Mohammed H. Al-Saleh

Highly electrically conductive and high performance EMI shielding nanowire/polymer nanocomposites by miscible mixing and precipitation

Metal nanowire/polymer nanocomposites are advanced materials for electrically conductive applications. Metal nanowires have high surface area, high aspect ratios, and high electrical conductivity, which are critical for the synthesis of conductive polymer nanocomposites using extremely low amounts of conductive filler. In this work, lightweight, thin, and highly conductive copper nanowire/polystyrene nanocomposites were prepared using a novel method of nanocomposite preparation termed miscible solvent mixing and precipitation (MSMP). Suspensions of high aspect ratio copper nanowires were mixed with polystyrene solutions to produce polymer nanocomposites with segregated nanowire networks resembling cell-like structures. Highly electrically conductive networks of nanowires were obtained beyond a percolation threshold of ϕc = 0.67 vol% and percolated nanocomposites showed electrical conductivities up to 104 S m−1, which exceeds the conductivity range generally reported for carbon nanofiller-based nanocomposites. The significant potential of these nanocomposites for electrical applications like electromagnetic interference (EMI) shielding was further demonstrated. Metal nanowire/polymer nanocomposites sheets of 0.21 mm in thickness exhibited EMI SE of more than 20 dB for copper nanowire concentrations of only 1.3 vol%.

X-band EMI shielding mechanisms and shielding effectiveness of high structure carbon black/polypropylene composites

The electromagnetic interference (EMI) shielding effectiveness (SE) and EMI shielding mechanisms of high structure carbon black (HS-CB)/polypropylene (PP) composites in the X-band frequency range were studied. Composite plates with three different thicknesses and five different electrical conductivities were studied. The reflection loss and absorption loss of the composites were quantified based on the electromagnetic radiation power balance. The results showed that for HS-CB/PP composites, absorption loss contribution to the overall attenuation is more than the contribution of the reflection loss. The ability of the theoretical model to predict the EMI shielding by reflection and absorption was found to be a function of the shielding plate thickness and conductivity.

Impedance characteristics and conductivity of CNT/ABS nanocomposites

Electrical impedance characteristics of multi-walled carbon nanotube (MWCNT)/acrylonitril‐butadiene‐styrene nanocomposite was studied as a function of MWCNT concentration in the frequency range of 10 0 ‐10 6 Hz. The nanocomposites were prepared by solution processing and characterized to have good dispersion of the nanofiller within the polymer matrix as observed by the transmission electron microscopy. In the frequency range of 1‐10 4 Hz, the alternating current (ac) conductivity versus frequency plot of the 0.25wt% MWCNT nanocomposite exhibited a direct current (dc) plateau indicating that there is a segregated network within this nanocomposite. In the low-frequency region, the bode diagram of the real part of impedance and ac conductivity of the nanocomposites filled with 0.25wt% up to 4wt% MWCNT showed a frequency independent plateau followed by an increase obeying the universal dynamic response indicating that conduction in this MWCNT concentration range might be due to tunnelling in addition to the direct contact between filler nanoparticles. For nanocomposites filled with at least 7wt% MWCNT, the ac conductivity was frequency independent over the entire frequency range (up to 10 6 Hz) revealing that conduction is due to direct contact between nanoparticles.

Electrical and dielectric behaviors of dry-mixed CNT/UHMWPE nanocomposites:

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.

Electrical and electromagnetic interference shielding characteristics of GNP/UHMWPE composites

Conductive polymer composites (CPC) are attractive materials for a wide range of applications because of their weight, corrosion resistivity, design flexibility and low cost. In the present work, the electrical and electromagnetic interference (EMI) shielding characteristics of graphene nanoplatelets (GNP)/ultrahigh molecular weight polyethylene (UHMWPE) composites filled with up to 40 wt% GNP were investigated. In addition, the intrinsic conductivity of the GNP network was estimated based on the statistical power law and the rule of mixtures for randomly oriented filler particles in insulating matrix. Due to the formation of a segregated conductive network at the external surface of UHMWPE powder, an electrical percolation threshold of between 2 and 3 wt% GNP was obtained. At GNP loading of 15 wt%, the composite exhibited an EMI shielding effectiveness of 33 dB, corresponding to 99.95% blocking of the EMI.

