Search

Polymers, with various advantages including lightweight, low cost, flexibility and ease of processing, are popular choices for thermal management in flexible electronics, photovoltaics, fuel cells, etc. In this perspective, we review the recent progress of developing uniaxial thermally conductive polymers and three-dimensional polymers with high thermal conductivity, discuss new opportunities in applying machine learning methods to search for thermally conductive polymers, and finally point out current key challenges and future directions in simulations and experimental measurements. The useful insights in this perspective can guide the rational design of thermally conductive polymers for advanced thermal management.

Polymers, with various advantages including lightweight, low cost, flexibility and ease of processing, are popular choices for thermal management in flexible electronics, photovoltaics, fuel cells, etc. In this perspective, we review the recent progress of developing uniaxial thermally conductive polymers and three-dimensional polymers with high thermal conductivity, discuss new opportunities in applying machine learning methods to search for thermally conductive polymers, and finally point out current key challenges and future directions in simulations and experimental measurements. The useful insights in this perspective can guide the rational design of thermally conductive polymers for advanced thermal management. This paper delineates the advantages and recent progress of pristine polymers with high thermal conductivity and provides significant insights on future directions in the simulations and experimental measurements of thermally conductive pristine polymers. [ABSTRACT FROM AUTHOR]

Summary: Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. [ABSTRACT FROM AUTHOR]

Thermally conductive polymer matrix composites (PMC) are promising alternatives to traditional electronic packaging materials to enhance the heat dissipation of integrated circuits, due to polymer's superior electrical insulating property, low cost, and light weight. This work aims to investigate the potentials of using synergy effects of hexagonal boron nitride (hBN) platelets and spherical hBN particulates or those of hBN platlets with bimodal size distribution to promote PMC's effective thermal conductivity ( k eff ). PMC consists of polybutylene terephthalate (PBT) and hBNs with different geometries and size distributions were used as case examples. Experimental results reveal that PMC filled with solely hBN spherical agglomerates of fine diameters possess the highest k eff , owing to its isotropic thermal conductivity and compact filler-filler interaction. Moreover, two-dimensional hBN platelets, which have anisotropic thermal conductivity, of bimodal size distribution show synergistic effect on PMC's k eff . To maximize PMC's k eff with a minimum filler loading, an optimal mixture of hBN platelets with bimodal size distribution would help to overcome the trade-off between enhanced filler networking and increased thermal contact resistance at the filler-filler interfaces. The findings in this study provide some insights to design and fabricate thermally conductive PMC with reduced filler loading for thermal management applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] BN, talc and TiO2 in 30vol% were compounded with polypropylene matrix. [•] According to the DSC measurements, the fillers are good nucleating agents. [•] The thermal conductivity of the fillers influences the cooling rate of the melt. [•] The higher the cooling rate is, the lower the crystallinity in the polymer matrix. [Copyright &y& Elsevier]

Common polymers are thermal insulators. Turning polymer insulators into heat conductors is of fundamental interest and technological importance. Thermally conductive polymers may replace traditional metal heat conductors as lightweight and corrosion-resistant heat dissipators. In this review, we highlight recent progresses in developing polymers with metal-like thermal conductivity and discuss the understanding of thermal transport mechanisms in polymers. We use polyethylene as a model and address how thermal conductivity of polyethylene is influenced by structural parameters such as bond strength, chain orientation, molecular weight, crystallinity, and crystallite size. We review advanced strategies for developing thermally conductive polymers, e.g., mechanical stretching, extrusion, electrospinning, and template-assisted methods. We highlight how thermally conductive polymers provide new possibilities for future thermal management applications. Finally, we discuss future challenges and opportunities in designing and synthesizing polymers with metal-like thermal conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Different types of graphene-related materials (GRM) are industrially available and have been exploited for thermal conductivity enhancement in polymers. These include materials with very different features, in terms of thickness, lateral size and composition, especially concerning the oxygen to carbon ratio and the possible presence of surface functionalization. Due to the variability of GRM properties, the differences in polymer nanocomposites preparation methods and the microstructures obtained, a large scatter of thermal conductivity performance is found in literature. However, detailed correlations between GRM-based nanocomposites features, including nanoplatelets thickness and size, defectiveness, composition and dispersion, with their thermal conductivity remain mostly undefined. In the present paper, the thermal conductivity of GRM-based polymer nanocomposites, prepared by melt polymerization of cyclic polybutylene terephtalate oligomers and exploiting 13 different GRM grades, was investigated. The selected GRM, covering a wide range of specific surface area, size and defectiveness, secure a sound basis for the understanding of the effect of GRM properties on the thermal conductivity of their relevant polymer nanocomposites. Indeed, the obtained thermal conductivity appeares to depend on the interplay between the above GRM feature. In particular, the combination of low GRM defectiveness and high filler percolation density was found to maximize the thermal conductivity of nanocomposites. [ABSTRACT FROM AUTHOR]

• Liquid metal interconnects encapsulated with a high thermal conductivity elastomer. • Flexible, body-worn thermoelectric generators with best-in-class performance. • Highest reported power density > 35 μW/cm2 from body heat harvesting. • First flexible thermoelectric generator that has the potential to rival rigid TEGs. This paper reports flexible thermoelectric generators (TEGs) employing eutectic gallium indium (EGaIn) liquid metal interconnects encased in a novel, high thermal conductivity (HTC) elastomer. These TEGs are part of a broader effort to harvest thermal energy from the body and convert it into electrical energy to power wearable electronics. The flexible TEGs reported in this paper employ the same thermoelectric legs' used in rigid TEGs, thus eliminating the need to develop new materials specifically for flexible TEGs that often sacrifice the so-called figure of merit' for flexibility. Flexible TEGs reported here embed rigid thermoelectric legs' in soft and flexible packaging, using stretchable EGaIn interconnects. The use of liquid metal interconnects provides ultimate stretchability and low electrical resistance between the thermoelectric legs. The liquid metal lines are encased in a new stretchable silicone elastomer doped with both graphene nano-platelets and EGaIn to increase its thermal conductivity. This high thermal conductivity elastomer not only reduces the parasitic thermal resistance of the encapsulation layer but it also serves as a heat spreader, leading to 1.7X improvement in the output power density of TEGs compared to devices fabricated with a conventional elastomer. The device performance is further improved by a thin Cu layer acting as a heat spreader providing an additional 1.3X enhancement in the output power at 1.2 m/s air velocity (typical walking speed). Worn on the wrist, our best devices achieve power levels in excess of 30 μW/cm2 at an air velocity of 1.2 m/s outperforming previously reported flexible TEGs. [ABSTRACT FROM AUTHOR]