Papers by Mohammed Al-Saleh
Diamond and Related Materials
Journal of Thermoplastic Composite Materials
The effects of polycaprolactone (PCL) viscosity and carbon nanotubes (CNT) content on the microst... more The effects of polycaprolactone (PCL) viscosity and carbon nanotubes (CNT) content on the microstructure, morphology development, tensile strength, and electrical percolation behavior of CNT/polylactic acid (PLA)/PCL blends were investigated. PLA/PCL blends with a volume ratio of 80/20 were prepared using a low viscosity PCL (PCL1) and a high viscosity PCL (PCL2). The microstructure analysis showed finer dispersion of PCL2 than PCL1 within the PLA matrix. The addition of CNT changed the PLA/PCL morphology from dispersed to co-continuous due to the localization of the nanotubes in the PCL domain (i.e. the minor domain). In addition, the introduction of CNT reduced the PCL domain size and improved the adhesion at the PLA/PCL interface. For the electrical percolation behavior, PLA/PCL2 blend exhibited a percolation threshold concentration (EPTC) of 0.5 wt.% CNT compared to 1.0 wt.% CNT for the PLA/PCL1 blend. This remarkably lower EPTC for the PCL2-based blend is in line with the micro...
Journal of Macromolecular Science, Part B
Well-dispersed metal nanowire/polymer nanocomposites with low electrical percolation threshold an... more Well-dispersed metal nanowire/polymer nanocomposites with low electrical percolation threshold and improved surface electrical resistivities on the order of 1×10-2-1.0×10 2 Ohm•cm have been prepared. Nanowire/polystyrene nanocomposites were prepared by hot-compression for electromagnetic interference shielding characterization, and the effect of Cu nanowire concentration (0.2-3.0 vol. %) on the EMI shielding effectiveness was studied. The EMI shielding effectiveness was correlated with the dc electrical conductivity of the nanocomposites. Cu-nanowire/polystyrene nanocomposites show outstanding performance compared to composites prepared using traditional fillers (eg. stainless steel, metal plated C-fibers) or nanofillers (eg. carbon nanofibers, nanotubes). Thin specimens of these low filler concentration nanocomposites are an alternative to thicker specimens of conventional filled composites used for EMI.
Materials & Design, 2016
The effect of carbon nanotubes (CNTs) in improving the strengthening efficiency of carbon fiber/e... more The effect of carbon nanotubes (CNTs) in improving the strengthening efficiency of carbon fiber/epoxy composites retrofitted reinforced concrete (RC) beams was investigated. A total of sixteen simply supported RC beams were prepared and tested under four-point loading. The incorporation of CNTs within the systems was done by modifying the epoxy resin using CNTs and/or coating the carbon fiber sheets with CNT enriched sizing agent. The effects of epoxy modification with CNTs, incorporation of CNT enriched sizing agent, anchorage length, and number of retrofitting layers were investigated through crack patterns, failure modes, load-deflection curves, and scanning electron microscopy (SEM) micrographs of fractured surfaces. Experimental results showed that using CNT modified epoxy resin enhanced the ultimate load and stiffness of retrofitted beams. The enhancement efficiency highly depends on the level of dispersion of CNT, anchorage length, and number of retrofitting layers. SEM characterization showed that CNTs could improve the adhesion at the concrete/epoxy interface and carbon fiber/epoxy interface leading to improvement in the load transfer and ultimate load of the strengthened beams.
Journal of Macromolecular Science, Part B, 2021
Synthetic Metals, 2020
Abstract In this work, the influence of polymer structure on the electrical resistivity of polyme... more Abstract In this work, the influence of polymer structure on the electrical resistivity of polymer composites filled with carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), or carbon black (CB) was investigated. An amorphous polymer, polystyrene (PS), and a semi-crystalline polymer, polypropylene (PP), of similar viscosities were selected to investigate the effect of polymer matrix structure on the composites’ electrical resistivity. The composites were prepared by melt mixing in a small batch mixer. CNT dispersion in PS was better than that in PP, and the electrical resistivity of CNT/PS was lower than that of CNT/PP. For example, the electrical resistivity of the 1 vol% CNT/PS and 1 vol% CNT/PP were 13 Ω c m and 120 Ω c m , respectively. However, no significant difference in the electrical resistivity and state of dispersion for both CB-based and GNP-based composites were observed. For the CNT-based composites, it can be speculated that the better dispersibility of CNT particles within the PS matrix has greater influence on the construction of the three-dimensional network than the volume exclusion effect possessed by the PP semi-crystalline polymer.
Materials Research Express, 2019
Materials Research Express, 2019
Nanocomposites are advanced engineering materials with multifunctional characteristics and numero... more Nanocomposites are advanced engineering materials with multifunctional characteristics and numerous applications in the packaging, automotive, construction, and energy sectors. In this work, the effects of nanofiller geometry on the processing behavior, interfacial interaction, and electrical percolation behaviors of melt-mixed polystyrene (PS) nanocomposites were investigated. This paper also reports on the synergistic influence of incorporating multi-nanofiller mixture on the electrical resistivity of polymer nanocomposites. Two nanofillers of different geometries and electrical conductivities, namely carbon nanotubes (CNTs) and high-structure carbon black (CB), were used to prepare the nanocomposites. CNTs have a rod-like (1D) shape, whereas CB is characterized by an irregular-branched shape. Because CNTs have higher aspect ratio and electrical conductivity than CB, the CNT-based composites exhibited lower electrical resistivity and electrical percolation threshold than the CB-based composites. The analysis of the percolation behaviors showed that the network formation in the CNT/PS and CB/PS composites can be attributed to the kinetic percolation rather than the statistical percolation. Most interestingly, the CNT:CB/PS composites with a CNT:CB mass ratio of 75:25 showed higher electrical conductivity than the CNT-based and the CB-based composites, revealing a synergetic effect on the electrical properties at this nanofiller ratio.
