We prepared poly(vinylidene fluoride) (PVDF)/carbon/Ni-chain composites by dispersing Ni chains, and either carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs) into a PVDF solution. The ...electrical conductivity and the electromagnetic interference (EMI) shielding properties of the PVDF/CNT/Ni-chain and the PVDF/GNP/Ni-chain composites were increased by increasing the Ni-chain filler content. The electrical conductivity of the PVDF/CNT/10 wt%Ni-chain composite was lower than the PVDF/CNT/6 wt%Ni-chain composite. We attributed this abnormality to the Ni chains having blocked the CNT connections, when there was a high Ni-chain content. Furthermore, the PVDF-based composites' EMI shielding properties were effectively tuned by controlling the films' thicknesses. The total shielding of the PVDF/CNT/6 wt%Ni-chain and the PVDF/GNP/8 wt%Ni-chain composite films increased from 23.6 to 57.3 dB and from 22.7 to 55.8 dB, as their thicknesses were increased from 0.3 mm to 0.6 mm, respectively. The synergetic relationship between the Ni chains and the carbon materials (CNT or GNP), meant that the main EMI shielding mechanisms of the PVDF/carbon/Ni-chain composites had resulted from the absorption process. Moreover, these composites possessed high thermal conductivity, which can convert microwave energy into Joule heating systems. Thus, these PVDF-based composite films can be used to make high-efficiency EMI shielding devices that can rapidly dissipate heat.
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Lightweight and flexible ternary composites with graphene (Gn), silicon carbide nanowires (SiCnw), and poly (vinylidene fluoride) (PVDF) matrix were successfully fabricated via electrostatic assembly ...and solution casting followed by hot-pressing. The synergism of two-dimensional Gn and one-dimensional SiCnw with stacking fault structure improved the formation of conductive paths and multiple interfaces. This enhanced the dielectric properties, electromagnetic interference (EMI) shielding and thermal conduction performance of the fabricated composites. For instance, by the incorporation of 9.5 wt % Gn-SiCnw, the dielectric constant and the dielectric loss of the composites were increased by 4 orders of magnitude compared with neat PVDF. A maximum EMI shielding effectiveness (SE) of 32.5 dB was achieved for the composites at 1.2 mm thickness in the frequency range 8.2–12.4 GHz. The high EMI SE of the Gn-SiCnw/PVDF can be attributed to the high electrical conductivity, dielectric constant and dielectric loss. The composites also showed a high thermal conductivity of 2.13 W. m−1. K−1, due to the formation of a thermally conductive network between Gn and SiCnw. This dual functionality of the Gn-SiCnw/PVDF composites demonstrates that they are outstanding materials with potential applications in EMI shielding and thermal management for microelectronics.
The self-assembly of Graphene and SiC nanowires provided a unique microstructure, imparting the graphene/SiC nanowires/PVDF composites with high EMI shielding and thermal conductivity at low filler content. Display omitted
As electronic devices become increasingly miniaturized, their thermal management becomes critical. Efficient heat dissipation guarantees their optimal performance and service life. Graphene ...nanoplatelets (GnPs) have excellent thermal properties that show promise for use in fabricating commercial polymer nanocomposites with high thermal conductivity. Herein, an industrially viable technique for manufacturing a new class of lightweight GnP–polymer nanocomposites with high thermal conductivity is presented. Using this method, GnP−high-density polyethylene (HDPE) nanocomposites with a microcellular structure are fabricated by melt mixing, which is followed by supercritical fluid (SCF) treatment and injection molding foaming, which adds an extra layer of design flexibility. Thus, the microstructure is tailored within the nanocomposites and this improves their thermal conductivity. Therefore, the SCF-treated HDPE 17.6 vol % GnP microcellular nanocomposites have a solid-phase thermal conductivity of 4.13 ± 0.12 W m–1 K–1. This value far exceeds that of their regular injection-molded counterparts (2.09 ± 0.03 W m–1 K–1) and those reported in the literature. This dramatic improvement results from in situ GnPs’ exfoliation and dispersion, and from an elevated level of random orientation and interconnectivity. Thus, this technique provides a novel approach to the development of microscopically tailored structures for the production of lighter and more thermally conductive heat sinks for next generations of miniaturized electronic devices.
Highlights
The successful fabrication of layered foam/film structure via the crystal melting temperature mismatch for two grades of PVDF resin in a batch foaming process.
