Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily ...processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti₃C₂Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti₃C₂Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti₃C₂Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.
Metal-coated polymer bead based composites are promising as electromagnetic interference (EMI) shielding and thermally conductive materials because they form a percolation 3D metal shell network at ...very low filler content. Herein, we fabricated 3D Cu/Ag shell network composites through electroless plating of metal on polymer beads and a simple hot pressing technique. Cu and Ag shells provide a continuous network for electron and heat conduction; thus, yielding excellent EMI shielding effectiveness of 110 dB at a 0.5 mm thickness and a thermal conductivity of 16.1 W m−1K−1 at only 13 vol % of metal filler. The properties of composites depend on the size of polystyrene (PS) beads and large size metal-coated PS bead composites exhibit higher electrical conductivity, EMI shielding effectiveness, and thermal conductivity than small size bead composites. These results are ascribed to the reduction in the number of contact interfaces between metal-coated beads, which minimizes the interfacial resistance. This study is set to pave the way for designing advanced EMI shielding and thermal conductive materials by a scalable and efficient synthesis approach.
In this work, for the first time we fabricated highly self-aligned large-area reduced graphene oxide/poly (vinylidene fluoride-co-hexafluoropropylene) (rLGO/PVDF-HFP) composite films through simple ...solution casting followed by low temperature chemical reduction process. The resulting free-standing rLGO/PVDF-HFP composite thin film revealed excellent electrical conductivity of ∼3000 S/m and ultrahigh in-plane thermal conductivity of ∼19.5 W/mK at rLGO content of 27.2 wt %. This ultrahigh electrical and thermal conductivity were attributed to the good interfacial interaction, effective chemical reduction, high aspect ratio, and preferential orientation of graphene sheets along the film direction. We believe that our new fabrication procedure can be effectively used for large-scale production and commercialization of conductive composite materials for many thermal and electrical conduction applications.
We prepared poly(vinylidene fluoride) (PVDF)/multiwalled carbon nanotube (MWCNT) nanocomposites using the electrospinning process and investigated the effects of varying the MWCNT content, as well as ...the additional use of drawing and poling on the polymorphic behavior and electroactive (piezoelectric) properties of the membranes obtained. Fourier transform infrared spectroscopy and wide-angle X-ray diffraction revealed that dramatic changes occurred in the β-phase crystal formation with the MWCNT loading. This was attributed to the nucleation effects of the MWCNTs as well as the intense stretching of the PVDF jets in the electrospinning process. The remanent polarization and piezoelectric response increased with the amount of MWCNTs and piezoelectric β-phase crystals. A further mechanical stretching and electric poling process induced not only highly oriented β-phase crystallites, but also very good ferroelectric and piezoelectric performances. In the drawn samples, the interfacial interaction between the functional groups on the MWCNTs and the CF2 dipole of PVDF chains produced a large amount of β-phase content. In the poled samples, the incorporation of the MWCNTs made it easy to obtain efficient charge accumulation in the PVDF matrix, resulting in the conversion of the α-phase into the β-phase as well as the enhancement of remanent polarization and mechanical displacement.
Thermally curable hybrid ionogel electrolytes consisting of epoxy-functionalized POSS, amine-terminated polypropylene glycol, and ionic liquid electrolyte, 1M LiTFSI in BMPTFSI were fabricated to ...give ionic conducting epoxy networks with cubic inorganic star networks crosslinked with lithium ion dissociating polypropylene glycol linkers. Characterization of these hybrid ionogels revealed high ion conduction, exceptional thermal stability, and electrochemical stability. Lithium ion capacitors fabricated with these hybrid ionogels revealed exceptional performance on par with the neat liquid ionic liquid electrolyte, and far superior over ionogels fabricated with conventional organic crosslinkers, due to the mechanical robustness and lithium ion dissociative character imparted by the POSS and PPG functionalities.
•Hybrid ionogel electrolytes with POSS epoxy networks were fabricated.•Quasi solid state behavior was confirmed through rheological analysis.•High ion conduction, good thermal and electrochemical stability were observed.•Lithium ion capacitors fabricated with hybrid ionogels revealed good performance.
