Three-Dimensional Printing to Fabricate Graphene-Modified Polyolefin Elastomer Flexible Composites with Tailorable Porous Structures for Electromagnetic Interference Shielding and Thermal Management Application

Revolutionary communication technologies including 5G and their correlated microelectronic equipment have generated the new generation of electronic components with a higher power density, which not only would bring electromagnetic waves (EMWs) radiation pollution but also would produce a lot of waste heat problems. In order to satisfy the requirements of advanced electronic components for the multifunctionality, light weight, flexibility, and complex structure, in this work, the polyolefin elastomer (POE)/graphene nanoplatelets (GNPs) nanocomposites with tailorable porous structures were successfully prepared through effectively combining the ultrasonic dispersion strategy with the fused deposition modeling (FDM) 3D printing technology. The results show that the synergistic effect of the constructed GNP network structure and the FDM printed porous structure could effectively enhance the electromagnetic shielding (EMI SE) performance of the 3D printed parts and meet their increasing demands for thermal management. When the content of the incorporated GNPs is 10.93 vol %, the EMI shielding efficiency (SE) value of the printed part could be up to 35 dB, and the value of the thickness-normalized specific SE (SSE/t) under the best printing conditions (50% infill density) could reach up to 244.9 dB·cm2/g. In addition, the achieved maximum thermal conductivity is 4.3 W/(m·K), which is 1600% higher than that of the pure POE matrix. The excellent flexibility of the printed pad also ensures its good contact with the electronic device during operation. Finally, the COMSOL simulation results verify the application feasibility of the FDM printed part. This work provides a novel strategy for preparation of customizable and multifunctional porous flexible parts, which is expected to be applied in the field of microelectronics such as communication intelligent devices

EPR and Rheological Study of Hybrid Interfaces in Gold–Clay–Epoxy Nanocomposites

With the aim to obtain new materials with special properties to be used in various industrial and biomedical applications, ternary “gold–clay–epoxy” nanocomposites and their nanodispersions were prepared using clay decorated with gold nanoparticles (AuNPs), at different gold contents. Nanocomposites structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Rheology and electron paramagnetic resonance (EPR) techniques were used in order to evaluate the molecular dynamics in the nanodispersions, as well as dynamics at interfaces in the nanocomposites. The percolation threshold (i.e., the filler content related to the formation of long-range connectivity of particles in the dispersed media) of the gold nanoparticles was determined to be ϕ_p = 0.6 wt % at a fixed clay content of 3 wt %. The flow activation energy and the relaxation time spectrum illustrated the presence of interfacial interactions in the ternary nanodispersions around and above the percolation threshold of AuNPs; these interfacial interactions suppressed the global molecular dynamics. It was found that below ϕ_p the free epoxy polymer chains ratio dominated over the chains attracted on the gold surfaces; thus, the rheological behavior was not significantly changed by the presence of AuNPs. While, around and above ϕ_p, the amount of the bonded epoxy polymer chains on the gold surface was much higher than that of the free chains; thus, a substantial increase in the flow activation energy and shift in the spectra to higher relaxation times appeared. The EPR signals of the nanocomposites depended on the gold nanoparticle contents and the preparation procedure thus providing a fingerprint of the different nanostructures. The EPR results from spin probes indicated that the main effect of the gold nanoparticles above ϕ_p, was to form a more homogeneous, viscous and polar clay–epoxy mixture at the nanoparticle surface. The knowledge obtained from this study is applicable to understand the role of interfaces in ternary nanocomposites with different combinations of nanofiller