Developing the ...heterostructure interfaces between SiC nanowires and MXene (Ti
3
C
2
T
x
) nanosheets.
Achieving efficient electromagnetic interference shielding effectiveness with ultralow reflectivity.
Lightweight, high-efficiency and low reflection electromagnetic interference (EMI) shielding polymer composites are greatly desired for addressing the challenge of ever-increasing electromagnetic pollution. Lightweight layered foam/film PVDF nanocomposites with efficient EMI shielding effectiveness and ultralow reflection power were fabricated by physical foaming. The unique layered foam/film structure was composed of PVDF/SiCnw/MXene (Ti
3
C
2
T
x
) composite foam as absorption layer and highly conductive PVDF/MWCNT/GnPs composite film as a reflection layer. The foam layer with numerous heterogeneous interfaces developed between the SiC nanowires (SiCnw) and 2D MXene nanosheets imparted superior EM wave attenuation capability. Furthermore, the microcellular structure effectively tuned the impedance matching and prolonged the wave propagating path by internal scattering and multiple reflections. Meanwhile, the highly conductive PVDF/MWCNT/GnPs composite (~ 220 S m
−1
) exhibited superior reflectivity (R) of 0.95. The tailored structure in the layered foam/film PVDF nanocomposite exhibited an EMI SE of 32.6 dB and a low reflection bandwidth of 4 GHz (R < 0.1) over the Ku-band (12.4 − 18.0 GHz) at a thickness of 1.95 mm. A peak SE
R
of 3.1 × 10
–4
dB was obtained which corresponds to only 0.0022% reflection efficiency. In consequence, this study introduces a feasible approach to develop lightweight, high-efficiency EMI shielding materials with ultralow reflection for emerging applications.
While elastic properties of nanoconfined polymer films have been recognized to show departures from bulk behavior, a careful understanding of the origins of mechanical size effects remains weak. ...Here, we report a significant mechanical stiffening of freestanding ultrathin poly(methyl methacrylate) films of varying thicknesses (6–200 nm) through atomic force microscopy deflection measurements at ambient conditions. After excluding the substrate influence, the stiffening mechanism is linked to extended chain conformations based on small-angle X-ray scattering and infrared nanoscopic characterization. We advocate that the entropic elasticity of individual chains plays a significant role in polymer mechanics in nanoscale thickness films, where the entanglement density is apparently low, with chains oriented in the plane of the film, unlike a bulk polymer. Molecular dynamics simulations further unveil the dominance of entropic contributions over enthalpic contributions to the chain stiffness that endows polymer films with higher load-bearing capacity and accounts for the stiffening at the nanoscale. The results presented herein provide a mechanistic understanding of molecular origins of the size effect, serving as a potent design strategy for accessing high-performance polymer-based devices.
In this study, we fabricated conductive poly(vinylidene fluoride) (PVDF)/carbon composites simply by dispersing multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets into a PVDF solution. ...The electrical conductivity and the electromagnetic interference (EMI) shielding of the PVDF/carbon composites were increased by increasing the conductive carbon filler amounts. Moreover, we also found that the EMI shielding properties of the PVDF/CNT/graphene composites were higher than those of PVDF/CNT and PVDF/graphene composites. The mean EMI shielding values of PVDF/5 wt %-CNT, PVDF/10 wt %-graphene, and PVDF/CNT/graphene composite films with a thickness of 0.1 mm were 22.41, 18.70, and 27.58 dB, respectively. An analysis of the shielding mechanism showed that the main contribution to the EMI shielding came from the absorption mechanism, and that the EMI shielding could be tuned by controlling the films’ thickness. The total shielding of the PVDF/CNT/graphene films increased from 21.90 to 36.46 dB as the thickness was increased from 0.06 mm to 0.25 mm. In particular, the PVDF/carbon composite films, with a thickness of 0.1 mm, achieved the highest specific shielding values of 1 310 dB cm2/g for the PVDF/5 wt %-CNT composite and 1 557 dB cm2/g for the PVDF/CNT/graphene composite, respectively. This was due to the ultrathin thickness. Our study provides the groundwork for an effective way to design flexible, ultrathin conductive polymer composite film for application in miniaturized electronic devices.
