Segregated-network polymer nanocomposites for thermoelectric energy conversion
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Polymers are intrinsically poor thermal conductors, which are ideal for thermoelectrics, but low electrical conductivity (σ) and Seebeck coefficient (S) have excluded them as feasible candidates for thermoelectric applications. By adding single-walled carbon nanotubes (SWNT) to a polymer emulsion, a set of polymer nanocomposites that exhibit true thermoelectric behavior (i.e., generate electricity via a thermal gradient) have been created. As the polymer emulsion is drying, the relatively large polymer particles (100 - 1000+ nm) force the nanotubes to reside in the interstitial space between them. This creates a segregated network of carbon nanotubes with high electrical conductivity. This high electrical conductivity is accompanied by low thermal conductivity (k ∼ 0.35 W/m-K). Electrical conductivity is further increased (> 300 S/cm with 20 wt% SWNT) when the nanotubes are stabilized in water using intrinsically-conductive poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) [PEDOT-PSS]. At the present time, segregated network composites are being produced with a thermoelectric figure of merit (ZT = S 2σ/k) greater than 0.02 at room temperature, which is among the highest values ever reported for an all-carbon thermoelectric material. Further work with these nanocomposites is expected to result in low cost, easy to process polymer-based devices capable of converting waste heat to useful energy.
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