Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self-assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum-assisted layerby-layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofibernanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4-20-fold increase of stiffness), light weight (density ≈1.01 g cm −3 ), dielectric stability over a broad range of temperature (25-200 °C) and frequencies (10 3 -10 6 Hz), good dielectric breakdown strength (≈292 MV m −1 ), and excellent thermal management capability (about 5-24 times higher thermal conductivity) such as fast heat dissipation.

The 3-Omega measurement technique was applied to a microbridge heater for the purpose of low power gas sensing. The sensor performance was evaluated for mixtures of CO 2 , Ar, He and CH 4 in N 2 in an isothermal chamber where concentrations were precisely controlled by mass flow controllers. A custom 3-Omega conditioning circuit controls the AC heating current and detection of the 3-Omega voltage signal. The amplitude and phase lag, and the in-phase and outof-phase components of the 3-Omega signal are presented for each case and are related directly to gas concentrations. Advantageously, the phase lag can determine the gas concentration without calibration of an individual gas sensor. Using this technique and our current microbridge thermal conductivity detector (TCD), it is possible to resolve gas concentrations down to 0.07%. The frequency behavior of the 3-Omega signal as it pertains to the thermal environment and sensor sensitivity is discussed. The 3-Omega technique combined with the microbridge is capable of operating with power consumptions that are < 10 % of the power consumed by conventional Wheatstone bridge measurements at room temperature.

Thermal conductivity in polymers has been theoretically and experimentally studied in good detail, but there is a need for more accurate models. Polymeric thermal conductivity exhibits a plateau‐like transition at temperatures around 10 K, which is not well accounted for by existing models. In this work, an empirical model that can predict temperature‐dependent thermal conductivity of amorphous polymers is developed. The model is based on kinetic theory and accounts for three sets of vibrational modes in polymers, and is developed using classical expressions, results of previous simulations, and experimental data. Fundamental material properties like density, monomer molecular weight, and speed of sound are the only input parameters. The model provides estimates for the locations of transitions between different sets of vibrational modes, an upper limit for the thermal conductivity, and temperature‐dependent thermal conductivity, which are in good agreement with experimental data. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1160–1170

Anisotropic thermal conductivity can complicate the performance of semiconducting polymer thin-films in applications such as thermoelectrics and photovoltaics. Anisotropic measurements of low thermal conductivity polymers are challenging, and there are a limited number of appropriate measurement techniques. Suspended film 3-omega is an appropriate technique but has often required unfavorable microfabrication. Herein, we report on the utility of the suspended 3-omega technique that uses shadow masking, and no other microfabrication techniques, in performing anisotropic (in-plane and through-plane) thermal conductivity measurements of polymer films. We report on the necessary conditions for the validity of the 1D suspended-film heat transfer model and provide experimental guidelines for in-plane thermal conductivity measurements of polymer thin-films. Furthermore, for the first time, we report the anisotropic thermal conductivities of N2200 and a low molecular weight P3HT, which are two common n-type and p-type semiconducting polymers. Measured thermal conductivities are compared with predictions from the conventional Cahill-Pohl model and a recent empirical model that more accurately predicts the temperature dependence.

Organic thermoelectrics have witnessed rapid development in the past decade for low temperature energy harvesting applications. While high performance p-type polymers have been demonstrated, ntype materials have lagged behind due to the limited number of stable n-dopants and low doping efficiencies. Nickel-coordination polymers are a promising class of n-type polymers as they are conducting without extrinsic doping, thus overcoming a major challenge. However, advantages in thermoelectric properties are outweighed by a complicated synthesis and a poorly understood reaction mechanism that has resulted in a large variation in literature for the same material. This progress report provides a comprehensive and critical overview of syntheses and thermoelectric property optimization approaches for two coordination polymers, namely Ni-ethenetetrathiolate (NiETT) and Nitetrathiooxalate (NiTTO). In particular, material characterization and thin film fabrication techniques are discussed, and the importance of reporting statistically relevant thermoelectric properties is highlighted to ensure reproducibility among different groups. A short discussion on prototype devices based on NiETT is presented, and finally, directions for future development of these and other n-type metal-coordinated polymers are suggested.