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.

Using density functional theory calculations (both perturbed and unperturbed) as well as thermodynamic and ballistic transport equations, what follows investigates thermal and mechanical properties of 2D boron monolayers (δ 6 -, α-, δ 5 -, and χ 3 -sheets with respective vacancy densities η = 0, 1/9, 1/7, 1/5) as they relate to the vacancy density. The triangular (δ 6 ) sheet's room-temperature phonon and electron thermal conductances are found to respectively be roughly 2.06 times and 6.60 times greater than those of PACS numbers: 65.40.-b, 62.20.-x, 63.22.-m

We present a comprehensive computational study on the properties of facecentered cubic and hexagonal chalcogenide Ge 2 Sb 2 Te 5 . We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, also looking suitable for transport analysis. Optical constants including refraction index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the band gap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches ∼ 1.4 × 10 6 J/(m 3 K) at high temperature, in agreement with experimental data, and provides insight into the low-temperature range (< 150 K), where data are unavailable.

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