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[Display omitted] Nanograins and pores, as two common microstructural defects, are capable to impede phonon transport. However, thus far, the stability of nanograins at elevated temperature and the feasibility of porosity in boosting the figure of merit ZT are still concerned in thermoelectrics. Herein, we report that a specifically designed microstructure mainly consisting of ultrafine grains within the nanocrystalline regime and randomly distributed pores in α-MgAgSb gives rise to an ultralow lattice thermal conductivity ∼0.46 W m−1 K−1 at 300 K that breaks the limit of the estimated minimum value. Associated with a slightly deteriorated electrical performance, an unprecedented performance, ZT ∼0.94 at 300 K and ZT ave ∼1.16, are realized. Benefiting from optimized α-MgAgSb in this work and Mg 3.2 (Bi, Sb) 2 material to fabricate a Peltier module, we can achieve a high maximum temperature difference ΔT max ∼52 K and a maximum coefficient of performance COP ∼8.3 at hot-side temperature T h = 300 K, outperforming these previously reported non-Bi 2 Te 3 modules. This is, to our knowledge, the first demonstration of high performance thermoelectric modules mediated by the utilization of ultrafine grains and nanoporous structures, which provides a swift pathway to accelerate the wide employment of thermoelectric cooling technology in modern society. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs) are the key to solving heat dissipation problems in high-power electrical equipment. TIMs with high thermal conductivity and low thermal contact resistance (TCR) will enhance interfacial heat transfer. In this work, a phase-change mediated graphene composite hydrogel with low TCR and high thermal conductivity is designed. In addition, by introducing the hydrogel cross-linked network into the phase change material, the phase change material leakage problem is effectively solved. The thermal conductivity of the phase change hydrogel is enhanced by 324% from 0.3 W m − 1 K − 1 to 1.23 W m − 1 K − 1 at a filling rate of 7 wt% of graphene. The effects of temperature and pressure on phase change composite hydrogels are investigated. When the temperature is increased from 50 °C to 80 °C, TCR decreases rapidly from 90 K ∙ c m 2 / W to 0.2–0.5 K ∙ c m 2 / W , which is attributed to the improved interfacial wettability mediated by the phase change. When the pressure is increased from 10 Psi to 50 Psi with 80 °C, TCR decrease from 20 K ∙ c m 2 / W to 0.5 K ∙ c m 2 / W , improving interfacial contact and enhancing interfacial heat transfer. Combining a hydrogel with a cross-linked structure with the phase change material resulted in an excellent encapsulation of the phase change material. The thermal management performance of the phase change hydrogel is evaluated using infrared thermography and shows good thermal response behavior as the temperature rose to 68.7 °C after 120 s of heating. The strategy of combining phase change materials with hydrogels will provide new ideas for the design of TIMs. [Display omitted] [ABSTRACT FROM AUTHOR]

With the booming development of electronic devices usually used in a dynamic working environment, there is an urgent need for thermal interface materials with low thermal contact resistance, high thermal conductivity, excellent elasticity, and self-healing properties. A novel thermal interface material is obtained by incorporating graphene into a polyacrylate-based double cross-linked hydrogel. The introduction of graphene into the hydrogel can improve the thermal conductivity of the thermal interface material and enhance the tensile properties of the hydrogel. The composite thermally conductive hydrogel has self-healing properties, precisely meeting the thermal interface material's dynamic working environment. Besides, the effects of pressure and temperature on the thermal contact resistance are investigated. When the pressure increases from 10 Psi to 50 Psi at 35 °C, the thermal contact resistance is reduced to 0.069 K ∙ cm 2/ W. Under certain pressure, the effect of temperature on the thermal contact resistance is minor. Overall, the thermal contact resistance remains low (0.5–0.9 K ∙ cm 2/ W). The composite hydrogel is demonstrated excellent thermal management performance under the combined effect of high thermal conductivity and low thermal contact resistance by steady-state thermal analysis simulations and infrared thermography. Highly elastic, self-healing, low thermal resistance composites will present ideas for further construction of new thermal interface materials. [ABSTRACT FROM AUTHOR]

