Electrical Conductive Fillers Research Articles

Investigation on piezoresistivity of self-sensing cementitious composites containing nano carbon fillers under water content variations

Self-sensing cementitious composites containing nano carbon fillers have extensive application prospects in structural health monitoring (SHM) due to their excellent intrinsic piezoresistivity, good mechanical performances, high compatibility and durability. However, the piezoresistivity is prone to be affected by environmental factors, such as water content. Therefore, it is urgent to study the influence of water content on piezoresistivity to avoid unwanted effect. In the present study, piezoresistivity of self-sensing cementitious composites containing nano carbon fillers under cyclic compression with different water contents is investigated. Moreover, mechanisms are also explored comprehensively. The results indicate that the sensitivity, repeatability and stability of the piezoresistivity deteriorate with decreasing of water content. The maximum FCR and stress/strain sensitivity are decreased from 14.3 % to 4.5 % and 0.72 %·MPa−1/124–0.23 %·MPa−1/39, respectively, when water content decreases from 3.53 % to nearly 0 %. Variation of electrical conductivity pathways and networks caused by enclosed water film on surface of electrical conductive fillers take responsible for the changeable of piezoresistivity with different water content. The outcomes offered validity of self-sensing cementitious composites implementation in SHM withstand variation of water content.

Construction of 3D Conductive Network in Liquid Gallium with Enhanced Thermal and Electrical Performance

AbstractThis paper reports the generation of 3D thermal and electrical conductive graphene network in gallium‐based liquid metal (LM) via a simple one‐step ball‐milling approach. In this work, 2D graphene nanoplates and their derivatives were employed to construct 3D thermal and electrical conductive filler networks. It is demonstrated that the obtained composite exhibits the highest 3D thermal conductivity (44.6 W m−1 K−1) among the other gallium‐based LM composites with 2D inorganic nanofillers and distinguished electrical conductivity (8.3 S µm−1) among gallium‐based LM composites at present. The enhanced thermal conductivity and wettability of gallium‐based composite lead to its beneficial usage as thermal interface materials with exquisite texture for LED chip heat dissipation. The electrochemical and magnetic experiments confirm that these LM‐based composites can also be controlled under external electrical or magnetic field, which potentially can help extend their application in external field‐driven systems. The findings of this work offer new insight in designing LM‐based composites with enhanced thermal, electrical, and magnetic properties for a wide range of applications, including thermal management systems, 3D printing, flexible conductors, soft robotic systems, and wearable energy technologies.

Polyurethane-Carbon Nanotubes Composite Dual Band Antenna for Wearable Applications.

The design of a unipole and a dual band F-shaped antenna was conducted to find the best parameters of prepared antenna. Antenna radiator part is fully made of polymer and nonmetal base composite. Thermoplastic polyurethane (PU) was chosen as a matrix and multi-wall carbon nanotubes (MWCNT) as an electrical conductive filler, which creates conductive network. The use of the composite for the antenna has the advantage in simple preparation through dip coating technique. Minor disadvantage is the usage of solvent for composite preparation. Composite structure was used for radiator part of antenna. The antenna operates in 2.45 and 5.18 GHz frequency bands. DC conductivity of our PU/MWCNT composite is about 160 S/m. With this material, a unipole and a dual band F antenna were realized on 2 mm thick polypropylene substrate. Both antenna designs were also simulated using finite integration technique in the frequency domain (FI-FD). Measurements and full wave simulations of S11 of the antenna showed good agreement between measurements and simulations. Except for S11, the gain and radiation pattern of the antennas were measured and simulated. Maximum gain of the designed unipole antenna is around −10.0 and −5.5 dBi for 2.45 and 5.18 GHz frequency bands, respectively. The manufactured antennas are intended for application in wearable electronics, which can be used to monitor various activities such as walking, sleeping, heart rate or food consumption.

