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The enhancement of the electromagnetic interference shielding efficiency (EMI SE) for conductive polymer composites (CPCs) has garnered increasing attention. The shielding performance is influenced by conductivity, which is dependent on the establishment of effective conductive pathways. In this review, Schelkunoff's theory on outlining the mechanism of electromagnetic interference shielding was briefly described. Based on the mechanism, factors that influenced the electrical percolation threshold of CPCs were presented and three main kinds of efficient methods were discussed for establishing conductive pathways. Furthermore, examples were explored that highlighted the critical importance of such conductive pathways in attaining optimal shielding performance. Finally, we outlined the prospects for the future direction for advancing CPCs towards a balance of enhanced EMI SE and cost–performance. [ABSTRACT FROM AUTHOR]

This review delves into the progress made in additive manufacturing through the incorporation of conductive fillers in nanocomposites. Emphasizing the critical role of percolation and conductivity, the study highlights advancements in material selection, particularly focusing on carbon nanotubes with low percolation thresholds. The practical applications of these nanocomposites in additive manufacturing polymer composites are explored, emphasizing the understanding of percolation thresholds. Furthermore, the present review paper investigates the potential of these materials as lightweight alternatives for electromagnetic interference shielding (EMI), particularly in key sectors such as automotive and aerospace industries. The integration of advanced materials, modeling techniques, and standardization is discussed as pivotal for successful implementation. Overall, the review underscores the significant strides in enhancing electrical properties and electromagnetic interference shielding capabilities through the strategic use of conductive filler nanocomposites in additive manufacturing. [ABSTRACT FROM AUTHOR]

The enhancement of the electromagnetic interference shielding efficiency (EMI SE) for conductive polymer composites (CPCs) has garnered increasing attention. The shielding performance is influenced by conductivity, which is dependent on the establishment of effective conductive pathways. In this review, Schelkunoff’s theory on outlining the mechanism of electromagnetic interference shielding was briefly described. Based on the mechanism, factors that influenced the electrical percolation threshold of CPCs were presented and three main kinds of efficient methods were discussed for establishing conductive pathways. Furthermore, examples were explored that highlighted the critical importance of such conductive pathways in attaining optimal shielding performance. Finally, we outlined the prospects for the future direction for advancing CPCs towards a balance of enhanced EMI SE and cost–performance.

The increasing demand for flexible electronics and portable gadgets has resulted in an increase in the amount of emitted EM radiation in recent years. Conductive carbon black (VCB XC 72) is a quasi-graphitic structure of clustered carbon particles that was deemed an ideal material for the development of extremely flexible electromagnetic interference (EMI) shielding materials. The sequential solution and melt mixing process has been used to generate a flexible and recyclable zinc oxide cross-linked, and VCB XC 72 nanofiller reinforced EMI shielding material. The ionic cross-linked network, created by other self-clustering ion duplets of Zn2+ ions, gave rise to the amazing recycling and reprocessing abilities of carboxylated acrylonitrile butadiene rubber (XNBR). The cross-linked XNBR and conductive black combination formed a tunable inferential framework that provided absorption, reflection, and multiple reflection shielding mechanisms. Based on the findings of the morphological study, it has been determined that the scattered and distributed carbon black clusters included inside XNBR rubber are creating the pathway for electrical hopping. As a result, the electrical percolation threshold has been lowered, and EMI shielding has significantly improved. The rubber composites had improved thermal characteristics in addition to having outstanding mechanical performances. Hopefully, these findings will pave the way forward for the development of smart electronic devices and environmentally friendly EMI shielding materials. [ABSTRACT FROM AUTHOR]

