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.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

Electromagnetic interference shielding effectiveness of carbon materials

IO N The rapid development of modern electronics packed with highly integrated circuits generates severe electromagnetic radiation, which leads to harmful effects on highly sensitive precision electronic equipment as well as the living environment for human beings. Great effort has been made for the development of high-performance electromagnetic interference (EMI) shielding materials. In addition to high EMI shielding performance, being lightweight and fl exible are two other important technical requirements for effective and practical EMI shielding applications especially in areas of aircraft, aerospace, automobiles, and fast-growing next-generation fl exible electronics such as portable electronics and wearable devices. [ 1 ] Recently, electrically conductive polymer composites have received much attention for EMI shielding applications, [ 1–12 ] because of their light weight, resistance to corrosion, fl exibility, good processability, and low cost compared to the conventional metal-based materials. The EMI shielding effectiveness of the polymer composites depends critically on the intrinsic electrical conductivity, dielectric constant, magnetic permeability, aspect ratio, and content of conductive fi llers. [ 1–12 ] It is believed that high electrical conductivity and connectivity of the conductive fi llers can improve EMI shielding performance. [ 1 , 2 , 4 , 7 , 8 ]

Lightweight and Flexible Graphene Foam Composites for High‐Performance Electromagnetic Interference Shielding

A novel carbon nanotube-polystyrene foam composite has been fabricated successfully. The electromagnetic interference (EMI) shielding effectiveness measurements indicated that such foam composites can be used as very effective, lightweight shielding materials. The correlation between the shielding effectiveness and electrical conductivity and the EMI shielding mechanism of such foam composites are also discussed.

Novel carbon nanotube-polystyrene foam composites for electromagnetic interference shielding.

Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

Highly aligned graphene/polymer nanocomposites with excellent dielectric properties for high-performance electromagnetic interference shielding.

The processing of nickel filaments of 0.4 Μm diameter gives polyethersulfone-matrix composites with high electromagnetic interference shielding effectiveness, high reflection coefficient and low surface impedance at 1-2 GHz. With 7 vol.% nickel filaments, the composite exhibited shielding effectiveness 87 dB (compared to 90 dB for solid copper), surface impedance 1.2 Ω (same as for solid copper), tensile strength 52 MPa, modulus 5 GPa, ductility 1.0%, and density 1.87 g/cm3.

Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness

Nickel filaments of 0.4 μm diameter gave polyethersulfone-matrix composites with high electromagnetic interference shielding effectiveness and low surface impedance at 1–2 GHz. With 7 vol.% nickel filaments, the composite exhibited shielding effectiveness 87 dB (compared to 90 dB for solid copper), surface impedance 1.2 Ω (same as for solid copper), tensile strength 52 MPa, modulus 5 GPa, ductility 1.0% and density 1.87 g/cm3. The low surface impedance is valuable for microwave waveguides.

A material including filaments, which include a metal and an essentially coaxial core, each filament having a diameter less than 6 μm, each core being essentially carbon, displays high effectiveness for shielding electromagnetic interference (EMI) when dispersed in a matrix to form a composite material. This matrix is selected from the group consisting of polymers, ceramics and polymer-ceramic combinations. This metal is selected from the group consisting of nickel, copper, cobalt, silver, gold, tin, zinc, nickel-based alloys, copper-based alloys, cobalt-based alloys, silver-based alloys, gold-based alloys, tin-based alloys and zinc-based alloys. The incorporation of 7 percent volume of this material in a matrix that is incapable of EMI shielding results in a composite that is substantially equal to copper in EMI shielding effectiveness at 1-2 GHz.

Metal filaments for electromagnetic interference shielding

The relationship between strain and the fractional increase in electrical resistance of piezoresistive polyether-sulfone-matrix composite strain sensors was found to be much more linear and less noisy when the electrically conducting filler was 0.1 m diameter carbon filaments rather than the conventionally used 10 m diameter carbon fibers. For the fiber composite, the non-linearity manifested itself as increasing reversibly with increasing compressive strain - an effect opposite to and occurring on top of piezoresistivity. This effect was absent from the filament composite. Furthermore, the percolation threshold was lower for the filament composite than for the fiber composite. For both filament and fiber composites, became more negative as cycling progressed up to 10 cycles and then stabilized though the effect was more significant for the latter.

https://iopscience.iop.org/article/10.1088/0964-1726/5/2/014/pdf

A piezoresistive carbon filament polymer-matrix composite strain sensor

Discontinuous nickel filaments of diameter 0.4 μm and having a carbon core of diameter 0.1 μm were fabricated by electroplating nickel on discontinuous carbon filaments. They exhibited a grain size of 0.016 μm and electrical resistivity of about 5 × 10−6 Ω·cm. In an amount as low as 7 vol.% in a polymer (polyether sulfone) matrix, they resulted in a composite exhibiting electromagnetic interference shielding effectiveness of 87 dB and reflection coefficient 0.95 at 1–2 GHz, tensile strength 52 MPa, tensile ductility 1.0%, and density 1.87 g/cm3.

Xiaoping Shui

Papers

Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness

Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness

Metal filaments for electromagnetic interference shielding

A piezoresistive carbon filament polymer-matrix composite strain sensor

Submicron diameter nickel filaments and their polymer-matrix composites