Research Papers

Synthesis and Characterization of Solid-State Phase Change Material Microcapsules for Thermal Management Applications

[+] Author and Article Information
Fangyu Cao

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20740
e-mail: fycao@umd.edu

Jing Ye

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20740
e-mail: ppsi523@gmail.com

Bao Yang

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20740
e-mail: baoyang@umd.edu

1Corresponding author.

Manuscript received October 2, 2013; final manuscript received February 25, 2014; published online March 12, 2014. Assoc. Editor: Calvin Li.

J. Nanotechnol. Eng. Med 4(4), 040901 (Mar 12, 2014) (5 pages) Paper No: NANO-13-1070; doi: 10.1115/1.4026970 History: Received October 02, 2013; Revised February 25, 2014

Polyalcohols such as neopentyl glycol (NPG) undergo solid-state crystal transformations that absorb/release significant latent heat. These solid–solid phase change materials (PCM) can be used in practical thermal management applications without concerns about liquid leakage and thermal expansion during phase transitions. In this paper, microcapsules of NPG encapsulated in silica shells were successfully synthesized with the use of emulsion techniques. The size of the microcapsules range from 0.2 to 4 μm, and the thickness of the silica shell is about 30 nm. It was found that the endothermic phase transition of these NPG-silica microcapsules was initiated at around 39 °C and the latent heat was about 96.0 J/g. A large supercooling of about 43.3 °C was observed in the pure NPG particles without shells, while the supercooling of the NPG microcapsules was reduced to about 14 °C due to the heterogeneous nucleation sites provided by the silica shell. These NPG microcapsules were added to the heat transfer fluid PAO to enhance its heat capacity and the effective heat capacity of the fluid was increased by 56% with the addition of 20 wt. % NPG-silica microcapsules.

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Fig. 1

Process of synthesizing NPG in silica microcapsules. (a) Mixing water phase into cyclohexane with surfactant; (b) adding TEOS to the mixture; (c) hydrolysis of TEOS to form silica shell; and (d) collection of microcapsules.

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Fig. 2

(a) SEM and (c) TEM images of as-synthesized microcapsules of NPG in silica shell, and (b) SEM and (d) TEM images of wrinkled silica shell after NPG is removed. Inserted in (a) is a histogram of the particle size distribution of the NPG-silica microcapsules.

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Fig. 3

FT-IR spectra of sample (a) silica, (b) NPG, and (c) NPG-silica microcapsules

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Fig. 4

Atomic distribution of the NPG-silica microcapsules measured using the EDS technique

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Fig. 5

DSC heating and cooling curves of samples, (a) pure, bulk NPG, (b) dispersions of pure NPG micro-particles in PAO, and (c) dispersions of 20 wt. % NPG-silica microcapsules in PAO

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Fig. 6

Calculated effective heat capacity of dispersion of NPG particles and dispersions of NPG-silica microcapsules

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Fig. 7

Dynamic viscosities of pure PAO and PAO containing 20 wt. % microcapsules in versus temperature



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