In this research work, a two-dimensional model to predict the electrical percolation threshold (EPT) of the polymer/graphene-based nanocomposites in different concentrations of the randomly dispersed inclusions in various polymer matrices is introduced using the finite element method (FEM). The predicted EPT values were validated by other experimental results for different nanocomposites. Results showed that the electrical conductivity of different nanocomposites is significantly related to the percentage weight of the reinforcing phase in the polymer matrix. Furthermore, the addition of graphene-based nano-fillers in the polymer matrix caused a decrease in the tunneling distance in nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract The use of high contents of carbon fillers in polymeric composites may decrease the mechanical properties of the polymeric matrices, as well as reduce their processability and increase the production costs of antistatic packaging used in the electronic industry. Therefore, it is of great technological interest the research on alternative approaches to produce polymer composites with low electrical percolation threshold. In this way, this review article focuses on the discussion of the main factors that interfere in the electrical percolation threshold of electrically conductive polymer composites, such as the aspect ratio of the carbon fillers and its particle size, the compatibility between the composite phases, the crystallinity degree of the polymeric matrix, the processing route and the location of fillers in multi‐phase polymer blends. Additionally, the review article reports the latest studies related to the obtainment of polymer composites with low percolation threshold contents and produced with different types of carbon fillers.

Composites made up of microparticles embedded in a polymeric matrix have attracted increasing attention due to the possibility of tailoring their physical properties by adding the adequate quantity of fillers. As the concentration of these fillers increases, their connectivity changes drastically at a given threshold and therefore the electrical, thermal and optical properties of these composites are expected to exhibit a percolation effect. In this work, the thermal and electrical conductivities along with the emissivity of composites composed of carbonyl-iron microparticles randomly distributed in a polyester resin matrix are measured, for volume fractions ranging from 0 to 0.55. It is shown that both the thermal and electrical conductivities increase with the particles' concentration, such that their percolation threshold appears at volume fractions of 0.46 and 0.38, respectively. The emissivity, on the other hand, decreases as the fillers' concentration increases, such that it exhibits a substantial decay at a volume fraction of 0.41. The percolation threshold of the emissivity is thus higher than that of the thermal conductivity, but lower than the electrical conductivity one. This dispersion on the percolation concentration is justified by the different physical mechanisms required to activate the electrical, thermal, and optical responses of the considered composites. The obtained results thus show that the percolation phenomenon can efficiently be used to enhance or reduce the physical properties of particulate composites. [ABSTRACT FROM AUTHOR]

It can efficiently enhance electrical conductivity and electromagnetic interference (EMI) shielding performance to construct segregated structures in conductive polymer composites (CPCs). However, it can also deteriorate mechanical properties due to weak interfacial interaction between matrixes and fillers. So segregated structures CPCs that polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) was coated by ABS/multi‐walled carbon nanotubes (ABS/MWCNTs) were prepared by solution‐mechanical mixing method. The surface resistivity of the segregated composites achieved 105 Ω/sq with only 0.05 wt% of MWCNTs and was lower than composites prepared by melt and solution mixing methods. Tensile strength of the segregated composites was nearly 40 MPa. The EMI shielding values of the segregated composites with 7 wt% of MWCNTs were 50 to 80 dB as high as the uniform structure composites with 10 wt% of MWCNTs between 30 MHz and 1 GHz electromagnetic frequency. All the results displayed that this work provided a novel and efficient method to produce segregated conductive composites for antistatic and EMI shielding applications. [ABSTRACT FROM AUTHOR]

The electrical conductivity of polymer nanocomposites plays a critical role in applications like aerospace and electromagnetic shielding. Electrical conductivity and other electromagnetic parameters of carbon nanotube (CNT)‐based epoxy nanocomposites are being analysed in this work for their suitability in electromagnetic shielding. Unfilled epoxy and CNT epoxy nanocomposite samples with various filler loadings are prepared. Impedance measurements are conducted over the frequency range of 20 Hz–10 MHz. Micromechanics model is used for the theoretical estimation of electrical conductivity of CNT‐based epoxy nanocomposites. Interface thickness in the conventional model is modified to avoid the overestimation of electrical conductivity. DC conductivity of nanocomposites determined experimentally is found to obey classical law of percolation theory and percolation threshold is determined to be 0.17 wt% which agrees well with theoretical value of 0.18 wt% obtained using modified micromechanics model. AC conductivity is found to obey universal dynamic response. Dipolar polarisation mechanism is prominent in the tested frequency range whose frequency of occurrence increases with CNT content due to a greater number of interfaces formed between CNT and epoxy. CNT epoxy nanocomposites are found to have negative permeability thus acting as absorbers in electromagnetic shielding. [ABSTRACT FROM AUTHOR]

