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Steadily, continuously, and precisely adjusting infrared emissivity of materials is of great importance for various applications, such as thermal camouflage. Herein, a method is proposed to fine-tune the emissivity of multilayer graphene (MLG) by ion intercalation with assistance of pulse voltage. The dynamic ion intercalation process in MLG-based emissivity modulators is investigated by a home-made electrical-optical synchronizing test system, which consists of a potentiostat and a thermal camera. It is observed that the apparent temperature of MLG is closely correlated with pulse duration and residual charges. Based on a second-order RC model, the ion transportation and charge transfer in the modulator are likely affected by three factors (i.e., internal resistance, electric field, and concentration gradient), which changes the doping level of MLG. Hence, the emissivity of MLG can be finely adjusted by regulating the duration of the voltage pulse. This also leads to a wavelength dependence of emissivity modulation, which is confirmed by Fourier transform infrared spectroscopy. The observations offer a promising venue for precise and continuous adjustment of MLG's emissivity, which is of great significance for many practical applications, such as simulating complex and subtle thermal images. [ABSTRACT FROM AUTHOR]

Actively controlling the infrared emissivity of materials is critical for many applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown great potential as a functional material with a tunable infrared emissivity. However, the spatial homogeneity in adjusting MLG's emissivity through ion intercalation is rather poor, which limits its practical applications. Here, we study how mixing various molecular components (e.g., ethanol) with ionic liquids affects the performance of MLG-based infrared emissivity modulators. The results indicate that introducing a moderate concentration of molecular components not only significantly improves spatial homogeneity in tuning emissivity but also enhances modulation depth, dynamic response, and the stability of the modulators. This is likely due to the increasing conductivity of the mixture and the improved wetting properties between the mixture and the separator, which leads to more effective charge transfer from ions in ionic liquids to carbons in graphene. The microscopic structure of MLG, revealed by Raman spectroscopy, confirms that the improvement in modulator performance is mostly due to homogeneous transportation of ions in the modulators. This not only sheds light on the underlying physics of the modulator but also greatly expands the options when selecting ionic liquids, thereby opening a new route for the modulator design. [ABSTRACT FROM AUTHOR]

With the continuous advancement of electronic devices, there is an urgent need for advanced thermal interface materials (TIMs) to prevent high-power density electronics from overheating. The orderly arrangement of thermally conductive fillers in TIMs plays a crucial role in enhancing thermal conduction along preferred directions. However, it is challenging to control the orientation of the fillers, especially for two-dimensional fillers. In this study, graphene nanoplates (GNPs) were co-planarly arranged in polyvinyl alcohol (PVA) using a rotating magnetic field, which significantly increased the thermal conductivity of the composites. The coplanar vertically aligned GNPs/PVA (CVGNPs/PVA) exhibited a through-plane thermal conductivity of 11.78 W m−1 K−1, which is about 10 times higher than that of the composites with disorderly distributed GNPs (1.14 W m−1 K−1). The rotating magnetic field facilitated the alignment of GNPs and increased face-to-face contact between adjacent GNPs, which significantly boosted the through-plane thermal conductivity of the composite. The compressive modulus of the CVGNPs/PVA composites was only 1.06 MPa, and it helped to reduce the thermal interface resistance to 49 mm2 K W−1. These results offer a novel approach for preparing excellent TIMs that could be used in various applications. GNPs are oriented more compactly and orderly in PVA by using the rotating magnetic field, resulting in a densified thermal conductive paths and higher thermal conductivity of the composite. [Display omitted] [ABSTRACT FROM AUTHOR]

Currently, epoxy-based composites are widely used in thermal management. However, with the development of complex and high power-density electronic devices, the thermal properties of the composites need to be improved. Inspired by the unique galls-leaf structure of Distylium chinense, a graphene-diamond framework (GRDF) is developed by a simple filtration method. A through-plane and in-plane thermal conductivity of 22.7 and 21.8 Wm−1 K−1, respectively, have been achieved by forming epoxy-based composites with the GRDF annealed at 3000 °C. The result is 70% higher than the best-reported value for epoxy-based composites prepared by vacuum filtration under a filler content of 43 wt%. Such high thermal conductivity remains unchanged (within 2%) in a temperature range from 25 to 100 °C. Based on various microscopic characterizations, the diamond particles evenly distribute in a framework formed by graphene sheets, which bridge the gaps in the framework and improve its structural integrity. High-temperature annealing converts most diamond particles to graphite, which further enhances the thermal properties of the composite. The observations provide a feasible way for developing polymer-based composite with high thermal conductivity, which could meet the ever-increasing demands for heat dissipation in high-power electronics. [Display omitted] • The epoxy composite with a through-plane thermal conductivity of 22.7 Wm−1K−1 is achieved under 43.2 wt.% filler filling. • The composites show a high degree of isotropic thermal properties, and a good thermal stability. • The high thermal conductivity of the composite is due to diamond filling and high-temperature graphitization. [ABSTRACT FROM AUTHOR]

A review of carbon-based thermal interface materials: mechanisms, thermal measurements and thermal properties. [Display omitted] • Various carbon-based thermal interface materials were reviewed, ranging from one-dimensional carbon nanotubes, two-dimensional graphene films, to three-dimensional graphene foams, graphene aerogels, vertical graphene and other 3D graphene. • Thermal measurements for bulk and nanoscale materials were discussed to offer a guidance for improving the precision of the results. • The challenges for carbon-based thermal interface materials were discussed, including how to decrease the overall thermal resistance of thermal interface materials, the potential applications from micro to macro devices and the prerequisites for industrial application. With the development of electronic technologies, electronic devices become smaller, while their power density increases dramatically. The resulting excessive heat requires excellent heat dissipation to ensure great performance of the devices. A good thermal interface material (TIM), with excellent bulk thermal conductivity and proper elastic modulus, which can fill the gap between contact surfaces, is of great importance to improve overall performance of thermal management in the electronic devices. Carbon-based materials, such as carbon nanotubes (CNTs) and graphene (Gr), have attracted great attentions, due to their intrinsic high thermal conductivity. In this paper, carbon-based TIMs are reviewed, as well as the thermal conducting mechanisms and techniques to measure thermal properties for materials. The unique three-dimensional network of 3D-Gr provides not only high thermal conductivity, but also excellent mechanical properties, which makes it more competitive as TIM than CNTs and Gr. Furthermore, there is currently no universal characterization techniques, which are suitable to measure thermal properties of all TIMs. Hence, special attention must be paid to select a proper technique based on the measuring principle, in order to obtain accurate results. An outlook of the future challenges of the thermal interface materials is proposed at the end of the paper. [ABSTRACT FROM AUTHOR]