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)

Conductive polymer composites with segregated structures

Light-weight and high-performance electromagnetic interference (EMI)-shielding epoxy nanocomposites are prepared by an infiltration method using a 3D carbon nanotube (CNT) sponge as the 3D reinforcement and conducting framework. The preformed, highly porous, and electrically conducting framework acts as a highway for electron transport and can resist a high external loading to protect the epoxy nanocomposite. Consequently, a remarkable conductivity of 148 S m−1 and an outstanding EMI shielding effectiveness of around 33 dB in the X-band are achieved for the epoxy nanocomposite with 0.66 wt% of CNT sponge, which is higher than that achieved for epoxy nanocomposites with 20 wt% of conventional CNTs. More importantly, the CNT sponge provides a dual advantage over conventional CNTs in its prominent reinforcement and toughening of the epoxy composite. Only 0.66 wt% of CNT sponge significantly increases the flexural and tensile strengths by 102% and 64%, respectively, as compared to those of neat epoxy. Moreover, the nanocomposite shows a 250% increase in tensile toughness and a 97% increase in elongation at break. These results indicate that CNT sponge is an ideal functional component for mechanically strong and high-performance EMI-shielding nanocomposites.

High-Performance Epoxy Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding

Carbon materials for structural self-sensing, electromagnetic shielding and thermal interfacing

Functionalization of carbon nanomaterials for advanced polymer nanocomposites: A comparison study between CNT and graphene

The electromagnetic interference (EMI) shielding mechanism of carbon nanotube (CNT)/polymer nanocomposites synthesized through a unique processing technique has been studied. As CNT/polymer nanocomposites evolve towards device applications, homogenous dispersion of CNTs has become a main objective to realize their full potential. In this work, dispersion of multi-walled carbon nanotubes (MWCNTs) in polystyrene (PS) powder via dry state tumble mixing has been carried out. This involves the coating of the PS particles with the MWCNTs. Pellets were prepared by hot compression of resulted mixture. Conductivity behavior has shown that an extremely small mass fraction of 0.05 wt % MWCNTs in PS is good enough for percolation threshold. A detailed study of EMI shielding behavior of these composites is reported in addition to physical phenomena involved. The shielding effectiveness achieved is higher compared to solution mixing technique used by others. Decrease in hardness with increase in MWCNT content is little. Scanning electron microscope studies of these nanocomposites revealed a web/mesh like structure consisting of MWCNTs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40201.

Electrical and EMI shielding characterization of multiwalled carbon nanotube/polystyrene composites

Dispersion of graphite within the acrylonitrile butadiene styrene matrix demonstrates enhanced electromagnetic interference shielding of composites through the use of tumble mixing technique. A shielding effectiveness of 60 dB with 15 wt % of graphite has been achieved. D shore hardness data revealed a little decrease in hardness of composites with rise in graphite content. DC conductivity measurements revealed a fairly low percolation threshold at 3 wt % of graphite. The conductivity exhibited by 15 wt % composite is 1.66 × 10−1 S/cm. These composites are fit for use as an effective and convenient EMI shielding material because of easy processing, better hardness, light weight, and, reasonable shielding efficiency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Electromagnetic Interference Shielding of Graphite/Acrylonitrile Butadiene Styrene Composites

Insulator conductor transition in low-density polyethylene–graphite composites

This paper reports on the p to n transition in Pb doped Se–In chalcogenide glasses. Measurements of thermoelectric power in the temperature range 300 K⩽T⩽315 K, dc conductivity in the temperature range 100⩽T⩽300 K, and optical band gap (Egopt) have been carried out for Se75In25−xPbx (x=0,5,10,15) samples. The p-n transition occurs with very low addition of Pb impurity (5 at. %). The conductivity and pre-exponential factor also change by five to six orders of magnitude with Pb doping. Results are explained on the basis of the formation of ionic Pb–Se bonds, instead of covalent bonds. Formation of ionic bonds disturbs the equilibrium between the charged defect states of Se–In glass and unpins the Fermi level and thus leads to n-type conduction in these glasses.

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n-Type conduction in Pb doped Se-In chalcogenide glasses

IntroductionDisorderedconductor–insulatorcompositesexhibitavarietyof phenomena, some of which have important commercialapplications. Among large number of composite materials,conductive polymer composites have been extensively usedin resistors, self regulating heaters, over current and overtemperature circuit protection devices, antistatic materials,and materials for electromagnetic interference shielding. Inorder to analyze the conducting behavior in such systems onmicroscopic scale, several models have been proposed, suchaspercolationtheory[1],effectivemediatheoryasprojectedby Bruggeman [2], aggregate structure model which over-come the disadvantage of effective media theory [3], andMcLachlan’s general effective medial (GEM) theory whichcombines most of the features of both percolation andeffective mediatheory[4].GEM equationis aninterpolationbetween Bruggeman’s symmetric and asymmetric theories.The format of equation is in the same mathematical form asof the percolation equation of conductivity when the ratio ofconductivities of the two components is inﬁnitely large.Whileintroducingthisequationithasbeen supposedthatthebinary system is microscopically homogeneous, the particlesize distributions are inﬁnitely wide and the particles are incontact with each other with no voids. This equation isapplicable to all volume fractions and not only near theinsulator–conductor transition as in percolation theory.In the past few decades, some works on effective mediatheory on polymer composites ﬁlled with carbon blackparticles have been reported [3, 5], but the use of graphite asﬁller is almost unavailable in literature. The experimentalstudies in which the critical behavior of polymer compositeshave been investigated using effective media theory are sofar concerned with system of sphere-like conducting parti-cles embedded in an insulating matrix. A reasonableagreement between the experimental results and theoreti-callypredictedcriticalbehaviorofconductivitywasfound[5].This work presents the study of decisive behavior ofpercolation process using general effective media theory ina composite in which the conducting particles localized inan insulating matrix are better described as ﬂakes, thanspheres. Previous experimental studies reported by thisgroup for graphite/polymer composites are concerned withthe qualitative features of conductivity [6] and the theo-retical studies are conﬁned only to the percolation theory[7]. No attempt has been made to explain the conductivitybehavior using GEM theory. In the present work, con-ducting behavior of a series of graphite/HDPE compositeshas been studied experimentally. A comparative analysis ofapplicability of GEM equation for expressing of conduc-tivity behavior of HDPE composites ﬁlled with differentﬁllers has been made. The effect of processing methodsbesides shape and size of ﬁller particles has been discussed.ExperimentalCommercial grade of high density polyethylene used in thiswork was procured from Reliance industry, India. Flakeshaped graphite powder [7] supplied by Graphite India wasselected as ﬁller. The particle size was ranging from 10 to20 lm with a resistivity of 7.5 9 10

V. K. Sachdev

Papers

Electrical and EMI shielding characterization of multiwalled carbon nanotube/polystyrene composites

Electromagnetic Interference Shielding of Graphite/Acrylonitrile Butadiene Styrene Composites

Insulator conductor transition in low-density polyethylene–graphite composites

n-Type conduction in Pb doped Se-In chalcogenide glasses

Electrical conduction of graphite filled high density polyethylene composites; experiment and theory