The present study outlines a reliable approach to determining the electrical conductivity and elasticity of highly oriented electrospun conductive nanofibers of biopolymers. The highly oriented conductive fibers are fabricated by blending a high molar mass polyethylene oxide (PEO), polycaprolactone (PCL), and polylactic acid (PLA) with polyaniline (PANi) filler. The filler-matrix interaction and molar mass (M) of host polymer are among governing factors for variable fiber diameter. The conductivity as a function of filler fraction (φ) is shown and described using a McLachlan equation to reveal the electrical percolation thresholds (φc) of the nanofibers. The molar mass of biopolymer, storage time, and annealing temperature are significant factors for φc. The Young’s modulus (E) of conductive fibers is dependent on filler fraction, molar mass, and post-annealing process. The combination of high orientation, tunable diameter, tunable conductivity, tunable elasticity, and biodegradability makes the presented nanofibers superior to the fibers described in previous literature and highly desirable for various biomedical and technical applications.

The effect of the crystallization of polypropylene (PP) forming an immiscible polymer blend with polystyrene (PS) containing conductive multi-wall carbon nanotubes (MWCNTs) on its electrical conductivity and electrical percolation threshold (PT) was investigated in this work. PP/PS/MWCNTs composites with a co-continuous morphology and a concentration of MWCNTs ranging from 0 to 2 wt.% were obtained. The PT was greatly reduced by a two-step approach. First, a 50% reduction in the PT was achieved by using the effect of double percolation in the blend system compared to PP/MWCNTs. Second, with the additional thermal treatments, referred to as slow-cooling treatment (with the cooling rate 0.5 °C/min), and isothermal treatment (at 135 °C for 15 min), ultra-low PT values were achieved for the PP/PS/MWCNTs system. A 0.06 wt.% of MWCNTs was attained upon the use of the slow-cooling treatment and 0.08 wt.% of MWCNTs upon the isothermal treatment. This reduction is attributed to PP crystals’ volume exclusion, with no alteration in the blend morphology.

Epoxy resins containing multi-wall carbon nanotubes (MWCNTs) have proven to be suitable for manufacturing promising self-sensing materials to be applied in the automotive and aeronautic sectors. Different parameters concerning morphological and mechanical properties of the hosting matrices have been analyzed to choose the most suitable system for targeted applications. Two different epoxy precursors, the tetrafunctional tetraglycidyl methylene dianiline (TGMDA) and the bifunctional bisphenol A diglycidyl ether (DGEBA) have been considered. Both precursors have been hardened using the same hardener in stoichiometric conditions. The different functionality of the precursor strongly affects the crosslinking density and, as a direct consequence, the electrical and mechanical behavior. The properties exhibited by the two different formulations can be taken into account in order to make the most appropriate choice with respect to the sensing performance. For practical applications, the choice of one formulation rather than another can be performed on the basis of costs, sensitivity, processing conditions, and most of all, mechanical requirements and in-service conditions of the final product. The performed characterization shows that the nanocomposite based on the TGMDA precursor manifests better performance in applications where high values in the glass transition temperature and storage modulus are required.

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)–polyvinylpyrrolidone (PVP) films. We demonstrate—starting from the design and synthesis of the layers—how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO2 substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05–0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05–0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite’s longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold’s critical role in the resistive relative-humidity sensors’ design and functioning is clearly emphasized.

