Pushing the Limits of Heat Conduction in Covalent Organic Frameworks Through High-Throughput Screening of Their Thermal Conductivity.

Tailor-made materials featuring large tunability in their thermal transport properties are highly sought-after for diverse applications. However, achieving `user-defined' thermal transport in a single class of material system with tunability across a wide range of thermal conductivity values requires a thorough understanding of the structure-property relationships, which has proven to be challenging. Herein, large-scale computational screening of covalent organic frameworks (COFs) for thermal conductivity is performed, providing a comprehensive understanding of their structure-property relationships by leveraging systematic atomistic simulations of 10,750 COFs with 651 distinct organic linkers.

Reversible and high-contrast thermal conductivity switching in a flexible covalent organic framework possessing negative Poisson's ratio.

The ability to dynamically and reversibly control thermal transport in solid-state systems can redefine and propel a plethora of technologies including thermal switches, diodes, and rectifiers. Current material systems, however, do not possess the swift and large changes in thermal conductivity required for such practical applications. For instance, stimuli responsive materials, that can reversibly switch between a high thermal conductivity state and a low thermal conductivity state, are mostly limited to thermal switching ratios in the range of 1.

Origin of Ultralow Thermal Conductivity in Metal Halide Perovskites.

Resulting from their remarkable structure-property relationships, metal halide perovskites have garnered tremendous attention in recent years for a plethora of applications. For instance, their ultralow thermal conductivities make them promising candidates for thermoelectric and thermal barrier coating applications. It is widely accepted that the "guest" cations inside the metal halide framework act as "rattlers", which gives rise to strong intrinsic phonon resistances, thus explaining the structure-property relationship dictating their ultralow thermal conductivities.

Direct Measurement of Ballistic and Diffusive Electron Transport in Gold.

We experimentally show that the ballistic length of hot electrons in laser-heated gold films can exceed ∼150 nm, which is ∼50% greater than the previously reported value of 100 nm inferred from pump-probe experiments. We also find that the mean free path of electrons at the peak temperature following interband excitation can reach upward of ∼45 nm, which is higher than the average value of 30 nm predicted from our parameter-free density functional perturbation theory. Our first-principles calculations of electron-phonon coupling reveal that the increase in the mean free path due to interband excitation is a consequence of drastically reduced electron-phonon coupling from lattice stiffening, thus providing the microscopic understanding of our experimental findings.

Tailoring the thermal conductivity of two-dimensional metal halide perovskites.

Proper thermal management of solar cells based on metal halide perovskites (MHPs) is key to increasing their efficiency as well as their durability. Although two-dimensional (2D) MHPs possess enhanced thermal stability as compared to their three-dimensional (3D) counterparts, the lack of comprehensive knowledge of the heat transfer mechanisms dictating their ultralow thermal conductivities is a bottleneck for further improvements in their thermal performance. Here, we experimentally and computationally study the Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) phases of MHPs ( = 1) to demonstrate that the length of the organic spacers has a negligible influence on their thermal transport properties; we experimentally measure thermal conductivities of 0.

Development and performance optimization of knitted antibacterial materials using polyester-silver nanocomposite fibres.

The development and performance optimization of knitted antibacterial materials made from polyester-silver nanocomposite fibres have been attempted in this research. Inherently antibacterial polyester-silver nanocomposite fibres were blended with normal polyester fibres in different weight proportions to prepare yarns. Three parameters, namely blend percentage (wt.