Multi-walled Carbon Nanotube/polystyrene Research Articles

Theoretical modeling and experimental verification of percolation threshold with MWCNTs’ rotation and translation around a growing bubble in conductive polymer composite foams

Foaming is a potential method to prepare high-performance, lightweight, composite materials with enhanced electrical properties. Here, a theoretical model and its experimental verification are presented to assess the evolution of electrical percolation threshold and conductivity as a bubble grows during the foaming of conductive filler/polymer composites. The filler networks were changed by translation and rotation of filler particle during bubble growth that was presented by void fraction increase. The evolution of percolation threshold with filler network was estimated using a Monte Carlo approach. The model results showed that the percolation threshold decreased, and the electrical conductivity increased for void fraction values less than 20%, beyond which the percolation threshold started to increase. Furthermore, a series of polystyrene/multiwalled carbon nanotubes (PS/MWCNTs) composite foams were fabricated at various void fractions matching the parameters in modeling. At an optimum void fraction of approximately 17%, the percolation threshold of the foamed samples was decreased by 20%, from 0.6 vol% down to 0.48 vol%. Further increases in the void fraction increased the percolation threshold. The simulation prediction was in good agreement with the experimental results. The model offers a valuable tool to better understand the electrical behavior and can be used in the design of conductive polymer composite foams with rod-like conductive fillers.

Synergistic effect of multiwalled carbon nanotubes and an intumescent flame retardant: Toward an ideal electromagnetic interference shielding material with excellent flame retardancy

ABSTRACTTo shield undesirable electromagnetic waves caused by electronic devices and simultaneously resolve the flame safety of the electronic components, an electromagnetic interference (EMI) shielding material with excellent flame‐retardant properties is urgently needed. The synergistic effect of the intumescent flame retardant (IFR) and multiwalled carbon nanotubes (MWCNTs) for polystyrene (PS) nanocomposites prepared by melt blending was investigated. The results show that addition of certain amounts of IFRs facilitated the dispersion of MWCNTs in the PS matrix, and the percolation threshold of the MWCNTs in the PS matrix also decreased from 1.67 ± 0.05 to 1.29 ± 0.04 wt %. Moreover, the EMI shielding efficiencies (SEs) of the PS–MWCNT–IFR composites were consistently higher than those of the PS–MWCNT composites without the addition of the IFRs at the same MWCNT content; this indicated that the synergistic effect of the MWCNTs and IFRs effectively improved the EMI SE of the PS–MWCNT–IFR composites. Furthermore, the limiting oxygen index (LOI) testing results show that the LOI values of the PS–MWCNT composites were consistently higher than 27%; this indicated that the PS–MWCNT composites effectively met the needs of flame safety; this indicated that the PS–MWCNT–IFR composite is a novel and promising candidate for an ideal EMI shielding material with excellent flame‐retardant properties for today's electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45088.

Investigation on the physical properties of multiwalled carbon nanotube–polystyrene nanocomposites treated with 2,3-hydroxy-2-naphthoic acid

In continuation to our previous work, the current investigation focuses on the effect of static applied pressure on the electrical and dielectric properties of multiwalled carbon nanotube (MWCNT)–polystyrene (PS)/2,3-hydroxy-2-naphthoic acid (β-HNA) nanocomposites. Additionally, optical properties of the nanocomposites are also investigated together with other further electrical, dielectric, and mechanical properties. Adding fixed amount of β-HNA (1.0 wt%) to MWCNTs enhances the MWCNT dispersion, reduces the percolation threshold to about 0.8 wt%, and increases the electrical conductivity up to eight orders of magnitude. The direct current (DC) and alternating current (AC) electrical properties of 1.0 wt% MWCNT–PS composites are investigated as a function of applied pressure. It is found that the current level increases while impedance values decrease with applied pressure during the cycle and the loading–unloading cycle has almost followed the same route indicating its reproducibility. Also the obtained results demonstrate that such a composite might act as pressure-sensitive conductive composite. Mechanical results show that the addition of MWCNTs (treated with β-HNA) to the neat PS increases the tensile strength and yield stress of the neat PS by about 12.39% and 12.53%, respectively, while the elastic modulus decreases by about 3.10%. However, further addition of MWCNTs decreases all mechanical parameters of prepared composites and these composites became more brittle. Besides, optical results indicate an enhancement in the neat polymer ultraviolet and visible absorption and a reduction in its optical energy gap (by about 14.1%) upon addition of 1.0 wt% MWCNTs (treated with β-HNA).