Organic–inorganic ternary nanohybrids consisting of oxidized-single walled carbon nanohorns-SnO2-polyvinylpyrrolidone (ox-SWCNH/SnO2/PVP) with stoichiometry 1/1/1 and 2/1/1 and ox-SWCNH/ZnO/PVP = 5/2/1 and 5/3/2 (all mass ratios) were synthesized and characterized as sensing films of chemiresistive test structures for ethanol vapor detection in dry air, in the range from 0 up to 50 mg/L. All the sensing films had an ox-SWCNH concentration in the range of 33.3–62.5 wt%. A comparison between the transfer functions and the response and recovery times of these sensing devices has shown that the structures with ox-SWCNH/SnO2/PVP = 1/1/1 have the highest relative sensitivities of 0.0022 (mg/L)−1, while the devices with ox-SWCNH/SnO2/PVP = 2/1/1 have the lowest response time (15 s) and recovery time (50 s) for a room temperature operation, proving the key role of carbonic material in shaping the static and dynamic performance of the sensor. These response and recovery times are lower than those of “heated” commercial sensors. The sensing mechanism is explained in terms of the overall response of a p-type semiconductor, where ox-SWCNH percolated between electrodes of the sensor, shunting the heterojunctions made between n-type SnO2 or ZnO and p-type ox-SWCNH. The hard–soft acid–base (HSAB) principle supports this mechanism. The low power consumption of these devices, below 2 mW, and the sensing performances at room temperature may open new avenues towards ethanol sensors for passive samplers of environment monitoring, alcohol test portable instruments and wireless network sensors for Internet of Things applications.

In this paper, we produced composites of high-density polyethylene (PE)/polypropylene (PP) filled with graphene by melt compounding. Comparing composites produced in three processing sequences, we explored whether the sequence improved the composites' electrical conductivity. The (graphene/PE)/PP composite, prepared by simultaneous compounding, exhibited an electrical percolation threshold of 1.25 vol.%. In contrast, the (graphene/PP)/PE composite, prepared by blending the graphene with PP first and then blending the graphene/PP with PE, had a much lower electrical percolation threshold at less than 0.83 vol.%. At its percolation threshold, the (graphene/PP)/PE composite had a conductivity about two orders of magnitude higher than the (graphene/PE)/PP composite. We attribute this difference in conductivity to differences in the graphene distributions in the composites. In the (graphene/PE)/PP composite, the graphene sheets were selectively dispersed in the PE phase; in the (graphene/PP)/PE composite, some of the graphene was localized at the interface of the PE/PP blend. We also showed how the different processing sequences affected the composites' measured rheological and mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, the anticorrosion properties of a waterborne polyurethane dispersion (WPU) containing polyaniline (PAni) were investigated and discussed considering the electrical percolation threshold (EPT) of this mixture. For that, easily dispersible poly(styrene sulfonic acid)-doped PAni (PAni:PSS) was incorporated into an anionic WPU at contents ranging from 1 to 8 wt%. Free-standing films of PAni:PSS/WPU reached the EPT at 6 wt% (4.8 v.%) of PAni:PSS. The mixtures remained stable and without signs of PAni dedoping. Based on the electrical behavior curve, PAni:PSS/WPU coatings were prepared below (1, 2, 3 wt%), close to (5 wt%), at (6 wt%) and above the EPT (8 wt%). The coatings were applied on ground low-carbon steel panels and evaluated regarding their contact angle, adhesion, and anticorrosion performance in electrochemical tests. The coatings prepared below the EPT presented higher hydrophobicity, good wet adhesion, and higher open circuit potential (OCP) and impedance modulus in the low frequency range (|Z| 10 mHz). The best overall performance was achieved at 3 wt% of PAni:PSS which presented OCP values in the range of 34 ± 11 mV for 144 h and initial |Z| 10 mHz of 108 Ω.cm2. These coatings also presented a colorimetric feature of changing color as the corrosion progressed. Meanwhile, the coatings containing PAni:PSS quantities close, at and above the EPT, i.e., at 5, 6 and 8 wt% presented high porosity, poor wet adhesion, and intense blistering. They also presented OCP values in the region of active corrosion and impedance spectra typical of coatings with poor barrier properties. These results indicate that, the formation of conducting networks within the insulating matrix is not necessarily a condition that must be met for a coating containing PAni achieve an optimal anticorrosion performance. [Display omitted] • Coatings performed better below the electrical percolation threshold (EPT). • Having a conducting network of PAni does not imply better anticorrosion protection. • The EPT was a better predictor of the coating's performance than the CPVC. • The coatings acted as a colorimetric sensor of the corrosion progression. • PAni.PSS in the coatings led to the formation of a passive oxide layer. [ABSTRACT FROM AUTHOR]