Electrical and thermal stimuli responsive thermoplastic shape memory polymer composites containing rGO, Fe3O4 and rGO–Fe3O4 fillers

This work addresses a facile and broadly applicable method of fabricating a new thermoplastic shape memory polymer (SMP) composite by blending three biopolymers such as polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene glycol. Reduced Graphene (rGO) is used as electrical conductive fillers. Iron Oxide (Fe3O4) and rGO-Fe3O4 combination provides thermo-electric stimulus. Under the thermal stimulus, shape recovery rate of the SMP with hybrid fillers was faster, having quick response time (28 s) compared to electrical stimulus response time (75 s). The conductivity of the SMP matrices increased by 7, 10 and 15 orders of magnitude by incorporating Fe3O4, rGO and rGO- Fe3O4 fillers, respectively. Moreover, the proposed shape memory polymer containing rGO-Fe3O4 filler exhibits a higher Young’s modulus (> 80%) compared to neat polymer (1.75 GPa at room temperature and 0.6 GPa at glass transition temperature, Tg). A maximum stress of 2.5 MPa and 4% recoverable strain was achieved in the SMP with 10 and 15 wt% of hybrid fillers and interestingly no stored strain evolves, upon cooling below Tg. The developed SMP may be applied in morphing wing and other smart actuator applications.

Silver Nanowires Inks for Flexible Circuit on Photographic Paper Substrate.

Silver nanowires (AgNWs) have inspired many research interests due to their better properties in optical, electric, and flexible applications. One such exploitable use is as the electrical conductive fillers for print electronics. In this paper, AgNWs with mean a diameter of 80 nm and mean length of 13.49 μm were synthesized using the polyol solvothermal method. A sonication-induced scission process was used to obtain AgNWs with a length range of 7.64–11.21 μm. Further AgNWs inks were prepared with the as-synthesized AgNWs as conductive fillers in anhydrous ethanol. The conductive inks were coated on resin coated photographic paper substrate using the knife coating process and dried at room temperature. The effects of the number of layers of AgNWs coating, the concentration of AgNWs, and the length of AgNWs on the microstructure and electrical properties of samples were investigated by scanning electron microscopy and using the four-point probe method. The results show that the conductivity of the AgNWs coating increases with the increase in the number of layers in the AgNWs coating, concentration and length of the AgNWs.

Development of thermoplastic films for ultrasonic manufacturing of printed circuit boards

AbstractConventional production processes of PCB involve a high amount of complex production steps and the use of hazardous chemicals. Furthermore, a great effort is required for their recycling. Ultrasonic hot embossing of coextruded films, filled with electrical conductive fillers, could be an economic and ecological alternative for the production of PCB. This study focuses on the identification of suitable filler–matrix combinations for the isotropic and anisotropic conductive film layers. Hence, monolayer films with different fillers and filler contents are extruded. Conductivities of 8.31 and 12 S/m were measured in cross and machine direction, respectively, for a polypropylene‐film with 10 wt.‐% of CNT. This is two magnitudes below the required 535 S/m. With 70 mS/m, the conductivity in thickness direction is 115–170 times lower. This is caused by process‐related surface layers with low filler content. For steel fibers, no electrical conductivity can be measured.

Ultralight graphene micro-popcorns for multifunctional composite applications

Graphene has been widely applied in polymer nanocomposites due to its charming physical and chemical properties. However, the performance of graphene/polymer composite is hampered by the strong stacking tendency of graphene sheets. Here we introduce graphene micropopcorns (GMPs) with a hollow structure and a low stacking degree as an efficient additive for multifunctional composites. GMPs are massively fabricated via a facile thermal treatment of spray-dried graphene oxide (GO) powder. GMPs feature a low tap density (6–8 mg cm−3), a high specific surface area (947 m2 g−1) and a good solvent absorption capability (62 g g−1). This micro form of graphene can act as electrical conductive fillers with a low percolation threshold of 0.18 vol% and microcapsules of phase change materials with a 358% enhancement in thermal conductivity. Besides, the microwave absorption (MA) performance of GMPs/paraffin composites outperforms most graphene-based materials ever reported but with a record-low filler content (2.5 wt%). The large-scale producible GMPs enable an efficient method to utilize graphene to grant conventional materials with better performances and new functions.

Thermal conductivity and dielectric properties of polypropylene‐based hybrid compounds containing multiwalled carbon nanotubes

ABSTRACTIn this article, we explore the possibility to develop composites with improved thermal conductivity and electrically insulating properties. The strategy adopted is to combine a thermal and electrical conductive filler (multiwalled carbon nanotubes) with secondary dielectric (but thermally conductive) fillers. To this end, particles with different compositions, sizes, and shape were used as secondary fillers and the composites, prepared by melt compounding, are characterized in terms of thermal and dielectric properties. Results show that, in ternary formulations, an increase of thermal conductivity is always verified for all kind of secondary particles. Analogously, increments in electrical conductivity are observed for ternary compounds containing larger size secondary fillers, while a significant reduction is achieved with the addition of smaller ones. This behavior is explained in terms of mutual distribution of the fillers and is consistent with direct (scanning electron microscopy) and indirect (rheological) observations. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46470.

