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Reversible temperature regulation of electrical and thermal conductivity using liquid-solid phase transitions.

Zheng R, Gao J, Wang J, Chen G - Nat Commun (2011)

Bottom Line: Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature.With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C.The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

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Microstructures of graphite/hexadecane suspensions.(a) Optical microscope image of the microstructure of a 0.2% (volume fraction) graphite/hexadecane suspension; scale bar, 200 μm. The inset shows an optical photograph of a 50-ml, 0.2% graphite/hexadecane suspension after 3 months on the shelf. (b) A scanning electron micrograph of graphite flakes obtained by the H2SO4 intercalation, microwave expansion and ultrasonic exfoliation of natural graphite; scale bar, 1 μm. (c) A typical transmission electron microscopy image of a graphite flake. The inset shows a high-resolution transmission electron microscopy image of the selected area (denoted by A). Scale bar in c and inset correspond to 1 μm and 5 nm, respectively. (d) C1s X-ray photoelectron spectra of graphite flakes; the spectra have a main peak at 284.5 eV. The peak can be fit to peaks at 284.5, 285.6, 287.0 and 289.6 eV and thus assigned to the C=C, C−OH, C=O and O=C−OH species, respectively. (e) An optical microscope image of 0.05% graphite/hexadecane suspension. (f) An image of a frozen graphite/hexadecane composite. The black area represents graphite clusters, whereas the needle-like structure represents hexadecane grains. (g) The microstructure of a remelted graphite suspension showing the graphite percolation network. Scale bars in e, f and g are all corresponding to 200 μm.
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f1: Microstructures of graphite/hexadecane suspensions.(a) Optical microscope image of the microstructure of a 0.2% (volume fraction) graphite/hexadecane suspension; scale bar, 200 μm. The inset shows an optical photograph of a 50-ml, 0.2% graphite/hexadecane suspension after 3 months on the shelf. (b) A scanning electron micrograph of graphite flakes obtained by the H2SO4 intercalation, microwave expansion and ultrasonic exfoliation of natural graphite; scale bar, 1 μm. (c) A typical transmission electron microscopy image of a graphite flake. The inset shows a high-resolution transmission electron microscopy image of the selected area (denoted by A). Scale bar in c and inset correspond to 1 μm and 5 nm, respectively. (d) C1s X-ray photoelectron spectra of graphite flakes; the spectra have a main peak at 284.5 eV. The peak can be fit to peaks at 284.5, 285.6, 287.0 and 289.6 eV and thus assigned to the C=C, C−OH, C=O and O=C−OH species, respectively. (e) An optical microscope image of 0.05% graphite/hexadecane suspension. (f) An image of a frozen graphite/hexadecane composite. The black area represents graphite clusters, whereas the needle-like structure represents hexadecane grains. (g) The microstructure of a remelted graphite suspension showing the graphite percolation network. Scale bars in e, f and g are all corresponding to 200 μm.

Mentions: An optical microscope image of 0.2% (volume fraction) graphite/hexadecane suspension is shown in Figure 1a, together with an inset showing a photo of 50 ml of such a suspension after 3 months on the shelf. The graphite suspension is stable and no sediment is found. The graphite flakes have an average diameter of several microns and a thickness from several nanometres to several tens of nanometres (Fig. 1b). Because of the intrinsic stress induced during preparation, most of the graphite flakes are bent, with some of them even rolled up (Fig. 1c). A high-resolution transmission electron microscopy image (inset in Fig. 1c) of a selected flake shows that the flake has ~30 atomic layers with an interplanar distance of 0.335 nm, consistent with graphite7. We measured the mobility of graphite flakes in hexadecane to be ~0.03 cm2 V−1 s−1, which means that the graphite flakes are charged in hexadecane. X-ray photon spectroscopy (XPS) analysis indicates that the surface of the graphite flakes contains ~8% oxygen atoms (Fig. 1d), which are contributed by the hydroxyl, epoxide and carboxyl groups on the graphite surface. These functional groups may have a significant role in the stability of the graphite suspensions1213.