Abstract: Evolution of DC conductivity with double-walled carbon nanotube concentration in a polyamide 11 matrix displays the electrical percolation phenomenon. The percolation threshold is observed for this composite at 0.85wt.%. Thermal, mechanical and dielectric manifestations of the glass transition have been investigated as a function of carbon nanotube content. Thermal and mechanical analyses have shown a depression of the glass transition temperature or its mechanical manifestation at the percolation threshold. Regarding the dielectric modulus, three distinct behaviors (below, at, and above percolation threshold) have been observed. A discussion about the interactions between the polymer matrix and the conductive fillers will be proposed to further the understanding of the discontinuity of physical properties at the percolation threshold. [Copyright &y& Elsevier]

Abstract: Since the emergence of large aspect ratio and multifunctional conductive fillers, such as carbon nanotubes, graphene nanoplates, etc., conductive polymer composites (CPCs) have attracted increasing attention. Although the morphological control of conductive networks in CPCs has been extensively investigated as an important issue for the preparation of high performance CPCs, recent extensive progress has not been systematically addressed in any review. It has been observed that the morphological control of conductive networks during the preparation of CPCs has crucial influence on the electrical properties of these composites. Several methods have been shown to be able to control the network structure, and thus, tune the electrical properties of CPCs, including the use of shear, polymer blends, thermal annealing, mixed filler, latex particle etc. Moreover, many novel and exciting applications have been extensively investigated for CPCs, such as stretchable conductor, electroactive sensors, shape memory materials and thermoelectric materials, etc. Therefore, the morphological control of conductive network in CPCs is reviewed here. Issues regarding morphology characterization methods, morphological control methods, resulted network morphology and electrical properties are discussed. Furthermore, the use of CPCs as electroactive multifunctional materials is also reviewed. [Copyright &y& Elsevier]

Carbon nanotube (CNT)/ultrahigh-molecular weight polyethylene (UHMWPE) nanocomposite with an electrical percolation threshold of only 0.1 wt% was prepared by simple dry mixing followed by compression molding. The nanocomposite microstructure, direct current and alternating current (AC) electrical conductivities, conduction mechanisms, and dielectric properties in the 101–105 Hz frequency range have been investigated. Due to the localization of the nanofiller at the surface of UHMWPE powder particles, a segregated microstructure within the polymer matrix was created. Nanocomposites filled with 0.125–0.5 wt% CNT were found to follow the typical universal dynamic response behavior, and the characteristic frequency was found to increase with the increase in CNT concentration. At CNT concentration ≥ 0.5 wt%, the AC conductivity was found to be frequency independent over the entire frequency range studied. [ABSTRACT FROM AUTHOR]

In this study, a qualitative equivalence between the electrical percolation threshold and the effective thermal conductivity of composites filled with cylindrical nanofillers has been recognized. The two properties are qualitatively compared on a wide range of aspect ratios, from thin nanoplatelets to long nanotubes. Statistical continuum theory of strong-contrast is utilized to estimate the thermal conductivity of this type of heterogeneous medium, while the percolation threshold is simultaneously evaluated using the Monte Carlo simulations. Statistical two-point probability distribution functions are used as microstructure descriptors for implementing the statistical continuum approach. Monte Carlo simulations are carried out for calculating the two-point correlation functions of computer generated microstructures. Finally, the similarities between the effective conductivity properties and percolation threshold are discussed. [ABSTRACT FROM AUTHOR]

