Absorption-dominant Mechanism Research Articles

Hugely improved electromagnetic interference shielding and mechanical properties for UHMWPE composites via constructing an oriented conductive carbon nanostructures (CNS) networks

To address the practical application challenges of conductive polymer composites (CPCs) in portable electronics equipment, such as their low thermal conductivity (TC) and poor electromagnetic interference (EMI) shielding effectiveness (EMI SE), it is crucial to improve their TC, electrical conductivity(σ), and EMI SE of CPCs. In this work, we present a conducting composite made of ultrahigh molecular weight polyethylene (UHMWPE) and carbon nanostructures (CNS) with a unique segregated structure. This structure is achieved through a simple high-speed mechanical mixing and compression molding process. Microscopy characteristics demonstrated that both the matrix and segregated conductive network were in-situ oriented along the compress direction of UHMWPE granules under the static hot-pressing field. CNS are compacted together at the interface between UHMWPE granules to form an oriented and interconnected conductive pathways at low CNS loading levels. The resultant UHMWPE/CNS composites with 10 wt% CNS content exhibits excellent EMI shielding performance, with EMI SE of 60.7 dB (at X-band), high conductivity of 2.42 S/cm, and acceptable thermal conductivity of 0.7217 (W/m K). High EMI shielding performance and absorption dominant mechanism are beneficial from the unique segregated structure, and individual CNS coated UHMWPE granule are similar to an electromagnetic cage. Additionally, the ultimate tensile strength of the composite remains high at 37.6 MPa even at 10.0 wt% CNS loading, and it shows effective thermal stability. These properties are attributed to the strong interfacial bonding between CNS and UHMWPE. These materials have potential applications in efficient thermal management and EMI shielding for high-performance intelligent electrical devices.

Recyclable magnetic carbon foams possessing voltage-controllable electromagnetic shielding and oil/water separation

Lightweight carbon foams with high-performance electromagnetic interference (EMI) shielding have attracted extensive attentions. However, it is challenging for researchers to effectively regulate the EMI shielding of carbon foams independent on shield's thickness. Herein, we proposed a macroscopic magnetic carbon foams through a chemical engineering strategy under the synergies of nickel ion reduction and in-situ growth of carbon nanotubes on carbon frameworks derived from carbonized woods. The macroscopic magnetic carbon foams present high-performance EMI shielding with absorption-dominant mechanism, and the removal of oil pollutants for water purification. Magnetic properties favor the manipulation of oil absorption without direct mechanic contact. After burning, the magnetic carbon foams can be re-used in EMI shielding and oil absorbency. Furthermore, we used a novel electric voltage-driven strategy to upgrade EMI shielding performances of magnetic carbon foams. By the increase in applied voltages, the enhanced absorption-dominant EMI shielding and fast oil absorbency due to the decrease viscosity of crude oil could be simultaneously obtained. The strategy developed here may lead a new avenue toward the design of porous magnetic carbon foams with the enhanced voltage-driven multifunctionalities for practical applications.

Multilayer Structures of a Zn0.5Ni0.5Fe2O4-Reduced Graphene Oxide/PVDF Nanocomposite for Tunable and Highly Efficient Microwave Absorbers

Attenuating electromagnetic waves with an absorption-dominant mechanism is still an arduous challenge, despite the recent progress in fabricating advanced electromagnetic interference (EMI) shields. In this study, EMI shielding materials with an outstanding absorption performance were developed. As such, in the first step, we report a practical method for synthesizing magnetic Zn0.5Ni0.5Fe2O4 (ZnNiFe) nanoparticles. The magnetic hysteresis loop reveals that the synthesized magnetic nanoparticles are superparamagnetic with a saturation magnetization of 75.8 emu/g. Thereafter, we propose an EMI absorber using a multilayer assembly of polyvinylidene fluoride sheets containing low concentrations of reduced graphene oxide (rGO) and ZnNiFe. It is shown that the EMI shielding effectiveness increases from 23.93 to 29.05 dB, and the shielding by reflection decreases from 6.5 to 0.5 dB. This happens as the number of layers increases from two to nine at a fixed total thickness of 1.8 mm and filler loadings of 1 wt % rGO and 5 wt % ZnNiFe. More importantly, the nine-layer sample shows an absorption coefficient of A = 0.91, which translated into absorption of more than 91% of the incident wave. To the best of our knowledge, this is the highest ever reported absorbance for a polymer-based EMI shield. It is hypothesized that the superior absorbance of the nine-layer structure originates from (1) multiple internal reflections inside the shield due to the presence of numerous conductive layers and (2) supermagnetic properties of ZnNiFe nanoparticles, leading to enhanced magnetic loss.