Reversible temperature regulation of electrical and thermal conductivity using liquid-solid phase transitions.

Zheng R, Gao J, Wang J, Chen G - Nat Commun (2011)

Microstructures of graphite/hexadecane suspensions.(a) Optical microscope image of the microstructure of a 0.2% (volume fraction) graphite/hexadecane suspension; scale bar, 200 μm. The inset shows an optical photograph of a 50-ml, 0.2% graphite/hexadecane suspension after 3 months on the shelf. (b) A scanning electron micrograph of graphite flakes obtained by the H2SO4 intercalation, microwave expansion and ultrasonic exfoliation of natural graphite; scale bar, 1 μm. (c) A typical transmission electron microscopy image of a graphite flake. The inset shows a high-resolution transmission electron microscopy image of the selected area (denoted by A). Scale bar in c and inset correspond to 1 μm and 5 nm, respectively. (d) C1s X-ray photoelectron spectra of graphite flakes; the spectra have a main peak at 284.5 eV. The peak can be fit to peaks at 284.5, 285.6, 287.0 and 289.6 eV and thus assigned to the C=C, C−OH, C=O and O=C−OH species, respectively. (e) An optical microscope image of 0.05% graphite/hexadecane suspension. (f) An image of a frozen graphite/hexadecane composite. The black area represents graphite clusters, whereas the needle-like structure represents hexadecane grains. (g) The microstructure of a remelted graphite suspension showing the graphite percolation network. Scale bars in e, f and g are all corresponding to 200 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f1: Microstructures of graphite/hexadecane suspensions.(a) Optical microscope image of the microstructure of a 0.2% (volume fraction) graphite/hexadecane suspension; scale bar, 200 μm. The inset shows an optical photograph of a 50-ml, 0.2% graphite/hexadecane suspension after 3 months on the shelf. (b) A scanning electron micrograph of graphite flakes obtained by the H2SO4 intercalation, microwave expansion and ultrasonic exfoliation of natural graphite; scale bar, 1 μm. (c) A typical transmission electron microscopy image of a graphite flake. The inset shows a high-resolution transmission electron microscopy image of the selected area (denoted by A). Scale bar in c and inset correspond to 1 μm and 5 nm, respectively. (d) C1s X-ray photoelectron spectra of graphite flakes; the spectra have a main peak at 284.5 eV. The peak can be fit to peaks at 284.5, 285.6, 287.0 and 289.6 eV and thus assigned to the C=C, C−OH, C=O and O=C−OH species, respectively. (e) An optical microscope image of 0.05% graphite/hexadecane suspension. (f) An image of a frozen graphite/hexadecane composite. The black area represents graphite clusters, whereas the needle-like structure represents hexadecane grains. (g) The microstructure of a remelted graphite suspension showing the graphite percolation network. Scale bars in e, f and g are all corresponding to 200 μm.
Mentions: An optical microscope image of 0.2% (volume fraction) graphite/hexadecane suspension is shown in Figure 1a, together with an inset showing a photo of 50 ml of such a suspension after 3 months on the shelf. The graphite suspension is stable and no sediment is found. The graphite flakes have an average diameter of several microns and a thickness from several nanometres to several tens of nanometres (Fig. 1b). Because of the intrinsic stress induced during preparation, most of the graphite flakes are bent, with some of them even rolled up (Fig. 1c). A high-resolution transmission electron microscopy image (inset in Fig. 1c) of a selected flake shows that the flake has ~30 atomic layers with an interplanar distance of 0.335 nm, consistent with graphite7. We measured the mobility of graphite flakes in hexadecane to be ~0.03 cm2 V−1 s−1, which means that the graphite flakes are charged in hexadecane. X-ray photon spectroscopy (XPS) analysis indicates that the surface of the graphite flakes contains ~8% oxygen atoms (Fig. 1d), which are contributed by the hydroxyl, epoxide and carboxyl groups on the graphite surface. These functional groups may have a significant role in the stability of the graphite suspensions1213.

Bottom Line: Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature.With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C.The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

Show MeSH
Related in: MedlinePlus