Carbon nanotubes have been the subject of extensive research during the past decade because of their exceptional properties. These tiny nanostructures have eventually paved their way into the exciting and promising field of organic electronics, which is expected to dominate the area of low cost and flexible electronics in the near future. We have prepared multiwall carbon nanotube (MWNT) and poly(3,4-ethylenedioxythiophene):poly(styrenesulphonic acid) (PEDOT:PSS) based nanocomposites using different concentrations of MWNTs. These nanocomposites have been characterized using SEM, AFM, absorption spectroscopy, and electrical characterization methods. The SEM micrographs clearly reveal that the nanotubes are quasi uniformly dispersed in huge quantities throughout the polymer matrix. They also show the wetting of the nanotubes by the polymer. It is observed that the solution processed MWNT-PEDOT:PSS nanocomposite based films exhibit improved, higher current, and lower turn-on voltage as compared to pure PEDOT:PSS based films. On the basis of percolation theory, a low electrical percolation threshold value of 0.1 wt% was obtained for this nanocomposite system, signifying the formation of a continuous conductive network at a very low MWNT concentration. The ease of fabrication of the nanocomposite (solution processed), higher current, lower turn-on voltage and low electrical percolation threshold value, make it an excellent candidate for flexible electronics applications, which will dominate the electronics scenario in the near future. [ABSTRACT FROM AUTHOR]

Abstract: The outstanding properties of carbon nanotubes have generated scientific and technical interests in the development of nanotube-reinforced polymer composites. Therefore, we investigated a novel mixing approach for achieving a good dispersion of multiwalled carbon nanotubes (CNTs) in a rubber blend. In this approach the CNTs were incorporated into a 50:50 blend of solution-styrene–butadiene rubber and butadiene rubber. First, the CNTs were predispersed in ethanol and then this CNT–alcohol suspension was mixed with the rubber blend at elevated temperature. The rubber nanocomposites prepared by such method exhibit significantly enhanced physical properties already at very low nanotube concentrations. Additionally, we have analysed the dielectric and thermal properties of the compound. The high aspect ratio of the carbon nanotubes enabled the formation of a conductive percolating network in these composites at concentrations below 2wt.%. In contrast to the electrical conduction behaviour, the thermal conductivity of the composites has not been influenced significantly by the presence of carbon nanotubes. Dynamic mechanical analysis indicates that the incorporation of CNTs affects the glass transition behaviour by reducing the height of the tan δ peak considerably. Above the glass transition temperature the storage modulus has been increased after incorporation of a small amount of CNTs. Finally, the ‘Payne effect’, an indication of filler–filler interactions, was observed at very low concentrations of CNT in the rubber matrix. [Copyright &y& Elsevier]

The present study outlines a reliable approach to determining the electrical conductivity and elasticity of highly oriented electrospun conductive nanofibers of biopolymers. The highly oriented conductive fibers are fabricated by blending a high molar mass polyethylene oxide (PEO), polycaprolactone (PCL), and polylactic acid (PLA) with polyaniline (PANi) filler. The filler-matrix interaction and molar mass (M) of host polymer are among governing factors for variable fiber diameter. The conductivity as a function of filler fraction (φ) is shown and described using a McLachlan equation to reveal the electrical percolation thresholds (φc) of the nanofibers. The molar mass of biopolymer, storage time, and annealing temperature are significant factors for φc. The Young's modulus (E) of conductive fibers is dependent on filler fraction, molar mass, and post-annealing process. The combination of high orientation, tunable diameter, tunable conductivity, tunable elasticity, and biodegradability makes the presented nanofibers superior to the fibers described in previous literature and highly desirable for various biomedical and technical applications. [ABSTRACT FROM AUTHOR]

Polymer composites based on poly(methyl metacrylate)/multi-wall carbon nanotubes, (PMMA/MWNT), were prepared by the solvent cast technique from dispersions of MWNT in PMMA solutions. Three different solvents like toluene, chloroform and acetone were selected to solve PMMA, covering a broad range of Hansen solubility parameters. Composite mixing was done by sonication of solutions with MWNT in a broad concentration range up to 20wt.% of MWNT. Electrical conductivity of composites as a function of MWNT concentration was measured. The different percolation thresholds were found for used systems like PMMA/solvent/MWNT which were found to be related to values of Hansen solubility parameters. Increasing the dispersion component, together with lower values of polar and hydrogen bonding components, leads to a lower value of percolation threshold. [ABSTRACT FROM AUTHOR]