Electrically conductive thin carbon materials have attracted remarkable interest as a shielding material to mitigate the electromagnetic interference (EMI) produced by many telecommunication devices. ...Herein, we developed a sulfur-doped reduced graphene oxide (SrGO) with high electrical conductivity through using a novel biomass, mushroom-based sulfur compound (lenthionine) via a two-step thermal treatment. The resultant SrGO product exhibited excellent electrical conductivity of 311 S cm–1, which is 52% larger than 205 S cm–1 for undoped rGO. SrGO also exhibited an excellent EMI shielding effectiveness of 38.6 dB, which is 61% larger than 24.4 dB measured for undoped rGO. Analytical examinations indicate that a sulfur content of 1.95 atom % acts as n-type dopant, increasing electrical conductivity and, therefore, EMI shielding of doped graphene.
Design of materials to be heat-conductive in a preferred direction is a crucial issue for efficient heat dissipation in systems using stacked devices. Here, we demonstrate a facile route to fabricate ...polymer composites with directional thermal conduction. Our method is based on control of the orientation of fillers with anisotropic heat conduction. Melt-compression of solution-cast poly(vinylidene fluoride) (PVDF) and graphene nanoflake (GNF) films in an L-shape kinked tube yielded a lightweight polymer composite with the surface normal of GNF preferentially aligned perpendicular to the melt-flow direction, giving rise to a directional thermal conductivity of approximately 10 W/mK at 25 vol % with an anisotropic thermal conduction ratio greater than six. The high directional thermal conduction was attributed to the two-dimensional planar shape of GNFs readily adaptable to the molten polymer flow, compared with highly entangled carbon nanotubes and three-dimensional graphite fillers. Furthermore, our composite with its density of approximately 1.5 g/cm3 was mechanically stable, and its thermal performance was successfully preserved above 100 °C even after multiple heating and cooling cycles. The results indicate that the methodology using an L-shape kinked tube is a new way to achieve polymer composites with highly anisotropic thermal conduction.
•HDPE/silane-treated boron nitride (mBN) composites were fabricated.•The HDPE/mBN composites revealed a strong adhesion behavior at the interface of matrix/filler.•The HDPE/mBN composites show ...superior radiation shielding, thermoconductive and mechanical properties to the composites containing pristine BN and B4C fillers.
High-density polyethylene (HDPE) composites with modified boron nitride (mBN) fillers, functionalized with an organosilane, were fabricated through conventional melt-extrusion processing techniques. The properties and performances of these composites were compared with those of the composites containing pristine BN and boron carbide (B4C) fillers. The silane functionalization of the BN fillers strongly improved the interfacial adhesion between the polymer matrix and the filler. As a result, the HDPE/mBN composites showed a better dispersion state of the filler particles, larger tensile modulus, greater effective thermal conductivity, and better neutron shielding property compared with the HDPE/BN and HDPE/B4C composites.
Lithium pre-doping of graphite anode is a key process to achieve high energy density lithium-ion capacitor. In this study, in situ synchrotron wide-angle X-ray scattering examinations directly ...revealed that the direct contact (DC) method, simply achieved through direct physical contact between graphite electrode and sacrificial lithium metal in electrolyte, provides much faster phase transformation from stage 1ʹ to stage 1 than conventional electronic charger (EC) and external short circuit (ESC) methods at the same doping time level. The observations indicate that DC method achieves faster pre-lithiation rate of graphite electrode than EC and ESC processes.
•Phase transformation of graphite was characterized by in situ X-ray scattering.•Direct contact between graphite and lithium metal leads fast lithiation.•The direct contact method is a robust pre-doping process without any safety issues.•The study provides an alternative pre-doping method for Li-ion capacitors.
A novel ionic mixture of an imidazolium‐based room‐temperature ionic liquid containing ethylene‐oxide‐functionalized phosphite anions is fabricated, which, when doped with lithium salt, ...self‐assembles into a smectic‐ordered ionic liquid crystal through Coulombic interactions between the ion species. Interestingly, the smectic order in the ionic‐liquid‐crystal ionogel facilitates ionic transport.
