Li-Chuan Jia

Electrically conductive and electromagnetic interference shielding of polyethylene composites with devisable carbon nanotube networks

This paper reports a comparative study of the electrical and electromagnetic interference (EMI) shielding performance of three carbon nanotube/polyethylene (CNT/PE) composites with different conductive networks, i.e., segregated structure (s-CNT/PE), partially segregated structure (p-CNT/PE) and randomly distributed structure (r-CNT/PE). The s-CNT/PE composite exhibits superior electrical conductivity up to 2 orders of magnitude over that of p-CNT/PE and r-CNT/PE composites, at the same CNT loading. Only 5 wt% CNT addition in the s-CNT/PE composite realizes an excellent EMI shielding effectiveness (SE) as high as 46.4 dB, which is 20% and 46% higher than that for p-CNT/PE and r-CNT/PE composites, respectively. The selectively distributed CNTs at the interfaces between PE polyhedrons would certainly increase the effective CNT concentrations that form conducting pathways and thus increase the electrical conductivity and EMI SE in the s-CNT/PE composites. Such special structure also provides numerous interfaces that absorb the electromagnetic waves, resulting in an absorption-dominated shielding mechanism. Our work suggests that designing conductive networks in polymer composites is a promising approach to develop high-performance EMI shielding materials.

A strong and tough polymer–carbon nanotube film for flexible and efficient electromagnetic interference shielding

Carbon nanotube (CNT) films exhibit potential use in broad areas including energy-storage, thermal management, and electromagnetic interference (EMI) shielding; however, their inefficient, expensive, and energy-consuming fabrication processes reported so far and mechanical brittleness are a major deficiency. Herein, a strong and tough carbon nanotube (CNT) film with the inclusion of natural rubber (NR) was fabricated for flexible and efficient EMI shielding by a facile, efficient, and energy-saving method. Compared to the pure CNT film, the incorporation of 50 wt% NR leads to a tremendous mechanical improvement of the CNT-NR films, e.g., a 3.1 and 486 times increase in tensile strength and toughness. The origin of the reinforcing and toughening effect of the CNT films by the addition of a rubber material mainly arises from enhanced stress transfer and the uniformly dispersed stress. The CNT-NR film displays excellent EMI shielding performance albeit at tiny thickness owing to the extremely high aspect ratio and electrical conductivity of CNTs. The critical thickness required to satisfy commercial EMI shielding applications (shielding effectiveness (SE) of 20 dB) is only 50 μm, and a very high EMI SE of 44.7 dB is achieved as the film thickness reaches 250 μm. Meanwhile, the CNT-NR film exhibits highly reliable EMI SE even after bending 5000 times at a radius of 2.0 mm. These intriguing properties of CNT-NR films, together with their advantages of environmentally friendly and facile large-scale fabrication, open up the possibility of designing highly thin and flexible films for promising electromagnetic protection, especially in aerospace, aviation, and next-generation flexible electronics.

Highly Efficient and Reliable Transparent Electromagnetic Interference Shielding Film

Electromagnetic protection in optoelectronic instruments such as optical windows and electronic displays is challenging because of the essential requirements of a high optical transmittance and an electromagnetic interference (EMI) shielding effectiveness (SE). Herein, we demonstrate the creation of an efficient transparent EMI shielding film that is composed of calcium alginate (CA), silver nanowires (AgNWs), and polyurethane (PU), via a facile and low-cost Mayer-rod coating method. The CA/AgNW/PU film with a high optical transmittance of 92% achieves an EMI SE of 20.7 dB, which meets the requirements for commercial shielding applications. A superior EMI SE of 31.3 dB could be achieved, whereas the transparent film still maintains a transmittance of 81%. The integrated efficient EMI SE and high transmittance are superior to those of most previously reported transparent EMI shielding materials. Moreover, our transparent films exhibit a highly reliable shielding ability in a complex service environment, with 98 and 96% EMI SE retentions even after 30 min of ultrasound treatment and 5000 bending cycles (1.5 mm radius), respectively. The comprehensive performance that is associated with the facile fabrication strategy imparts the CA/AgNW/PU film with great potential as an optimized EMI shielding material in emerging optoelectronic devices, such as flexible solar cells, displays, and touch panels.

Percolation and resistivity-temperature behaviours of carbon nanotube-carbon black hybrid loaded ultrahigh molecular weight polyethylene composites with segregated structures

An ultrahigh molecular weight polyethylene (UHMWPE) composite containing carbon nanotube–carbon black (CNT–CB) hybrid was fabricated via a facile method, i.e., mechanical mixing plus hot compaction in order to obtain low-cost conductive polymer composites with balanced electrical properties. Optical microscope and scanning electron microscope observations indicate the formation of a typical segregated structure in the CNT–CB/UHMWPE composite, with the CNT–CB hybrid selectively located at the interfaces of UHMWPE granules. Compared to the single CNT loaded UHMWPE composite, the CNT–CB/UHMWPE segregated composite with a quarter replacement of CNT with CB shows only 8% decline in electrical conductivity, with the same filler content of 4 wt%, realizing a significant reduction in the material cost. More interestingly, the CNT–CB/UHMWPE composite presents 273% higher positive temperature resistivity intensity than that of CNT/UHMWPE composites, exhibiting strong sensitivity to ambient temperature. Our work demonstrates a novel strategy to fabricate low-cost and high-performance conductive polymer composites by the combination of hybrid fillers and a segregated structure.