The effect of the crystallization of polypropylene (PP) forming an immiscible polymer blend with polystyrene (PS) containing conductive multi-wall carbon nanotubes (MWCNTs) on its electrical conductivity and electrical percolation threshold (PT) was investigated in this work. PP/PS/MWCNTs composites with a co-continuous morphology and a concentration of MWCNTs ranging from 0 to 2 wt.% were obtained. The PT was greatly reduced by a two-step approach. First, a 50% reduction in the PT was achieved by using the effect of double percolation in the blend system compared to PP/MWCNTs. Second, with the additional thermal treatments, referred to as slow-cooling treatment (with the cooling rate 0.5 °C/min), and isothermal treatment (at 135 °C for 15 min), ultra-low PT values were achieved for the PP/PS/MWCNTs system. A 0.06 wt.% of MWCNTs was attained upon the use of the slow-cooling treatment and 0.08 wt.% of MWCNTs upon the isothermal treatment. This reduction is attributed to PP crystals' volume exclusion, with no alteration in the blend morphology. [ABSTRACT FROM AUTHOR]

Epoxy resins containing multi-wall carbon nanotubes (MWCNTs) have proven to be suitable for manufacturing promising self-sensing materials to be applied in the automotive and aeronautic sectors. Different parameters concerning morphological and mechanical properties of the hosting matrices have been analyzed to choose the most suitable system for targeted applications. Two different epoxy precursors, the tetrafunctional tetraglycidyl methylene dianiline (TGMDA) and the bifunctional bisphenol A diglycidyl ether (DGEBA) have been considered. Both precursors have been hardened using the same hardener in stoichiometric conditions. The different functionality of the precursor strongly affects the crosslinking density and, as a direct consequence, the electrical and mechanical behavior. The properties exhibited by the two different formulations can be taken into account in order to make the most appropriate choice with respect to the sensing performance. For practical applications, the choice of one formulation rather than another can be performed on the basis of costs, sensitivity, processing conditions, and most of all, mechanical requirements and in-service conditions of the final product. The performed characterization shows that the nanocomposite based on the TGMDA precursor manifests better performance in applications where high values in the glass transition temperature and storage modulus are required. [ABSTRACT FROM AUTHOR]

Organic–inorganic ternary nanohybrids consisting of oxidized-single walled carbon nanohorns-SnO2-polyvinylpyrrolidone (ox-SWCNH/SnO2/PVP) with stoichiometry 1/1/1 and 2/1/1 and ox-SWCNH/ZnO/PVP = 5/2/1 and 5/3/2 (all mass ratios) were synthesized and characterized as sensing films of chemiresistive test structures for ethanol vapor detection in dry air, in the range from 0 up to 50 mg/L. All the sensing films had an ox-SWCNH concentration in the range of 33.3–62.5 wt%. A comparison between the transfer functions and the response and recovery times of these sensing devices has shown that the structures with ox-SWCNH/SnO2/PVP = 1/1/1 have the highest relative sensitivities of 0.0022 (mg/L)−1, while the devices with ox-SWCNH/SnO2/PVP = 2/1/1 have the lowest response time (15 s) and recovery time (50 s) for a room temperature operation, proving the key role of carbonic material in shaping the static and dynamic performance of the sensor. These response and recovery times are lower than those of "heated" commercial sensors. The sensing mechanism is explained in terms of the overall response of a p-type semiconductor, where ox-SWCNH percolated between electrodes of the sensor, shunting the heterojunctions made between n-type SnO2 or ZnO and p-type ox-SWCNH. The hard–soft acid–base (HSAB) principle supports this mechanism. The low power consumption of these devices, below 2 mW, and the sensing performances at room temperature may open new avenues towards ethanol sensors for passive samplers of environment monitoring, alcohol test portable instruments and wireless network sensors for Internet of Things applications. [ABSTRACT FROM AUTHOR]

