symbols indicate experimental data for composites with constituent MWCNT fillers of average AR of 70.

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Fig. 8

Modeled κcomp increase, showing effect of increasing length, L of MWCNT (d is constant). Triangle symbols indicate experimental data for composites with constituent MWCNT fillers of average AR of 70.

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Fig. 7

Ratio of the thermal resistance from the nanotube and two interfaces: (Rtotal) to the interfacial resistance, (Rint), as a function of the intrinsic thermal conductivity of the CNT: κCNT

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