Synergistic effect of graphene nanosheets and carbonyl iron–nickel alloy hybrid filler on electromagnetic interference shielding and thermal conductivity of cyanate ester composites

In this study, a promising cyanate ester nanocomposite with an excellent electromagnetic interference shielding effectiveness (EMI SE) and high thermal conductivity was fabricated by compounding graphene nanosheets (GNSs) and magnetic carbonyl iron–nickel alloy powder (CINAP) via a solution blending method and subsequent hot-pressing. The obtained 5 wt% GNSs/cyanate ester (CE) nanocomposite possesses the outstanding EMI SE of 38 dB and this property was synergistically enhanced to attain the value of 55 dB with the presence of 20 wt% CINAP. In addition, the GNSs/CINAP/CE nanocomposite with 5 wt% GNSs and 15 wt% CINAP exhibits high thermal conductivity (K = 4.13 W m−1 K−1). This synergistic enhancement is significantly affected by the formation of the efficient 3D electric and thermally conductive pathways as well as the dispersion of the incorporated fillers. This highly thermally conducting CE nanocomposite with the efficient EMI shielding properties has a potential to be used in advanced electronic packaging.

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.

Efficient electromagnetic interference shielding of lightweight carbon nanotube/polyethylene composites via compression molding plus salt-leaching

Carbon nanotube/high density polyethylene (CNT/HDPE) foam composites with high electrical conductivity and electromagnetic interference (EMI) shielding performance were developed by means of compression molding plus salt-leaching. The uniform porous structure and interconnected CNT networks throughout the cell backbones endowed the as-prepared foam composites with a significantly lower electrical percolation threshold (0.22 vol%) than that of the solid composites (0.84 vol%). Owing to the multiple reflections and scattering between the cell–matrix interfaces, the foam composites presented a superior specific EMI shielding effectiveness (EMI SE) of 104.3 dB cm3 g−1, 2.2 times higher than that of their solid counterpart. Besides this, the pore sizes of the CNT/HDPE foam composites could be easily tuned by controlling the particle size of the porogen. Also, the electrical conductivity and specific EMI SE increased with an increase in the cell diameter, which was attributed to the formation of a more perfect conductive network in the cell backbones. Our approach provides a novel idea for fabricating new lightweight EMI shielding materials, especially for aircraft and spacecraft applications.

Octadecylamine-Grafted Graphene Oxide Helps the Dispersion of Carbon Nanotubes in Ethylene Vinyl Acetate

In this paper, the dispersion of carbon nanotube (CNT) in ethylene vinyl acetate (EVA) is demonstrated to be significantly improved by the addition of octadecylamine (ODA)-grafted graphene oxide (GO) (GO–ODA). Compared to the CNT/EVA composite, the resultant GO–ODA/CNT/EVA (G–CNT/EVA) composite shows simultaneous increases in tensile strength, Young’s modulus and elongation at break. Notably, the elongation at break of the G–CNT/EVA composite still maintains a relatively high value of 1268% at 2.0 wt % CNT content, which is more than 1.6 times higher than that of CNT/EVA composite (783%). This should be attributed to the homogeneous dispersion of CNT as well as the strong interfacial interaction between CNT and EVA originating from the solubilization effect of GO–ODA. Additionally, the G–CNT/EVA composites exhibit superior electrical conductivity at low CNT contents but inferior value at high CNT contents, compared to that for the CNT/EVA composite, which depends on the balance of CNT dispersion and the preservation of insulating GO–ODA. Our strategy provides a new pathway to prepare high performance polymer composites with well-dispersed CNT.

Integrated strength and toughness in graphene/calcium alginate films for highly efficient electromagnetic interference shielding

Graphene films are considered promising electromagnetic interference (EMI) shielding materials in view of high electrical conductivity, light weight, and flexibility. Nevertheless, pristine graphene films exhibit only modest mechanical performance because of the weak interfaces between graphene nanosheets. We have developed an advanced graphene film that integrates excellent EMI shielding performance with improved mechanical performance, by intercalating calcium alginate (CA) molecules into reduced graphene oxide (rGO) nanosheets. The rGO/CA film exhibits an EMI shielding effectiveness (EMI SE) of 25.7 dB at only 12 μm thickness, and the corresponding specific EMI SE is 2142 dB mm−1, which is far superior to previously reported EMI shielding materials. Importantly, the rGO/CA film achieves an excellent tensile strength of 118.0 MPa and a toughness of 4.6 MJ m−3, which is 102% and 130% higher than those of the rGO film. Such significant enhancement is attributed to the synergistic interfacial interactions of hydrogen bonding between CA and rGO nanosheets and ionic bonding between calcium ions and rGO nanosheets. Moreover, the rGO/CA film shows a high EMI shielding reliability (96% EMI SE retention even after 5000 folding cycles). Its features make the rGO/CA film highly attractive for EMI shielding applications, especially in aircraft, aerospace, and next-generation flexible electronics.

Layer-Structured Design and Fabrication of Cyanate Ester Nanocomposites for Excellent Electromagnetic Shielding with Absorption-Dominated Characteristic

In this work, we propose novel layer-structured polymer composites (PCs) for manipulating the electromagnetic (EM) wave transport, which holds unique electromagnetic interference (EMI) shielding features. The as-prepared PCs with a multilayered structure exhibits significant improvement in overall EMI shielding effectiveness (EMI SE) by adjusting the contents and distribution of electrical and magnetic loss fillers. The layer-structured PCs with low nanofiller content (5 wt % graphene nanosheets (GNSs) and 15 wt % Fe3O4) and a thickness of only 2 mm exhibited ultrahigh electrical conductivity and excellent EMI SE, reaching up to 2000 S/m and 45.7 dB in the X-band, respectively. The increased EMI SE of the layer-structured PCs was mainly based on the improved absorption rather than the reflection of electromagnetic waves, which was attributed to the “absorb-reflect-reabsorb” process for the incident electromagnetic waves. This work may provide a simple and effective approach to achieve new EMI shielding materials, especially for absorption-dominated EMI shielding.