In recent decades, problems with electromagnetic interference (EMI) radiation problems have arisen, that can seriously reduce the performance of precision devices nearby and threaten human health. In ...consequence, it is important to seek high efficiency materials to suppress EMI pollution. Generally, high magnetic permeability or electrical conductivity is essential for efficient EMI shielding. Conventionally, various forms of metal construction (sheet/films, coatings,
etc.
) are used for EMI shielding. However, metallic shielding has drawbacks that include high density, lack of corrosion resistance and expensive processing, which restrict its use in the modern electronic world. By contrast, conductive polymer composites (CPCs), formed from insulative polymers and conductive fillers, have attracted more and more interest from both industry and academia. CPCs have properties that offer great potential for application in efficient EMI shielding. These include low density, high flexibility, good chemical stability and easy processing and forming. From a theoretical viewpoint, it is generally accepted that the shielding of EM waves is due to the three basic mechanisms of reflection, absorption and multiple internal reflections. However, it must be recognized that the SE of CPCs has a close relation to the reflection mechanism, which can cause secondary EMI pollution. Therefore, materials with charge carriers or magnetic/electric dipoles as well as cellular structure should be the focus for the development of EMI shielding materials with strong absorption properties. On that basis, the main aim of this paper is to review the current position in research of the design of inorganic based foams (metal, carbon or MXene) and polymer composite foams as EMI shielding materials. On the one hand, these composite foams have the merit of being lightweight, and on the other hand, the special porous structure can effectively harvest microwaves by prolonging the travel path. As a result, absorption dominates EMI shielding, which satisfies current requirements of EMI shielding applications. This review also points out the future challenges and gives guidelines for finding solutions for the next generation of shielding applications using composite foams.
In recent decades, problems with electromagnetic interference (EMI) radiation problems have arisen, that can seriously reduce the performance of precision devices nearby and threaten human health.
Recently, laser welding technologies have been widely utilized to weld different automobile panels. In this research, the laser beam welding (LBW) process of interstitial free (IF) steel sheets used ...in the manufacturing of the car body was investigated on the basis of mathematical models. The quality indexes of LBW joints were estimated from Erichsen Cupping Test results including strength and Erichsen Cupping Index. Furthermore, three process parameters, namely laser power (
P
), welding speed (
S
), and focal position (
F
) were considered as the factors influencing the quality indexes. A 2.2-kW CO
2
-laser beam was utilized to weld 1.2- and 0.8-mm-thick IF steel sheets. The modeling is done using experimental data which were gathered using design of experiments approach based on central composite face centered design matrix. The final regression models can be used to predict the quality indexes of laser beam-welded IF steel sheets joints at 95% confidence level. Optical metallography was utilized to characterize the weld profile and microstructures. In the second phase of this research, multi-objective genetic algorithm with the fitness function based on regression models was employed as an optimization procedure; as a result, the best quality indexes were obtained. Optimization results showed high compatibility with the actual experimental data.
Polymer crystallization on CNT surfaces has been considered to be a critical reason for the relatively high percolation thresholds obtained in melt-blended polymer/CNT nanocomposites (e.g., ...generally > 1 wt% in most polyolefin/CNT systems). In this work, the crystal-nucleating capability of CNTs in polypropylene (PP) was controlled through addition of a sorbitol-based external nucleating agent (NA) and via controlling the cooling rate. Despite the competition between CNT and NA for crystal nucleation, little increase in conductivity was obtained as compared to PP/CNT with fast cooling (~150 °C/min). However, with a slow cooling process (~1.5 °C/min), large PP crystallites were induced with only a small number of nuclei. Therefore, the majority of the CNT particles were prevented from participating in the nucleation of PP crystals so that they could be concentrated to form conductive networks through an enhanced volume exclusion effect. This significantly increased the conductivity of the PP/CNT nanocomposites, and the percolation threshold was greatly reduced from 0.75 wt% to 0.36 wt%. The work highlights the crucial influence of controlling CNT nucleation capability and the polymer crystallite size on the conductivity using slow cooling in addition to annealing treatment.
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Electrochemical Microactuators
In article number 2304517, Mahdi Hamidinejad, Michael De Volder, and co‐workers introduce a new type of ultralow‐power electrochemical microactuator. These ...microsctructures are made out of lithographically defined 3D carbon nanotube architectures that are loaded with active materials that can alloy with lithium. Upon electrochemical lithiation and delithiation of that material, the microstructures are actuated reversibly.
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