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)

We review the present state of polymer nanocomposites research in which the fillers are single-wall or multiwall carbon nanotubes. By way of background we provide a brief synopsis about carbon nanotube materials and their suspensions. We summarize and critique various nanotube/polymer composite fabrication methods including solution mixing, melt mixing, and in situ polymerization with a particular emphasis on evaluating the dispersion state of the nanotubes. We discuss mechanical, electrical, rheological, thermal, and flammability properties separately and how these physical properties depend on the size, aspect ratio, loading, dispersion state, and alignment of nanotubes within polymer nanocomposites. Finally, we summarize the current challenges to and opportunities for efficiently translating the extraordinary properties of carbon nanotubes to polymer matrices in hopes of facilitating progress in this emerging area.

Polymer Nanocomposites Containing Carbon Nanotubes

A review of vapor grown carbon nanofiber/polymer conductive composites

A high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high-pressure solid-phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi-facet segregated architecture with rGO selectively located on the boundaries among PS multi-facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional-pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.

Structured Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

http://www.ppsconferences.org/public/abs_2011/56.pdf

Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate

Metal nanowire/polymer nanocomposites are advanced materials for electrically conductive applications. Metal nanowires have high surface area, high aspect ratios, and high electrical conductivity, which are critical for the synthesis of conductive polymer nanocomposites using extremely low amounts of conductive filler. In this work, lightweight, thin, and highly conductive copper nanowire/polystyrene nanocomposites were prepared using a novel method of nanocomposite preparation termed miscible solvent mixing and precipitation (MSMP). Suspensions of high aspect ratio copper nanowires were mixed with polystyrene solutions to produce polymer nanocomposites with segregated nanowire networks resembling cell-like structures. Highly electrically conductive networks of nanowires were obtained beyond a percolation threshold of ϕc = 0.67 vol% and percolated nanocomposites showed electrical conductivities up to 104 S m−1, which exceeds the conductivity range generally reported for carbon nanofiller-based nanocomposites. The significant potential of these nanocomposites for electrical applications like electromagnetic interference (EMI) shielding was further demonstrated. Metal nanowire/polymer nanocomposites sheets of 0.21 mm in thickness exhibited EMI SE of more than 20 dB for copper nanowire concentrations of only 1.3 vol%.

Highly electrically conductive and high performance EMI shielding nanowire/polymer nanocomposites by miscible mixing and precipitation

A highly conductive with exceptional electromagnetic interference (EMI) shielding capabilities copper nanowire (CuNW)/Polystyrene (PS) composite powder was formulated by solution processing. We used a dilution process where the conductive powder was then dry mixed with pure PS powder to prepare composites with lower CuNW concentration. The composite parts were prepared by compression molding. The electrical percolation threshold of the composite prepared by the dilution process followed by the compression molding was only 0.24 vol.% CuNW. Electron micrographs indicated that the conductive powder formed a segregated network within the polymer matrix. The EMI shielding effectiveness (SE) results showed that in the X-band frequency range, a 210 μm film made of PS composite containing 1.3 vol.% CuNW has an EMI SE of 27 dB and PS with 2.1 vol.% CuNW has an EMI SE of 35 dB. For 1.3 vol.% and 2.1 vol.% CuNW composites, contribution of absorption to the overall shielding was ∼54% of the overall EMI SE.

Copper nanowire/polystyrene nanocomposites: Lower percolation threshold and higher EMI shielding

Silver and copper nanowires have been synthesized using a scalable method of AC electrodeposition into porous aluminum oxide templates, which produces gram quantities of metal nanowires ca. 25 nm in diameter and up to 5 and 10 μm in length for Ag and Cu, respectively. The nanowires have been used to prepare polystyrene nanocomposites by solution processing. Electrical resistivity measurements performed on polymer nanocomposites containing different volume fractions of metal indicate that low percolation thresholds of nanowires are attained between compositions of 0.25 and 0.75 vol %.

Low Electrical Percolation Threshold of Silver and Copper Nanowires in Polystyrene Composites

Multigram quantities of Cu nanowires ca. 25 nm in diameter and µm in length have been produced by AC electrodeposition into porous aluminium oxide (PAO) templates. Multiple, large-area Al electrodes (5 × 11 cm or 10 × 25 cm) are anodized in parallel at 25.0 V in 0.3 M H2SO4(aq) using custom built baths. The pores are efficiently filled by applying 200 Hz sine waves at 10 Vrms between the anodized Al and Cu plate counter electrodes immersed in a 0.50 M CuSO4(aq) solution. Dissolution of the PAO template in 0.6 M H3PO4 to free the Cu nanowires results in significant coarsening of the nanowires, whereas dissolution of the PAO template in 1.0 M NaOH(aq) results in retention of the Cu nanowire diameters corresponding to the pore diameter of the PAO template. Liberated Cu nanowires were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy.

Genaro A. Gelves

Papers

Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate

Highly electrically conductive and high performance EMI shielding nanowire/polymer nanocomposites by miscible mixing and precipitation

Copper nanowire/polystyrene nanocomposites: Lower percolation threshold and higher EMI shielding

Low Electrical Percolation Threshold of Silver and Copper Nanowires in Polystyrene Composites

Multigram synthesis of copper nanowires using ac electrodeposition into porous aluminium oxide templates