Polycrystalline BAsx (x = 0.80–1.10) compounds with different boron-to-arsenic elemental molar ratios were synthesized by a high-pressure and high-temperature sintering method. Compared with other ambient-pressure synthesis methods, high pressure can significantly promote the reaction speed as well as the reaction yield. As the content of arsenic increases from x = 0.91 to 1.10, the thermal conductivity of BAsx gradually increases from 53 to 65 W⋅m−1⋅K−1. Furthermore, the temperature dependence of thermal conductivities of these samples reveals an Umklapp scattering due to the increasing phonon population. This work provides a highly efficient method for polycrystalline BAs synthesis. [ABSTRACT FROM AUTHOR]

The adjustable thermal conductivity and thermal contact resistance are the key ways to realize efficient thermal management of electronic devices. In this work, a low melting-point alloy/paraffin/olefin block copolymer thermal interface material with the above properties was designed and prepared. Low melting-point alloy and paraffin undergo phase transformation with the increase of temperature, resulting in the significant decrease of thermal contact resistance. Moreover, the liquid phase low melting-point alloy particles are connected to reconstruct an efficient heat conduction path, which enhances the thermal conductivity of composites. In addition, this paper studied the thermal conductivity of composites at two different temperatures (30 °C/50 °C) and the effect of temperature or pressure on the thermal contact resistance. Furthermore, the heat dissipation effect of composites was evaluated by infrared thermal imager. The results prove that the thermal conductivity of composites (90 wt% filler) increases from 0.99 W / m ⋅ K to 1.87 W / m ⋅ K as the temperature increases from 30 °C to 50 °C. The thermal contact resistance of composites (90 wt% filler) is reduced to 0.024 K ⋅ c m 2 / W (60 °C, 40 Psi). Moreover, the results of heat dissipation experiments also confirm that the thermal contact resistance decreases with the enhancement of temperature. Therefore, all the results indicate that the thermal conductivity and thermal contact resistance of composites can be adjusted by changing the temperature. [Display omitted] • A liquid metal/paraffin/olefin block copolymer thermal interface material with adjustable thermal conductivity is designed. • The thermal conductivity of composites increases from 0.99 W/m.k (30°C) to 1.87 W/m.k (50°C). • The thermal contact resistance of composites (90 wt% filler) is reduced to 0.024 K ⋅ c m 2 / W (60 °C, 40 Psi). • The heat dissipation effect of composites is evaluated by infrared thermal imager. [ABSTRACT FROM AUTHOR]

Reducing thermal contact resistance (TCR) is an important way to enhance heat dissipation of electronic devices. Elastomer is easy to deform, increase the contact area and reduce the TCR, but its wetting condition is not satisfying. In this work, a novel elastomeric thermal interface materials (TIMs) polyethylene glycol/unsaturated polyester resin/graphene (PEG/UPR/G) was designed and prepared. With the increase of temperature, PEG near surface of PEG/UPR/G was released due to phase transformation, and a thin molten layer would be attached to the surface. By this way, the micro bumps on the solid surface were all soaked by the thin layer of molten PEG, which greatly reduced the TCR. In addition, the effect of temperature and pressure on TCR of elastomeric PEG/UPR/G were studied. When the pressure increases from 10 Psi to 50 Psi (65 °C), TCR decreases from 11–14 K ∙ cm 2/ W to 2–4 K ∙ cm 2/ W. The TCR will be further reduced to 0.7–0.9 K ∙ cm 2/ W (75 °C) due to the phase transition of PEG. Moreover, the heat dissipation effect of PEG/UPR/G was evaluated by infrared thermal imager. These results demonstrate that the total thermal resistance is the decisive factor for the final steady-state temperature and the time of unsteady heat transfer. [ABSTRACT FROM AUTHOR]