Fabrication and characterization of PVC based flexible nanocomposites for the shielding against EMI, NIR, and thermal imaging signals

Polypyrrole (PPy) and barium hexaferrite (BaFe) were prepared successfully by chemical polymerization and co-precipitation method, respectively. Nanocomposites based on polyvinyl chloride (PVC) matrix with different compositions of PPy and BaFe were fabricated by solution casting method with 0.5 mm film thickness. The key application of these nanocomposites is the electromagnetic interference (EMI) shielding in microwave frequency (0.1 GHz-20 GHz) and infrared (IR) shielding in near-infrared (NIR) wavelength (700–2500 nm). The PPy effect on electrical conductivity was measured and the results showed an increase in electrical conductivity by increasing the PPy content while BaFe as electrically insulative has a negligible effect on electrical conductivity. Less than 0.2% transmission was observed in the NIR region and a maximum SE of 88.5 dB was achieved with absorption dominant mechanism. The main reason for enhanced EMI SE of nanocomposites is dispersion state, fillers interaction with the polymer matrix, and fillers nature.

Reduced Graphene Oxide/Fe3O4/Polyaniline Ternary Composites as a Superior Microwave Absorber in the Shielding of Electromagnetic Pollution.

The present work is focused on fabrication of reduced graphene oxide/iron(II/III) oxide/polyaniline (RGO/Fe3O4/PANI) ternary composite by a hydrothermal method, its characterization, and application in the development of a high microwave absorbing shielding material. The RGO/Fe3O4/PANI composite showed dramatic enhancement of dielectric loss and magnetic loss compared to Fe3O4/PANI and RGO/Fe3O4 binary composites. This is ascribed to the embedment of more heterostructure phases. As a result, RGO/Fe3O4/PANI showed remarkably high SET (∼28 dB) through the absorption dominant mechanism. Our findings also showed maximum RL of Fe3O4/PANI, RGO/Fe3O4, and RGO/Fe3O4/PANI in the range of 2–8 GHz corresponding to −25 to −35, −40 to −46, and approximately −64 dB, respectively. This is in all probability due to the good impedance matching between permittivity/permeability and dielectric/magnetic losses.

Tuning the polymerization sequence of alkynyl-functionalized benzoxazine: application as precursor for efficient magnetic EMI shielding materials

The polymerization sequence of a benzoxazine monomer (A1) bearing alkynyl functional group is tuned by acetylacetone nickel (AN), and the resultant polybenzoxazines are used as precursors to prepare C/Ni composites with high electromagnetic interference shielding effectiveness (EMI SE). It is found that AN effectively promotes the trimerization of the alkynyl groups and forms more benzene rings in the obtained polybenzoxazines [poly(A1/AN)s], whereas polyA1 is a typical phenolic Mannich-type polybenzoxazine. Comparatively, poly(A1/AN)s possess higher cross-linking density, higher modulus at rubbery state and higher char yield at 800 °C. After carbonization, polyA1 heavily swells and deforms and the corresponding carbonaceous material cannot be used as EMI shielding material. Nevertheless, poly(A1/AN)s show good dimensional stability and the resultant magnetic carbonaceous material [C(A1/AN)s] possesses high electrical conductivity above 6 S/m and EMI SE above 25 dB. Thorough investigations reveal that appropriate amount of AN is beneficial to high graphitization degree, but excess AN lowers the graphitization degree. Therefore, the electrical conductivity decreases, while the magnetic hysteresis loss increases with the increasing of AN. Consequently, the EMI SE of C(A1/AN) increases and then decreases with the addition of AN, with C(A1/10AN) offering the highest EMI SE of 50 dB and showing an absorption-dominant mechanism.

