Mixtures of poly(3, and polystyrenesulfonate (PEDOT:PSS) have high electrical conductivity when cast from aqueous suspensions in combination with a high boiling-point cosolvent dimethyl sulfoxide (DMSO). The electronic component of the thermal conductivity of these highly conducting polymers is of interest for evaluating their potential for thermoelectric cooling and power generation. We find, using time-domain thermoreflectance measurements of thermal conductivity along multiple directions of thick (>20 μm) drop-cast PEDOT films, that the thermal conductivity can be highly anisotropic (Λ ∥ ≈ 1.0 W m −1 K −1 and Λ ⊥ ≈ 0.3 W m −1 K −1 for the in-plane and throughplane directions, respectively) when the electrical conductivity in the in-plane direction is large (σ ≈ 500 S cm −1 ). We relate the increase in thermal conductivity to the estimated electronic component of the thermal conductivity using the Wiedemann−Franz law, and find that our data are consistent with conventional Sommerfeld value of the Lorenz number. We use measurements of the elastic constants (C 11 ≈ 11 GPa and C 44 ≈ 17 GPa) of spin-cast PEDOT films and through-plane thermal conductivity (Λ ⊥ ≈ 0.3 W m −1 K −1 ) of drop-cast and spin-cast films to support our assumption that the phonon contribution to the thermal conductivity does not change significantly with DMSO composition.

Polymers have many desirable properties for engineering systems−e.g., low mass density, chemical stability, and high strength-to-mass ratio−but applications of polymers in situations where heat transfer is critical are often limited by low thermal conductivity. Here, we leverage the enormous research and development efforts that have been invested in the production of high-modulus polymer fibers to advance understanding of the mechanisms for thermal transport in this class of materials. Time-domain thermoreflectance (TDTR) enables direct measurements of the axial thermal conductivity of a single polymer fiber over a wide temperature range, 80 < T < 600 K. Relaxation of thermoelastic stress in the Al film transducer has to be taken into account in the analysis of the TDTR data when the laser spot size is small because the radial modulus of the fiber is small. This stress relaxation is controlled by the velocity of the zero-order symmetric Lamb mode of a thin Al plate. We find similarly high thermal conductivities of Λ ≈ 20 W m −1 K −1 in crystalline polyethylene and liquid crystalline poly(p-phenylene benzobisoxazole). For both fiber types, Λ(T) ∝ 1/T near room temperature, suggesting an intrinsic limit to the thermal conductivity governed by anharmonicity, not structural disorder. Because of the high degree of elastic anisotropy, longitudinal acoustic phonons with group velocities directed along fiber axis are likely to be the dominate carriers of heat.

This contribution reports a series of anionic narrow-band-gap self-doped conjugated polyelectrolytes (CPEs) with π-conjugated cyclopenta-[2,1-b;3,4-b']-dithiophene-alt-4,7-(2,1,3-benzothiadiazole) backbones, but with different counterions (Na(+), K(+), vs tetrabutylammonium) and lengths of alkyl chains (C4 vs C3). These materials were doped to provide air-stable, water-soluble conductive materials. Solid-state electrical conductivity, thermopower, and thermal conductivity were measured and compared. CPEs with smaller counterions and shorter side chains exhibit higher doping levels and form more ordered films. The smallest countercation (Na(+)) provides thin films with higher electrical conductivity, but a comparable thermopower, compared to those with larger counterions, thereby leading to a higher power factor. Chemical modifications of the pendant side chains do not influence out of plane thermal conductivity. These studies introduce a novel approach to understand thermoelectric performance by structural modifications.

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Near-field thermal radiation can be several orders of magnitude higher than that between two black bodies. Previous studies have shown that the energy transfer between two semi-infinite media separated by a nanometre vacuum gap is maximized when the real part of the dielectric function is around −1 due to the excitement of surface waves. Real materials can exhibit such a behaviour only within a very small spectral interval. However, by tuning the different adjustable parameters of the dielectric functions, it is possible to estimate the maximum achievable near-field radiative transfer. In this study, the influence of each parameter in the Drude and the Lorentz models on the nanoscale radiation is investigated. Optimal values are obtained for these parameters that maximize the near-field heat flux, which can be more than an order of magnitude higher than previously calculated values for SiC and doped Si. The effect of temperature on the optimal parameters in the Drude model is also discussed. The results will guide future selection and design of materials for the enhancement in near-field heat transfer.