Nano Focus
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prepared co-extruded fibers using another adaptation of this technique. The researchers said that this new fabrication method will find increasing use to prepare ceramic and highly loaded ceramic/polymer nanocomposite fibers
from a variety of material combinations at low temperature and pressure with dimensions of 15–500 μm and controlled composition and microstructure. Kaushik Chatterjee
Nano Focus High thermoelectric efficiency achieved in polymer-nanocomposites
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esearchers R.A. Segalman (University of California, Berkeley and Lawrence Berkeley National Laboratories), J.J. Urban (Lawrence Berkeley National Laboratories), A. Majumdar (Advanced Research Projects Agency– Energy), and their co-workers have reported the highest thermoelectric figure of merit for an organic–inorganic hybrid or aqueously processed material to date. Thermoelectric efficiency is related to a combination of high thermopower (or Seebeck coefficient, S, V/K), high electrical conductivity (σ, S/cm), and low thermal conductivity (κ, W/m K). To date the best materials available have been inorganic compounds with relatively low earth abundance and highly complex processing routes (and hence greater expense), such as Bi2Te3. In the last decade, polymers with much enhanced electrical conductivities (>100 S/cm) have become common, and work on molecular junctions indicate that the organic–inorganic interface can provide a boost to Seebeck coefficient. As reported in the October 5th online edition of Nano Letters (DOI: 10.1021/nl102880k), the researchers combine a high electrical conductivity, low thermal conductivity polymer with a nanoparticle that contributes high thermopower. Additionally, the work functions of the two materials could be well aligned which opens the possibility of thermionic filtering at the interface and an additional boost to the power factor. In this case, the nanoparticle is composed of tellurium with a very high thermopower
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MRS BULLETIN
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VOLUME 35 • DECEMBER 2010
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Na2TeO3 Asc. Acid ∆ H2O
Dropcast
Water Soluble Rods
Insulating substrate
(a) Synthesis of PEDOT:PSS passivated Te nanorods and (b) dropcast composite film on a 1 cm2 quartz substrate, showing excellent film uniformity. Reproduced with permission from Nano Letters (2010) DOI: 10.1021/nl102880k. © 2010 American Chemical Society.
(~400 μV/K), but relatively low electrical conductivity and high thermal conductivity. The research team has shown that Te nanorods can be synthesized in situ into a highly electrically conductive, thermally insulating polymer (PEDOT: PSS, σ >100 S/cm, κ ~ 0.2W/m2 K) in a water solution (see figure). Suspended polymer coated rods can then be dropcast to form a smooth, conformal film. This film has an electrical conductivity two orders of magnitude higher than the Te nanowires and similar to a pure sample of the polymeric component at greater than 10 S/cm. The thermal conductivity for the hybrid is on the order of 0.2 W/(m K), comparable to the polymeric component. The Seebeck coefficient of the hybrid was 163 μV/K. Thermoe
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