Facile construction of 2D MXene (Ti3C2Tx) based aerogels with effective fire-resistance and electromagnetic interference shielding performance

• Preparation of non-toxic, lightweight and fire-resistant EMI shielding aerogel. • Such aerogels are fabricated by freeze-drying method. • High SSE/t value (5729 dB cm 2 g −1 ) exceeds many other reported porous materials. Rapid growing of electronics has not only caused severe electromagnetic wave pollution, but also created a risk of fire and explosion. Therefore, developing ultralight, fire-resistant, high-performance electromagnetic interference (EMI) shielding materials are imperative but also challenging. Considering the outstanding metallic conductivity and high aspect ratio, 2D Ti 3 C 2 T x has been reported to be one of the most promising candidates for exhibiting excellent EMI shielding performance. Herein, we demonstrate a facile method to fabricate cellulose nanofiber (CNF)/ammonium polyphosphate (APP)/Ti 3 C 2 T x composite aerogels via a simple freeze-drying method. The resultant CNF/APP/Ti 3 C 2 T x composite aerogels exhibited excellent fire-resistance without obvious shrinkage when placed over the flame of an alcohol burner. Besides, the 8-mm-thick composite aerogel with 60% of Ti 3 C 2 T x showed an average EMI shielding effectiveness of 55 dB (specific EMI shielding effectiveness/thickness could be ~5729 dB cm 2 g −1 ) with an absorption-dominant mechanism. This performance is owing to the relative high electrical conductivity (12 S/m) and multiple reflections from the porous structure. These characteristics make the composite aerogel a much more competitive product for a high-performance EMI shielding material.

Electromagnetic interference shielding property of polybenzoxazine/graphene/nickel composites

Composite filler of graphene/Nickel (GN) was prepared by in-situ reduction of nickel ions in basic solution of ethanol and water. Graphene layers in GN were decorated by flower-shaped nickel particles in the size of around 100 nm and homogeneous films of ternary composites were prepared from polybenzoxazine and GN. It was found that only 1 wt% of GN could increase the electrical conductivity from 1.57 × 10−12 S/cm (1 Hz) to 3.10 × 10−4 S/cm (1 Hz). As a result, the composites possessed high electromagnetic interference shielding effectiveness (EMI SE) in X-band range and showed an absorption-dominant mechanism. Addition of 3 wt% of GN could meet the requirement of commercial application (>20 dB). Moreover, the uniform dispersion of GN and strong interaction between fillers and matrix ensured greatly improved storage modulus, glass transition temperature, thermal stability and thermal conductivity.

Electroless Ag-plated sponges by tunable deposition onto cellulose-derived templates for ultra-high electromagnetic interference shielding

Environmental-friendly cellulose-derived sponges were employed as porous templates to achieve uniform Ag deposition via a facile and economical electroless plating method. SEM and BET results confirmed an Ag layer was deposited on cellulose composite sponges without damaging the porous structure. XPS and XRD analysis demonstrated substantial interactions between porous substrates and Ag particles. When utilized as electromagnetic interference (EMI) shielding materials, a 3.2 mm thick silver-plated sponge exhibited a total shielding effectiveness (SEtotal) value of as high as 120.85 dB in the frequency range of 10–1500 MHz when the plating time was 120 min. Moreover, the conductive sponges displayed absorption-dominant mechanism to alleviate secondary radiation, making them promising candidates as high EMI shielding materials.

Preparation and the electromagnetic interference shielding in the X-band of carbon foams with Ni-Zn ferrite additive

The composite of carbon foam with Ni-Zn ferrite as additive has been developed via foaming and carbonization process for electromagnetic interference shielding, using coal tar pitch as precursor and Ni-Zn ferrite as an additive. It was observed that the shielding effectiveness (SE) over the X-band frequency is enhanced along with the increase of Ni-Zn ferrite additive amount. The carbon foam with 15wt% Ni-Zn ferrite shows a SE of 42dB, which has a promising application prospect. The electromagnetic interference shielding mechanism of carbon foam with different amount of Ni-Zn ferrite additive is discussed in the work. An absorption-dominant mechanism, which is mainly associated with the magnetic property determined by the amount of Ni-Zn ferrite additive, has been revealed. It is also found that the mechanical strength of resultant carbon foams increases firstly and then decreases with the continuously increased amount of Ni-Zn ferrite additive.