Carbon Based Polymer Nanocomposites for Strain Sensor Applications

Strain sensors based on the resistance change upon exposing to mechanical deformation have been drawn great interests owing to their wide applications including health monitoring, movement detection and structural health monitoring. Recently, conductive polymer composites (CPCs) based strain sensors have attracted attentions due to their quick response in the form of electrical resistance variation when subjected to tensile strain. In this work, two dimensional graphene was used as electrical conductive filler to fabricate thermoplastic polyurethane based strain sensor. Compared with other carbon based electrical conductive fillers, such as one dimensional carbon nanotube and zero dimensional carbon black, graphene possesses superior mechanical flexibility, high restorability and carrier mobility, which enable its application in highly sensitive strain sensors with good reproducibility. The effects of filler loading, strain amplitude and strain rate on the strain sensing behaviors were studied systematically. Wide range of strain sensitivity (gauge factor ranging from 0.78 for TPU with 0.6 wt% graphene at the strain rate of 0.1 min-1 to 17.7 for TPU with 0.2 wt% graphene at the strain rate of 0.3 min-1) and good sensing stability for different strain patterns were obtained. The CPCs also demonstrated good recoverability and reproducibility after stabilization by cyclic loading. This study provides a guideline for the fabrication of graphene based polymer strain sensors.

Low percolation threshold and balanced electrical and mechanical performances in polypropylene/carbon black composites with a continuous segregated structure

Abstract A novel continuous segregated structure was constructed in polypropylene (PP)/carbon black (CB) composites, to improve the electrical conductive performance and achieve a balance of the electrical conductivity and mechanical properties. Compared with traditional segregated structures reported in literature, PP matrix maintained a continuous structure instead of being separated completely by the electrical conductive fillers and CB particles formed a thorough conductive network in the continuous segregated PP/CB composites. A percolation threshold as low as 0.37 vol%, which is significantly lower than the percolation threshold of melt compounded PP/CB composites (2.75 vol%) and PP/polystyrene (PS)/CB composites (3.23 vol%) with a double percolation structure, was obtained because of the formation of the two-dimensional conductive network of CB particles. The mechanical performance tests showed that the tensile modulus, strength and elongation of break could be maintained well at CB contents around the percolation threshold. That is, with this novel continuous segregated structure, a balance of strength, toughness and electrical conductivity property can be achieved in conductive polymer composites.

Effect of wet jet milling of carbon nanotube on electrical properties of polymer nanocomposites

Wet-type jet milling (WJM) was used as a pre-treatment procedure for carbon nanotube (CNT) which was utilized as electrical conductive filler for polymer nanocomposites. Nanocomposites were prepared by dispersing WJM treated CNT (WJM-CNT) or as-received CNT (AR-CNT) in isotactic polypropylene matrix, and the effect of WJM pre-treatment on nanocomposite properties was investigated. Dispersion structure of CNT was observed by SEM and electrical property was studied by impedance spectroscopy. DC conductivities (σDC) showed different CNT concentration dependences, which were characterized by the percolation critical exponents. At 0.5 wt% of CNT, σDC increased two-fold by using WJM-CNT. Analysis of imaginary part of impedance spectra and complex dielectric permittivity suggested the WJM-CNT nanocomposites had much complicated local structure as compared to the AR-CNT counterparts. These electrical properties were discussed in relation to the dispersion structure of CNT.

Design and study of an electrical liquid heater using conductive polymer composite tubes

This study focuses on both the design and testing of an electrical heating device using current passage tubes made of Conductive Polymer Composites (CPC). To obtain such materials, an insulating polymer matrix is combined with electrical conductive fillers (carbon black, carbon fibres or metal particles). Power dissipation is observed when an electrical current is passed through the charged polymer matrix. To optimise heater design, two different axisymmetric, T(r,z) finite element models were developed with COMSOL®. The first model represents the electro-thermal behaviour of a current passage tube with internal water flow only. The second one takes into account water circulation both inside and outside the heating tube.A prototype was developed based on four immersed CPC tubes supplied electrically and hydraulically in parallel in a PVC casing. The experimental sequences performed on this pilot coupled with a hydraulic circuit made it possible to validate the two models. Analysis of the experimental recordings indicated that thermoelectric efficiency was higher than 90%. The thermal behaviour of such heaters was well defined on the basis of the information obtained from these tests and on the numerical simulations.