In this study, reliability-based robust design optimization (RBRDO) for polymer nanocomposites (PNCs) design is conducted to secure the reliability of design conditions concerning the electrical percolation threshold and carbon nanotube (CNT) aspect ratio as well as the robustness for electrical conductivity. CNT diameter and length are known as following the lognormal and Weibull distributions respectively. To reflect the different probability distributions of CNT geometry parameters and correlations between these random input variables, Nataf transformation is employed. By performing several case studies with the first-order reliability method (FORM)-based RBRDO approaches, the objective function exhibited a noteworthy change according to the correlation coefficients and the reliability and robustness for PNCs were satisfied concurrently. Furthermore, the highlight of this work is to provide a generic framework for practical PNC design and multi-objective optimization to enhance electrical performance efficiently. Image 1 • In-house code is developed for percolation simulation of polymer nanocomposites. • The effect of tunneling resistance is considered in developed percolation model. • Reliability-based robust design optimization carried out with Nataf transformation. • Our design accounts for reliability and robustness in electrical performance. • Our generic framework provides informed guidelines towards better PNC design. [ABSTRACT FROM AUTHOR]

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)-polyvinylpyrrolidone (PVP) films. We demonstrate-starting from the design and synthesis of the layers-how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO 2 substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05-0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05-0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite's longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold's critical role in the resistive relative-humidity sensors' design and functioning is clearly emphasized.

Background: Carbon nanotubes (CNTs) are attractive nanostructures in this regard, primarily due to their high aspect ratio coupled with high thermal and electrical conductivities. Consequently, CNT polymer composites have been extensively investigated for various applications, owing to their light weight and processibility. However, there have been several issues affecting the utilization of CNTs, such as aggregation (bundling) which leads to a non-uniform dispersion and poor interfacial bonding of the CNTs with the polymer, resulting in variation in composite performance, along with the additional issue of high cost of CNTs., Description: In this article, recent research and patents for polymer composites containing carbon nanomaterial are presented and summarized. In addition, a rationale for optimally designed carbon nanotube polymer composites and their applications are suggested. Above the electrical percolation threshold, a transition from insulator to conductor occurs. The percolation threshold values of CNT composite are dependent on filler shape, intrinsic properties of filler, type of polymer, CNT dispersion condition and so on. Different values of percolation threshold CNT polymer composites have been summarized. The difference in percolation threshold and conductivity of CNT composites could be explained by the degree of effective interactions between nanotubes and polymer matrix. The reaction between surface functional groups of CNTs and polymer could contribute to better dispersion of CNTs in polymer matrix. Consequently, it increased the number of electrical networks of CNTs in polymer, resulting in an enhancement of composite conductivity. In addition, to exfoliate nanotubes from heavy bundles, ultrasonication with proper solvent and three roll milling processes were used. Potential reactions of covalent bonding between functionalized CNTs and polymer were suggested based on the above rationale., Conclusion: Through the use of CNT functionalization, high aspect ratio CNTs, and proper fabrication, uniform dispersion of nanotubes in polymer can be achieved leading to considerable improvement in electrical conductivity and electromagnetic interference (EMI) shielding properties., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

The objectives of this work are to quantify the degree of multiwalled carbon nanotube (MWCNT) length reduction upon melt compounding and to demonstrate unambiguously that the length reduction is mainly responsible for the increase in electrical percolation threshold of the resulting composites. Polyolefin matrices of varying viscosities and different functional groups are melt compounded with MWCNTs. A simple method is developed to solubilize the polymer matrix and isolate the MWCNTs, enabling detailed imaging analysis. In spite of the perceived strength of the MWCNTs, the results demonstrate that the shear forces developed during melt mixing are sufficient to cause significant nanotube breakage and length reduction. Breakage is promoted when higher MWCNT contents are used, due to increased probability of particle collisions. Furthermore, the higher shear forces transmitted to the nanotubes in the presence of higher matrix viscosities and functional groups that promote interfacial interactions, shift the nanotube distribution toward smaller sizes. The length reduction of the MWCNTs causes significant increases in the percolation threshold, due to the loss of interconnectivity, which results in fewer conductive pathways. These findings are validated by comparing the experimental percolation threshold values with those predicted by the improved interparticle distance theoretical model.