Compressible Graphene-Coated Polymer Foams with Ultralow Density for Adjustable Electromagnetic Interference (EMI) Shielding.

The fabrication of low-density and compressible polymer/graphene composite (PGC) foams for adjustable electromagnetic interference (EMI) shielding remains a daunting challenge. Herein, ultralightweight and compressible PGC foams have been developed by simple solution dip-coating of graphene on commercial polyurethane (PU) sponges with highly porous network structure. The resultant PU/graphene (PUG) foams had a density as low as ∼0.027-0.030 g/cm(3) and possessed good comprehensive EMI shielding performance together with an absorption-dominant mechanism, possibly due to both conductive dissipation and multiple reflections and scattering of EM waves by the inside 3D conductive graphene network. Moreover, by taking advantage of their remarkable compressibility, the shielding performance of the PUG foams could be simply adjusted through a simple mechanical compression, showing promise for adjustable EMI shielding. We believe that the strategy for fabricating PGC foams through a simple dip-coating method could potentially promote the large-scale production of lightweight foam materials for EMI shielding.

Optical torque from enhanced scattering by multipolar plasmonic resonance

AbstractWe present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field and thereby produce scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamaterials.

Electromagnetic Interference (EMI) Shielding of Ordered Mesoporous Carbon (OMC)/Paraffin Composites

The ordered mesoporous carbon (OMC)/paraffin composites were successfully prepared by a facile physical mixing method and an EMI SE of 21-23 dB was achieved at the OMC loading of 5.69 wt.% in the X band. This indicates that the composites are very suitable for an application as effective and lightweight EMI shielding materials. The EMI shielding of the composite shows an absorption-dominant mechanism, i.e., a contribution shift from reflection to absorption is observed with the increase in OMC loading and frequency. This could be explained by the intrinsic properties (electrical conductivity, complex permittivity and potential large defects) and novel structure of the composites.

Electromagnetic shielding mechanisms using soft magnetic stainless steel fiber enabled polyester textiles

This work studied the effects of conductivity, magnetic loss, and complex permittivity when using blended textiles (SSF/PET) of polyester fibers (PET) with stainless steel fibers (SSF) on electromagnetic wave shielding mechanisms at electromagnetic wave frequencies ranging from 30MHz to 1500MHz. The 316L stainless steel fiber used in this study had 38vol% γ austenite and 62vol% α′ martensite crystalline phases, which was characterized by an x-ray diffractometer. Due to the magnetic and dielectric loss of soft metallic magnetic stainless steel fiber enabled polyester textiles, the relationship between the reflection/absorption/transmission behaviors of the electromagnetic wave and the electrical/magnetic/dielectric properties of the SSF and SSF/PET fabrics was analyzed. Our results showed that the electromagnetic interference shielding of the SSF/PET textiles show an absorption-dominant mechanism, which attributed to the dielectric loss and the magnetic loss at a lower frequency and attributed to the magnetic loss at a higher frequency, respectively.

Comparison of electromagnetic interference shielding properties between single-wall carbon nanotube and graphene sheet/polyaniline composites

Single-wall carbon nanotube/polyaniline (SWCNT/PANI) and graphene sheet/polyaniline (GS/PANI) composites were prepared by a simple alcohol-assisted dispersion and pressing process. The SWCNTs and GSs were synthesized by the dc arc-discharge method. The dc electrical conductivity and the electromagnetic interference (EMI) shielding effectiveness (SE) of these two kinds of composites were measured. The experimental results reveal that the conductivity and the EMI SE of the GS/PANI composite are better than that of the SWCNT/PANI composite, and the absorption proportion of the SWCNT/PANI composite is higher than that of the GS/PANI composite. The EMI shielding results (2–18 GHz) also show that both composites present an absorption-dominant mechanism and present a wide application prospect in the field of EMI shielding and microwave absorption.