UV and thermally stable polystyrene-MWCNT superhydrophobic coatings

A facile method for ultraviolet (UV) and thermally stable polystyrene-multiwalled carbon nanotubes (PS-MWCNT) superhydrophobic coatings was demonstrated by a simple spray coating method. The superhydrophobicity was understood by an increase in micro/nano roughness with the addition of MWCNTs. Surface morphology of the coatings showed protrusion like structure. The wetting behavior of the coatings was studied as a function of temperature, and it is observed that the coatings were superhydrophobically stable up to 250 °C. A transformation of superhydrophobic to superhydrophilic state is achieved at 300 °C. The coatings remained superhydrophobically stable when it was subjected to UV-irradiation and water immersion of 50 h. Thermogravimetric analysis showed a small shift (10°) towards higher temperature region with an addition of MWCNTs, suggesting the presence of weak interactions between PS and MWCNT, which is also supported by Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy studies. Both hydrophilic and superhydrophobic coatings find potential applications in our daily life. Copyright © 2016 John Wiley & Sons, Ltd.

Impact of foaming on the broadband dielectric properties of multi-walled carbon nanotube/polystyrene composites

This study investigated the impact of foaming on the broadband dielectric properties of multi-walled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites. Different carbon nanotube concentrations were prepared by blending of a 20 wt.% MWCNT/PS masterbatch and pure PS using a twin-screw extruder. A chemical blowing agent was used to foam the nanocomposites in a micro injection molding machine. Compression molding was applied to fabricate unfoamed nanocomposites for comparison purposes. Comparing the dielectric properties of unfoamed and foamed nanocomposites showed that foaming increased the percolation threshold, reduced DC and AC conductivities, widened the insulator–conductor transition window, and reduced the dissipation factor of the MWCNT/PS composites. These were attributed to deteriorated conductive network and inferior dispersion and distribution of MWCNTs coming from the presence of foam cells in the nanocomposites. The obtained results propose foaming as a promising technique to improve the dielectric properties of MWCNT/polymer composites.

Synergistic effect of MWCNTs and graphite powder on the properties of polymer nanocomposites

Multi-walled carbon nanotube/polystyrene (MWCNT/PS), graphite powder/polystyrene (GP/PS) and multi-walled carbon nanotube-graphite powder/polystyrene (M-G/PS) nanocomposites with different contents of carbon materials were prepared by bulk radical polymerization. The products were pressed into slices to prepare specimens for electrical conductivity testing. All of the nanocomposites demonstrated good electrical conductivity. Compared to MWCNTs/PS and GP/PS composites, the M-G/PS composites showed a good synergistic effect between the MWCNTs and GP, and the electrical conductivity of M-G/PS was higher than that of GP/PS. To investigate the structure and morphology of the grafted carbon nano-materials, samples were submitted to Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) after being extracted with toluene. The results show that some polystyrene was grafted onto the surfaces of the MWCNTs, GP and M-G, which is likely responsible for the increase in the electrical conductivity of the composites. Furthermore, the mechanical properties of the M-G/PS nanocomposites increased with the M/G ratio. (C) 2014 Elsevier B.V. All rights reserved.

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

AbstractThe 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.

Micromechanical scribing and indentation behavior of injection-molded polymeric carbon nanotube (CNT) nanocomposites

Polymeric carbon nanotube (CNT) nanocomposites have unique mechanical, electrical, and thermal properties. Anisotropy can be induced depending on the alignment of the CNT fillers within polymeric composites, which is known to affect material properties. In order to investigate the effects of CNT alignments in micromechanical scribing using a single crystal diamond tool, a microindenter–scriber system was developed. Multiwalled carbon nanotube–polystyrene (MWCNT–PS) samples with varying CNT concentrations were prepared through a microinjection molding process, where the injection enables the partial alignment of CNTs in the flow direction through high shear stress. A mechanistic scribing force model was proposed based on the material properties that could be obtained using the microindentation techniques. Scribing experiments were performed in the parallel and perpendicular directions to the CNT alignment. Forces in three axes were measured and analyzed to identify three unknown parameters—the shearing, plowing, and adhesion friction coefficients. The resulting coefficients for scribing perpendicular to the CNT alignment showed distinguishable trends from scribing parallel to the CNT alignment as the CNT loadings increased. Their linear trends in relation to the material properties identified from indentation techniques can be used to predict microscribing parameters and resulting cutting forces, in combination with the proposed mechanistic model.

