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Research Papers: Micro/Nanoscale Heat Transfer

Effect of Particle Size and Aggregation on Thermal Conductivity of Metal–Polymer Nanocomposite

[+] Author and Article Information
Xiangyu Li

School of Mechanical Engineering;Birck Nanotechnology Center,
Purdue University,
West Lafayette, IN 47907
e-mail: li1215@purdue.edu

Wonjun Park

School of Electrical and Computer Engineering;Birck Nanotechnology Center,
Purdue University,
West Lafayette, IN 47907
e-mail: wjpark249@gmail.com

Yong P. Chen

Department of Physics and Astronomy;Birck Nanotechnology Center;School of Electrical and Computer Engineering,
Purdue University,
West Lafayette, IN 47907
e-mail: yongchen@purdue.edu

Xiulin Ruan

School of Mechanical Engineering;Birck Nanotechnology Center,
Purdue University,
West Lafayette, IN 47907
e-mail: ruan@purdue.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 23, 2016; final manuscript received August 21, 2016; published online October 11, 2016. Assoc. Editor: Alan McGaughey.

J. Heat Transfer 139(2), 022401 (Oct 11, 2016) (5 pages) Paper No: HT-16-1103; doi: 10.1115/1.4034757 History: Received February 23, 2016; Revised August 21, 2016

Metal nanoparticle has been a promising option for fillers in thermal interface materials due to its low cost and ease of fabrication. However, nanoparticle aggregation effect is not well understood because of its complexity. Theoretical models, like effective medium approximation model, barely cover aggregation effect. In this work, we have fabricated nickel–epoxy nanocomposites and observed higher thermal conductivity than effective medium theory predicts. Smaller particles are also found to show higher thermal conductivity, contrary to classical models indicate. A two-level effective medium approximation (EMA) model is developed to account for aggregation effect and to explain the size-dependent enhancement of thermal conductivity by introducing local concentration in aggregation structures.

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Figures

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Fig. 1

In-phase and out-of-phase 3ω signals (hollow circles and squares) are fitted with analytical solution (solid line and dashed line) to obtain thermal conductivity of Ni–epoxy nanocomposites

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Fig. 2

TEM figures of nanocomposites with 40 nm and 70 nm nickel particles are taken at the same magnification, scale bar set as 5 μm for (a) and (b). A more spread-out aggregation structure is observed in nanocomposites with smaller particle size than that in larger one at similar concentrations.

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Fig. 3

Thermal conductivities of Ni–epoxy composites with different particle sizes and concentrations are compared with the Maxwell model. All thermal conductivities are higher than the Maxwell model, and smaller particles yield higher thermal conductivities than larger ones. (a) Nanocomposite with 40 nm Ni at 5.74% and (b) nanocomposite with 70 nm Ni at 5.52%.

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Fig. 4

Two-level EMA model applied two different EMA models to calculate thermal conductivities of the clusters (level 1) and the overall composite (level 2)

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Fig. 5

Sintering effect is observed in nanocomposite with 40 nm Ni at 5.74%. Lines are labeled where a continuous path is formed among nanoparticles. The scale bar is set as 200 nm.

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Fig. 6

Local concentration of Ni particles in aggregations is plotted with different overall concentrations and nickel particle sizes

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