Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also compared with the newest model. The obtained results show potential for application of the graphene nanocomposites for electrical insulation with enhanced thermal conductivity. This paper also presents and discusses the unique temperature dependencies of thermal conductivity in a wide temperature range, significant for full understanding thermal transport mechanisms.

The efficient management of heat is a key issue when considering the performance of electrical devices. To reduce the probability of their failure an effective heat dissipation should be ensured. The thermal conductivity of pure epoxy is low and can be improved through the addition of fillers. Graphene has been considered as an adequate filler, due to its excellent thermal conductivity. However, graphene‐based composites also show a high electrical conductivity, which limits their application as an electrical insulation considerably. The presented work shows that it is possible to enhance thermal conductivity through the incorporation of a new class of hybrid filler, namely a masterbatch of graphene nanoplatelets (GNPs) and a standard filler like silica. This unique structural design combines the advantages of both, GNPs and silica powder, resulting in composites that not only show high thermal conductivity, but also preserve electrical insulation functionality. A modified processing method leads to the improvement of thermal conductivity. GNPs‐silica hybrid epoxy composites with only 2 wt% of GNPs reached 1.54 W/mK, whereas the volume resistivity remained at the level of 1015 Ω cm. The unique scientific aspect, namely temperature dependence of thermal conductivity, was studied. The presented novel hybrid composites show great potential in applications requiring electrical insulation with enhanced thermal conductivity in high voltage devices. POLYM. COMPOS., 39:E1682–E1691, 2018. © 2017 Society of Plastics Engineers

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Molybdenum disulfide (MoS2) polycrystalline thin films of different thicknesses have been deposited by radio frequency magnetron sputtering and then post-annealed. The resonant and non-resonant Raman spectra consist of broadened, insignificantly shifted peaks, pointing out that the atomic structure of MoS2 in thin films is preserved. X-ray diffraction and high-resolution transmission electron microscopy suggest that the mean crystallite size of MoS2 thin films ranges from 2.8 to 4.2 nm with increasing film thickness. The blue shift in the optical absorption spectra with the decreasing mean crystallite size and decreasing layer thickness provides tailorability of the bandgap. The increase in the effective bandgap from 1.6 to 1.9 eV is apparent with the reduction in film thickness from 24 to 1.5 nm. It can be seen that even for thick films, whose thickness can be compared to the bulk sample, the value of the effective bandgap is higher than 1.2 eV, as reported for bulk MoS2. It is presumed that this effect could be attributed to the quantum size effect exerted by two types of energy barriers: grain boundaries and layer surfaces. The experimentally measured bandgap of MoS2 thin films is compared with the predictions of the effective mass approximation and the hyperbolic band approximation models for the crystallites building up the films.