Improving immunosensor performance through oriented immobilization of antibodies on carbon nanotube composite surfaces

We report the straightforward oriented covalent attachment of antibodies (Abs) on the surface of carboxylated multiwalled carbon nanotube-polystyrene (MWCNT-PS) materials. The combination of this composite material, applied as a robust electrochemical transducer platform, and its covalent functionalization with Abs in a controlled way by means of a two-step process, could contribute to the development of highly sensitive immunosensor devices. Using the simple and versatile carbodiimide chemistry, Abs were attached to the carboxylic groups of the MWCNT-PS composite surfaces via their superficial amine groups. By taking into account the Ab isoelectric point and the net charge of the composite surface, we engineered an immobilization process to achieve the oriented binding of the Ab molecules by favoring an ionic pre-adsorption step before covalent binding occurred. Thus, the antigen binding capacity of the attached Abs was enhanced by up to 10 times with respect to the capacity estimated for a random spatial distribution of these molecules. The proposed strategy would also serve as a model for the efficient biofunctionalization of other carboxylated carbon-based polymer composite materials with potential applications in the biosensor field.

Orientation Structures in Injection-Molded Pellets of Polystyrene/Carbon Nanotube Nanocomposites

The orientation structures of both carbon nanotubes (CNTs) and polymer molecular chains in the skin–core structure of polystyrene/multiwalled carbon nanotube (PS/MWCNT) nanocomposite melt-injection-molded pellets were examined. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images clearly show the MWCNT preferred orientation along the melt shearing direction, while polarized Raman spectroscopy results consolidate the MWCNT preferred orientation in each of the skin, medium, and core layers of the injection-molded pellets. By infrared dichroism measurements, a preferred orientation of the PS side groups (phenyl rings) perpendicular to the melt shearing direction was deduced at all depths of the present injection-molded nanocomposite pellet. Meanwhile, the MWCNTs have little effect on the random orientation of the PS main chain (−CH2– groups) with a dichroic ratio near unity.

Rheological and electrical percolation thresholds of carbon nanotube/polymer nanocomposites

AbstractPercolation thresholds of multiwalled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites (NC) were determined by rheology and electrical conductivity. The percolation threshold found by electrical conductivity was 0.5% carbon nanotubes (CNT) and that by mechanical spectroscopy and relaxation measurements was 0.9% CNT. These results together with those reported in the literature show several types of percolation thresholds, depending on the average filler–filler (CNT and/or aggregates) distance in a polymer matrix. A distance close to polymer gyration radius corresponds to a “soft” rheological threshold (PC rheosoft). Close contacts between fillers giving rise to a conductive path corresponds to an electrical threshold (PC elec). At high filler concentration, fillers form a network, corresponding to a “rigid” rheological threshold (PC rheorigid). These thresholds depend on the filler content and follow the order: PC elecsoft < PC elec < PC rheorigid. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Facile and green method for polystyrene grafted multi-walled carbon nanotubes and their electroresponse

Polystyrene (PS) microspheres with a mean diameter of 69nm were prepared by emulsion polymerization. The PS microspheres were successfully decorated to multi-walled carbon nanotubes (MWNTs) induced by benzoyl peroxide in water during a high temperature refluxing process under nitrogen atmosphere. The as-prepared multi-walled carbon nanotube/polystyrene (MWNT/PS) nanocomposites were characterized by FTIR spectroscopy, Raman spectroscopy, SEM, TEM, differential scanning calorimetry (DSC), and electrical resistance measurements. The results reveal that PS microspheres are mainly covalently grafted onto the walls of MWNTs. The PS-decorated MWNTs show high solubility in toluene and xylene without sedimentation after 24h. With MWNTs in the hybrids, PS achieved a considerable increase in electrical conductivity and glass-transition temperature (Tg). In particular, the obtained MWNT/PS composites were examined for electrorheological (ER) fluids, which showed thin and dense chains of particles after the application of an electric field. The facile and environmentally friendly technique presented in the present study could be an effective and promising method for the functionalization of MWNTs by other polymers.