Electrical Impedance Spectroscopic Study of CNT/Ethylene-alt-CO/Propylene-alt-CO Polyketones Nanocomposite

Impedance spectroscopy was utilized to investigate the dielectric properties, ac conductivity and charge transport mechanisms in propylene-alt-CO/ethylene-alt-CO (EPEC) random terpolymer filled with multi-walled carbon nanotubes (MWCNT) as a function of nanofiller content, frequency, and temperature. Equivalent resistor-capacitor (RC) circuit models were proposed to describe the impedance characteristics of the unfilled terpolymer and the nanocomposite at different temperatures. For the nanocomposites, the ac conductivity tended to be frequency independent at low frequencies. At high frequencies, the ac conductivity increased with frequency. The dc conductivity (i.e., plateau of the ac conductivity at low frequencies) at room temperature increased from 10−9 (Ω·m)−1 for the unfilled polymer to l0−3 (Ω·m)−1 for the 6 wt% MWCNT/EPEC nanocomposite. At low temperatures, the equivalent RC model for EPEC-0 and EPEC-2 was found to consist of a parallel RC circuit. However, for 6 wt% MWCNT/EPEC nanocomposite, an RC model consisting of an R/constant phase element (CPE) circuit and a resistor in series was required to describe the impedance behavior of the nanocomposite.

Utilizing Vacuum Bagging Process to Prepare Carbon Fiber/CNT-Modified-epoxy Composites with Improved Mechanical Properties

ABSTRACT In this work, the effects of carbon nanotube-modified epoxy and carbon nanotube-enriched sizing agent on the tensile properties and failure mode of unidirectional carbon fiber/epoxy composites were investigated. Laminates of carbon fiber/epoxy composites at different concentrations of carbon nanotube and sizing agent were fabricated by hand layup vacuum bagging process. Scanning electron microscopy analysis was conducted to unveil the relation between the macroproperties and the composites’ microstructure. Experimental results showed that the carbon nanotube-modified epoxy/carbon fiber composite showed 20% enhancements in the Young’s modulus compared to the pristine epoxy/carbon fiber composite. The scanning electron microscopy analysis of the fracture surfaces revealed that incorporating carbon nanotube into the epoxy matrix with utilizing the vacuum improves the interfacial bonding and minimizes the voids that act as crack initiators. This microstructure enhances the interfacial shear strength and load transfer between the matrix and the fabrics and consequently the tensile characteristics of the formulated composite. GRAPHICAL ABSTRACT

Effect of processing conditions on the dispersion, electrical, and mechanical properties of carbon nanotube/polypropylene nanocomposites

Carbon nanotube (CNT)/polypropylene nanocomposites with different levels of CNT dispersion were created by melt mixing in order to reveal the influence of nanofiller state of dispersion on the nanocomposites electrical and mechanical properties. Optical microscopy and transmission electron microscopy were used to analyze the microstructure of the nanocomposite. Melt mixing energy, melt viscosity, and shear stress were analyzed to understand the influence of processing conditions on the microstructure and electrical properties. CNT dispersion in the polypropylene matrix was enhanced by increasing the melt mixing time and/or rotation speed. The electrical conductivity was found to be very sensitive to the changes in the CNT level of dispersion, while the tensile strength and secant modulus did not show any significant response to the enhancement in the nanofiller state of dispersion.

Effect of Nanoclay on Expansive Potential of Cement Mortar due to Alkali-Silica Reaction

The impact of partial substitution of cement particles with nanoclay on the expansive potential of cement mortar due to alkali-silica reaction (ASR) was investigated. Portland cement was replaced by 0.5%, 1%, and 2% montmorillonite nanoclay. The effect of ASR on compressive strength, chemical composition, and microstructure of nanoclay-cement composites was evaluated. The accelerated mortar-bar method was followed to perform the ASR test according to ASTM C1567. The experimental results showed that the expansion of cement mortar due to ASR can be reduced by the addition of nanoclay. Two percent nanoclay was the only dosage among others used in this study that can mitigate the expansion. Furthermore, the ASR caused a marginal enhancement in compressive strength of mortar compared to the specimens cured in water. The gain in strength reached up to 10% for mortars contacting 2% nanoclay. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis did not detect the formation of any secondary products due to the ASR, revealing the similarity between ASR and the pozzolanic reaction for the first 14 days of the reaction. However, the microstructure of the mortars became denser and more homogeneous when a part of cement was replaced by nanoclay.

Effect of viscosity reducing agent on the properties of CNT/epoxy nanocomposites

Abstract Epoxy nanocomposites that are produced in a solvent-free environment suffer from the inadequate dispersion of nanofiller and poor interfacial interaction between the nanofiller and polymer matrix. In this work, the effect of replacing a portion of the epoxy resin with a viscosity reducing agent (VRA) on the structure, electrical and mechanical properties of carbon nanotube (CNT)/epoxy nanocomposite have been investigated. Optical microscopy (OM) and transmission electron microscopy (TEM) were used to characterize the structure of the nanocomposite at the microscale and nanoscale, respectively. For nanocomposites without VRA, it was found that the addition of CNT degrades the tensile strength and toughness; meanwhile, it enhances the flexural modulus, Young’s modulus and electrical conductivity of the nanocomposite. However, the addition of VRA retained the tensile strength of the epoxy system and maintained the improvements in flexural strength and electrical conductivity that have been achieved due to CNT addition.