Thermal management materials for energy-efficient and sustainable future buildings

Nanoscale hyperthermia mesostructures for sustainable antimicrobial design

Sustainability is critical in addressing global challenges posed by prolonged pandemics that impact health, economies, and the environment. Here, we introduce a molecular engineering approach for thermoregulated antimicrobial management inspired by firewalking rituals. The study uses in situ spectroscopy and multi-scale modeling to validate a hierarchical design. Efficient light-to-thermal energy conversion is achieved by engineering the molecular band structure. Rapid nanoscale hyperthermia is facilitated through thermal engineering. This approach significantly reduces the half-life of pathogens such as Escherichia coli, influenza A, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to 1.4 min while maintaining a low perceived temperature on human skin. Standard disease infection and epidemic models show this technology's potential to flatten outbreak curves and delay peak infection rates, which is crucial during the early stages of pandemics when developing vaccines and antiviral drugs takes time. The scalable manufacturing and broad antimicrobial applicability hold great promise for controlling emerging infectious diseases and diverse bioprotective applications.

Electrically gated molecular thermal switch

Controlling heat flow is a key challenge for applications ranging from thermal management in electronics to energy systems, industrial processing, and thermal therapy. However, progress has generally been limited by slow response times and low tunability in thermal conductance. In this work, we demonstrate an electronically gated solid-state thermal switch using self-assembled molecular junctions to achieve excellent performance at room temperature. In this three-terminal device, heat flow is continuously and reversibly modulated by an electric field through carefully controlled chemical bonding and charge distributions within the molecular interface. The devices have ultrahigh switching speeds above 1 megahertz, have on/off ratios in thermal conductance greater than 1300%, and can be switched more than 1 million times. We anticipate that these advances will generate opportunities in molecular engineering for thermal management systems and thermal circuit design.

Non-Perturbative Determination of Isotope-induced Anomalous Vibrational Physics

In general, vibrational physics has been well described by quantum perturbation theory to provide footprint characteristics for common crystals. However, despite weak phonon anharmonicity, the recently discovered cubic crystals have shown anomalous vibrational dynamics with elusive fundamental origin. Here, we developed a non-perturbative ab initio approach, in together with spectroscopy and high-pressure experiments, to successfully determine the exact dynamic evolutions of the vibrational physics for the first time. We found that the local fluctuation and coupling isotopes significantly dictate the vibrational spectra, through the Brillouin zone folding that has been previously ignored in literature. By decomposing vibrational spectra into individual isotope eigenvectors, we observed both positive and negative contributions to Raman intensity from constitutional atoms (10B, 11B, 75As or 31P). Importantly, our non-perturbative theory predicts that a novel vibrational resonance appears at high hydrostatic pressure due to broken translational symmetry, which was indeed verified by experimental measurement under a pressure up to 31.5 GPa. Our study develops fundamental understandings for the anomalous lattice physics under the failure of quantum perturbation theory and provides a new approach in exploring novel transport phenomena for materials of extreme properties.

Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures and high stability for thermal insulation

Cellulose-based, closed-cell porous materials templated from emulsions are promising for thermal insulation, but their low stability imposed by physical interaction hinders the materials from real applications. Herein, we report the fabrication of cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures, high stability and flexibility for thermal insulation. The polyHIPEs were prepared from cellulose-stabilized Pickering high internal phase emulsions through interfacial crosslinking using isocyanate. The resulting polyurethane polyHIPEs showed controllable external shapes, quasi-closed-cell structures, high flexibility, low density, and robust compression (without fracture even after compression to 30 % original height). The crosslinking enabled the polyHIPEs to show hydrophobicity, good stability (without breakage and dissolution observed after immersing in NaOH solution at pH 12, HCl solution at pH 1 and hot water at 100 °C, for 24 h) and decreased moisture uptake (below 1 %). The low density and quasi-closed-cell structures endowed the polyHIPEs with high thermal insulation, with thermal conductivity as low as 33.1 mW/(m K). These features make the cellulose-based, closed-cell polyHIPEs as an excellent candidate for thermal insulting.

Large Enhancement in Thermal Conductivity of Solvent-Cast Expanded Graphite/Polyetherimide Composites

We demonstrate in this work that expanded graphite (EG) can lead to a very large enhancement in thermal conductivity of polyetherimide-graphene and epoxy-graphene nanocomposites prepared via solvent casting technique. A k value of 6.6 W⋅m-1⋅K-1 is achieved for 10 wt% composition sample, representing an enhancement of ~2770% over pristine polyetherimide (k~0.23 W⋅m-1⋅K-1). This extraordinary enhancement in thermal conductivity is shown to be due to a network of continuous graphene sheets over long-length scales, resulting in low thermal contact resistance at bends/turns due to the graphene sheets being covalently bonded at such junctions. Solvent casting offers the advantage of preserving the porous structure of expanded graphite in the composite, resulting in the above highly thermally conductive interpenetrating network of graphene and polymer. Solvent casting also does not break down the expanded graphite particles due to minimal forces involved, allowing for efficient heat transfer over long-length scales, further enhancing overall composite thermal conductivity. Comparisons with a recently introduced effective medium model show a very high value of predicted particle-particle interfacial conductance, providing evidence for efficient interfacial thermal transport in expanded graphite composites. Field emission environmental scanning electron microscopy (FE-ESEM) is used to provide a detailed understanding of the interpenetrating graphene-polymer structure in the expanded graphite composite. These results open up novel avenues for achieving high thermal conductivity polymer composites.