Ni filled flexible multi-walled carbon nanotube–polystyrene composite films as efficient microwave absorbers

In this letter, we report flexible, non corrosive, and light weight nickel nanoparticle@multi-walled carbon nanotube–polystyrene (Ni@MWCNT/PS) composite films as microwave absorbing material in the frequency range of S band (2-4 GHz). Dielectric permittivity and magnetic permeability of composites having 0.5 and 1.5 wt. % filler amount were measured using the cavity perturbation technique. Reflection loss maxima of −33 dB (at 2.7 GHz) and −24 dB (at 2.7 GHz) were achieved for 0.5 and 1.5 wt. % Ni@MWCNT/PS composite films of 6 and 4 mm thickness, respectively, suggesting that low concentrations of filler provide significant electromagnetic interference shielding.

Carbon nanotube composite peptide-based biosensors as putative diagnostic tools for rheumatoid arthritis

This work reports on the fabrication and performance of a simple amperometric immunosensor device to be potentially used for the detection of serum anti-citrullinated peptide antibodies (ACPAs), which are specific for rheumatoid arthritis (RA) autoimmune disease. Sera of RA patients contain antibodies to different citrullinated peptides and proteins such as fibrin or filaggrin. Herein, a chimeric fibrin–filaggrin synthetic peptide (CFFCP1) was used as a recognition element anchored to the surface of a multiwalled carbon nanotube–polystyrene (MWCNT–PS) based electrochemical transducer. The transducer fabrication process is described in detail together with its successful electrochemical performance in terms of repeatability and reproducibility of the corresponding amperometric response. The resulting immunosensor approach was initially tested in sera of rabbits previously inoculated with the synthetic peptide and eventually applied to the detection of ACPAs in human sera. A comparative study was carried out using control serum from a blood donor, which demonstrated the selectivity of the immunosensor response and its sensitivity for the detection of anti-CFFCP1 antibodies present in RA patients.

The strain sensing and thermal–mechanical behavior of flexible multi-walled carbon nanotube/polystyrene composite films

The strain sensing and thermal–mechanical behaviors of well dispersed multi-walled carbon nanotube/polystyrene (MWCNT/PS) composite films with different wt.% of carbon nanotubes were analyzed. The thermal–mechanical properties are studied using a dynamical mechanical analyzer and the results give their storage modulus (E′) and loss modulus (E″) as a function of temperature. We found an increase in E′ of up to 122% at 80 °C for a 6 wt.% MWCNT/PS composite compared to PS. The glass transition temperature increased significantly with an increase in MWCNTs concentration. The strain sensing behavior of the films is measured by applying an axial load over film which is attached to a brass specimen. The composite films exhibit excellent strain sensing behavior for different MWCNT contents. The result shows that an electromechanical response of the composite films varies linearly with applied strain even at high strains.

Conductivity percolation of carbon nanotubes (CNT) in polystyrene (PS) latex film

In this study, the effect of multiwalled carbon nanotubes (MWNT) on film formation behaviour and electrical conductivity properties of polystrene (PS) latex film was investigated by using the photon transmission technique and electrical conductivity measurements. Films were prepared by mixing PS latex with different amounts of MWNTs, varying in the range between 0 and 20 wt%. After drying, MWNT content films were separately annealed above the glass transition temperature (Tg) of PS, ranging from 100 to 270 °C, for 10 min. To monitor film formation behavior of PS–MWNT composites, transmitted light intensity, Itr, was measured after each annealing step. The surface conductivity of annealed films at 170 °C was measured and found to increase dramatically above a certain fraction of MWNT (4 wt%) following the percolation theory. This fraction was defined as the percolation threshold of conductivity, Rc. The conductivity scales with the mass fraction of MWNT as a power law with exponent 2.27, which is extremely close to the value of 2.0 predicted by percolation theory. In addition, the increase in Itr during annealing was explained by void closure and interdiffusion processes. Film formation stages were modeled and the corresponding activation energies were measured.

