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 present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated. Simply via physical compression, the microwave absorption performance can be tuned. The qualified bandwidth coverage of 93.8% (60.5 GHz/64.5 GHz) is achieved for the GF under 90% compressive strain (1.0 mm thickness). This mainly because of the 3D conductive network.

Broadband and Tunable High‐Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam

https://cyberleninka.org/article/n/768408.pdf

Mechanical properties of graphene and graphene-based nanocomposites

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

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.

Monolayer graphene oxide (GO) sheets with sizes ranging from a few to ∼200 μm are synthesized based on a chemical method and are sorted out to obtain four different grades having uniform sizes. Transparent conductive films are produced using the ultralarge graphene oxide (UL-GO) sheets that are deposited layer-by-layer on a substrate using the Langmuir-Blodgett (LB) assembly technique. The density and degree of wrinkling of the UL-GO monolayers are turned from dilute, close-packed flat UL-GO to graphene oxide wrinkles (GOWs) and concentrated graphene oxide wrinkles (CGOWs) by varying the LB processing conditions. The method demonstrated here opens up a new avenue for high-yield fabrication of GOWs or CGOWs that are considered promising materials for hydrogen storage, supercapacitors, and nanomechanical devices. The films produced from UL-GO sheets with a close-packed flat structure exhibit exceptionally high electrical conductivity and transparency after thermal reduction and chemical doping treatments. A remarkable sheet resistance of ∼500 Ω/sq at 90% transparency is obtained, which outperforms the graphene films grown on a Ni substrate by chemical vapor deposition. The technique used in this work to produce transparent conductive UL-GO thin films is facile, inexpensive, and tunable for mass production.

Transparent Conductive Films Consisting of Ultralarge Graphene Sheets Produced by Langmuir–Blodgett Assembly

Fragmentation of plastic debris and the commercial use of plastic microbeads have led to the widespread distribution of microplastics in natural environments. Several studies have reported on the occurrence and toxicity of microplastics in soils and waters; however, because of methodological challenges, the presence and impact of nanoplastics (<100 nm) in natural systems have been largely ignored. Microbeads used in consumer products such as scrubs and shampoos are processed by mechanical means that may lead to their fragmentation into potentially more hazardous nanoplastics. In this study, three commercial facial scrubs containing polyethylene microbeads (∼0.2 mm diameter) were examined to verify whether they contained nanoplastics. Particulates in the scrubs were fractionated using sequential filtration to isolate <100 nm particles. Scanning electron microscopy was used to confirm the presence of nanoparticles ranging in size from 24 ± 6 to 52 ± 14 nm. X-ray photoelectron spectroscopy and Fourier transf...

http://pubs.acs.org/doi/pdf/10.1021/acs.estlett.7b00187

Are There Nanoplastics in Your Personal Care Products

This study demonstrates that large-size graphene oxide (GO) sheets can impart a tremendous positive impact on self-alignment, electrical conductivity, and mechanical properties of graphene papers. There is a remarkable, more than 3-fold improvement in electrical conductivity of the papers made from ultralarge GO sheets (with an average area of 272.2 μm2) compared to that of the small GO counterpart (with an average area of 1.1 μm2). The corresponding improvements in Young’s modulus and tensile strength are equally notable, namely 320% and 280%, respectively. These improvements of bulk properties due to the large GO sheets are correlated to multiscale elemental and structural characteristics of GO sheets, such as the content of carboxyl groups on the GO edge, C/O ratio and Raman D/G-band intensity ratio of GO on the molecular-scale, and the degree of dispersion and stacking behavior of GO sheets on the microscale. The graphene papers made from larger GO sheets exhibit a closer-stacked structure and better ...

Fabrication of Highly-aligned, Conductive, and Strong Graphene Papers Using Ultralarge Graphene Oxide Sheets

Polyurethane (PU)-based composite films containing highly aligned graphene sheets are produced through an environmentally benign process. An aqueous liquid crystalline dispersion of graphene oxide (GO) is in situ reduced in PU, resulting in a fine dispersion and a high degree of orientation of graphene sheets. The PU particles are adsorbed onto the surface of the reduced graphene oxide (rGO), and the rGO sheets with a large aspect ratio of over 10 000 tend to self-align during the film formation when the graphene content is high enough, say more than 2 wt%. The resulting composites show excellent electrical conductivity with an extremely low percolation threshold of 0.078 vol%, which is considered one of the lowest values ever reported for polymer composites containing graphene. The electrical conductivity of the composites with high graphene contents presents significant anisotropy due to the preferential formation of conductive networks along the in-plane direction, another proof of the existence of the self-aligned, layered structure.

Nariman Yousefi

Papers

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

Transparent Conductive Films Consisting of Ultralarge Graphene Sheets Produced by Langmuir–Blodgett Assembly

Are There Nanoplastics in Your Personal Care Products

Fabrication of Highly-aligned, Conductive, and Strong Graphene Papers Using Ultralarge Graphene Oxide Sheets

Self-alignment and high electrical conductivity of ultralarge graphene oxide–polyurethane nanocomposites