Using of carbon nanotubes and nano carbon black for electrical conductivity adjustment of pressure-sensitive adhesives

Electrical conductive pressure-sensitive adhesives (PSAs) are not commercially available on the market. The development of these PSAs requires special suitable self-adhesive polymers and their modification through adding of electrical conductive fillers. From the evaluated PSAs the best performances were achieved using acrylic PSAs. Common fillers for electrical conductivity are carbon nano-fillers, metallic powders like copper, aluminum, nickel, silver or gold. Acrylic PSA containing electrical conductivity fillers are applied for the manufacturing of diverse technical self-adhesive products, such as broadest line of electrically conductive sensitive double-sided, one-sided and carrier-free tapes. After addition of electrical conductive fillers the main typical properties for pressure-sensitive adhesives like tack and peel adhesion are deteriorated. In the last time the research and development on the area of nano carbon black or nanotubes as electrical conductive fillers is observed.

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.

DC and AC conductivity in epoxy resin/multiwall carbon nanotubes percolative system

This study attempts to investigate how the inclusion of Multiwalled Carbon-NanoTubes (MWCNT) influences the DC and AC conductivity response of standard high performance epoxy systems. Towards this direction, the highly electrical conductive fillers were homogenously dispersed at various weight contents (in the range of 0.1% up to 1.0%) using a well established shear mixing protocol. The DC and AC conductivity of the prepared nanocomposites was measured. AC conductivity was examined in the frequency range from 101 to 106 HZ at ambient temperature. An enhancement of conductivity, in accordance to percolation theory, was evidenced increasing the weight content of the conductive nano-filler. The AC conductivity was found to be frequency dependent beyond a critical frequency that increased with the nano-filler content. It is proposed that the critical frequency follows also a percolation type law with the weight fraction of the nanotubes. A deeper analysis of all aforementioned observations highlights the multiparametric reliance of the macroscopic electrical response on the properties of the nanotubes, their electrical network topology, and their interactions with the surrounding polymer and CNTs. POLYM. COMPOS., 31:1874–1880, 2010. © 2010 Society of Plastics Engineers.

Pseudoreinforcement effect of multiwalled carbon nanotubes in epoxy matrix composites

AbstractThe carbon nanotube possesses outstanding physical properties. Theoretically, adding carbon nanotubes into a polymer matrix can remarkably improve the mechanical properties of the polymer matrix. In the present work, a series of composites was prepared by incorporating multiwalled carbon nanotubes (MWNTs) into an epoxy resin. The influences of MWNT content and curing temperature on the flexural properties of the epoxy resin were investigated. The results showed that a very low MWNT content should be used to ensure homogeneous dispersion of MWNTs in the epoxy matrix. A higher MWNT content may lead to deteriorated mechanical properties of the composites because of the aggregation of MWNTs. A decline in the flexural properties of the neat epoxy resin with increasing curing temperature was found. However, under the same curing conditions, improvement in flexural properties was observed for the composite with the low MWNT content and a mild curing temperature. The improvement was far beyond the predictions of the traditional short‐fiber composite theory. In fact, this improvement should be attributed to the retarding effect of MWNTs on the curing reaction of epoxy matrix. Therefore, the improvement in the flexural properties was only a pseudoreinforcement effect, not a nano‐reinforcement effect of the MWNTs on the epoxy resin. Perhaps, it is better for MWNTs to be used as functional fillers, such as electrical or thermal conductive fillers, than as reinforcements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3664–3672, 2006

Electrical and Heating Properties of Nickel-coated Carbon Filler filled Plane Heater

Polymer composites filled with electrical conductive fillers are used in various industrial fields, and some of these materials show a positive temperature coefficient resistivity (PTC). This phenomenon is ascribed to volume expansion of the matrix polymer. By applying the PTC effect, these electrically conductive materials are able to be used as self-temperature control plane heater.In this study, new type of plane heater, different from ordinary plane heaters, with a rigid network structure filled with conductive fillers was prepared by a new processing method. First of all, the characteristics of the matrix urethane resin such as curing conditions and thermomechanical properties were investigated. This resin mixed with short nickel coated carbon fibers having different fiber lengths or aspect ratios was processed in to thin sheets and cured. The relationship between resistivity and fiber content and the influence of environmental temperature on resistivity of these composites were investigated experimentally. The relationship between heating properties and resistivity of the materials under supplied voltage and also the influence of environmental temperature on heating temperature were also discussed.