Preparation and characterization of thermally conductive polystyrene/carbon nanotubes composites

AbstractThermally conductive polystyrene (PS)/multi‐walled carbon nanotubes (MWNTs) nanocomposites was prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in PS, MWNTs were chemically functionalized with poly(styrene‐co‐maleic anhydride) (SMA) (MWNT‐g‐SMA), which had benzene group and exhibited strong affinity with PS. The thermal conductive properties of PS increased and the mechanical properties decreased in presence of MWNTs, while by addition of MWNT‐g‐SMA, the properties of the composites can be improved to some extent. The thermal conductivity can reach 0.89 W/m K for the composite with 33.3 vol % MWNT‐g‐SMA, which was four times higher than that of neat PS. A linear increase of the thermal conductivity was observed with increasing MWNTs‐g‐SMA content, and the Maxwell–Eucken model and the Agari model were used for theoretical evaluation. Compared with MWNT‐OH, MWNT‐g‐SMA with larger diameter exhibited diffused boundary with the PS matrix, resulting from the strong interfacial bonding of the two phases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A facile gemini surfactant-improved dispersion of carbon nanotubes in polystyrene

Debundling and dispersion of carbon nanotubes (CNTs) are very important for preparation of polymer/CNT nanocomposites. In the present study, a self-prepared gemini surfactant, 6,6′-(butane-1,4-diylbis(oxy))bis(3-nonylbenzenesulfonic acid), is employed to achieve homogeneous and stable dispersion of multi-walled carbon nanotubes (MWNTs) in organic solvent and subsequent polystyrene (PS)/MWNT nanocomposite. Sedimentation, optical microscopy and transmission electron microscopy studies demonstrate that the gemini surfactant can greatly improve the dispersion and stabilization of MWNTs in toluene. Scanning electron microscopic images clearly confirm the homogenous dispersion of individual MWNTs in PS. In addition, desired enhanced electrical conductivity and thermal stability of the nanocomposite relative to those of the neat PS are obtained.

Plasma-activated multi-walled carbon nanotube–polystyrene composite substrates forbiosensing

Carbon nanotube–polymer composites have shown to be suitable materials for thefabrication of electrochemical transducers. The exposed surface of these materials iscommonly passivated by a very thin layer of the polymer component that buries theconductive carbon particles. Working with multi-walled carbon nanotube–polystyrene(MWCNT–PS) composite structures, it was previously described how a simple low poweroxygen plasma process produced an effective etching of the composite surface,thereby exposing the conductive surface of CNTs. This work shows how thisplasma process not only gave rise to a suitable composite conductive surface forelectrochemical sensing but simultaneously exposed and created a high density ofoxygen-containing functional groups at both the CNT and the PS components,without affecting the material’s mechanical stability. These chemical groups couldbe effectively modified for the stable immobilization of biological receptors. Adetailed chemical characterization of the plasma-activated composite surface waspossible using x-ray photoelectron spectroscopy. The material reactivity towards thetethering of a protein was studied and protein–protein interactions were thenevaluated on the modified composite transducers by scanning electron microscopy.Finally, an amperometric immunosensor approach for the detection of rabbitImmunoglobulin G target analyte was described and a minimum concentration of3 ng ml−1 was easily measured.

Polystyrene composites containing crosslinked polystyrene‐multiwalled carbon nanotube balls

AbstractCrosslinked polystyrene‐multiwalled carbon nanotube (PS‐MWCNT) balls, which act as conductive microfillers, were prepared by the in situ suspension polymerization of styrene with MWCNTs and divinyl benzene (DVB) as a crosslinking agent. The diameters of the synthesized crosslinked PS‐MWCNT balls ranged from 10 to 100 μm and their electrical conductivity was about 7.7 × 10−3 S/cm. The morphology of the crosslinked PS‐MWCNT balls was observed by scanning electron microscopy and transmission electron microscopy. The change in the chemical structure of the MWCNTs was confirmed by Raman spectroscopy and Fourier transform infrared spectroscopy. The mechanical and electrical properties of the PS/crosslinked PS‐MWCNT ball composites were investigated. It was found that the tensile strength, ultimate strain, Young's modulus, and impact strength of the PS matrix were enhanced by the incorporation of the crosslinked PS‐MWCNT balls. In addition, the mechanical properties of the PS/crosslinked PS‐MWCNT ball composites were better than those of the PS/pristine MWCNT composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008