Nanotechnology, 2018
Nanostructured polymeric materials based on conductive nanofillers have promising applications in... more Nanostructured polymeric materials based on conductive nanofillers have promising applications in the energy storage field owing to the extraordinary characteristics of the nanofillers. Conductive nanofillers, such as graphene nanoplatelets, are characterized by small size, extraordinary surface area to volume ratio, high aspect-ratio and extremely low electrical resistivity. In this work, the dielectric behaviors and the corresponding energy storage capabilities of high aspect-ratio carbon nanofiller/polymer composites were reviewed. At the electrical percolation point, a conductive composite exhibits a sudden and remarkable enhancement in dielectric constant and dielectric loss. The challenge is to maintain the increase in dielectric constant while preventing the increase in dielectric loss. Various physical and chemical methodologies have been followed to overcome this challenge including surface chemistry modifications, physical alignment of nanofillers and utilizing of hybrid mixtures. Promising results were reported to minimize the energy loss due to the conductive network formation. Nanocomposites with a dielectric constant of 103 and dielectric loss of only 0.08 were successfully fabricated. However, more work is still needed for a further enhancement in dielectric constant and reduction in the energy loss and to improve the storage capabilities of the nanocomposites.
Construction and Building Materials, 2018
Thermal performance, fire resistance, strengths and microstructure of nanoclay modified cement mo... more Thermal performance, fire resistance, strengths and microstructure of nanoclay modified cement mortar were investigated. Degradation in strengths due to heating was reduced when nanoclay was added. Width and density of hairline cracks due to heating were decreased in presence of nanoclay. The addition of nanoclay enhanced the thermal behavior of cement mortar.
KSCE Journal of Civil Engineering, 2018
Improved methods of-PNS synthesis by adjusting basic parameters intended for obtaining naphthalen... more Improved methods of-PNS synthesis by adjusting basic parameters intended for obtaining naphthalene formaldehyde oligomers with optimal molar mass distribution. Resulting product is polymethylene naphthalenesulphonate-PNS-K4 (5-7, 6-6-polymethylene naphthalene-sodium sulphonate) with improved cement mortars plasticizing properties. Plasticizing effect:-PNS-K4, as an additive, is viewed in comparison to the known Kratasol plasticizer (produced by Superplast). By its plasticizing properties, effect on the strength and on the kinetics of concrete hardening, the analyzed PNS-K4 is not inferior to Krasatol performance and shows similar results.
Journal of Macromolecular Science, Part B, 2015
The effects of organically modified clay (OMC) incorporation on the microstructure and the electr... more The effects of organically modified clay (OMC) incorporation on the microstructure and the electrical and mechanical properties of polypropylene (PP)/polyethylene (PE) blends filled with carbon nanotubes (CNT) were investigated. All blends were prepared by melt mixing in a batch mixer. The microstructures were characterized by scanning electron microscopy. In the OMC:CNT filled blends, the CNT were found to selectively localize within the PE phase, while the clay particles were observed in the PP phase. The electrical resistivity of OMC:CNT filled blends did not show any significant change as a result of the clay addition since it was localized in the CNT-free phase. On the other hand, the addition of clay degraded the blends' mechanical properties due to the poor adhesion between the OMC and the PP matrix.
Composites Science and Technology, 2017
Creating electrically conductive polymer composites with extremely low nanofiller concentration b... more Creating electrically conductive polymer composites with extremely low nanofiller concentration by melt compounding is a major research challenge. At low nanofiller concentration, the valuable properties of polymers are preserved and the feasibility of the composite is promoted. In this work, an organically modified clay (OMC) was utilized to alter the structure and consequently the electrical resistivity of carbon nanotubes (CNT)/polypropylene (PP) composite. As a result of OMC incorporation, the electrical percolation threshold concentration (EPTC) was reduced from 1.
Polymer-Plastics Technology and Engineering, 2017
In this work, the effects of carbon nanotube (CNT)-modified epoxy and CNT-enriched sizing agent o... more In this work, the effects of carbon nanotube (CNT)-modified epoxy and CNT-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 CNT and sizing agent were fabricated by hand layup-vacuum bagging process. Scanning electron microscopy (SEM) analysis was conducted to unveil the relation between the macro-properties and the composites' microstructure. Experimental results showed that the CNT-modified epoxy/CF composite showed 20% enhancements in the Young's modulus compared to the pristine epoxy/CF composite. The SEM analysis of the fracture surfaces revealed that incorporating CNT in 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 (IFSS) and load transfer between the matrix and the fabrics and consequently the tensile characteristics of the formulated composite.
Construction and Building Materials, 2017
h i g h l i g h t s CNTs modified CFRP was used to repair heat damaged RC beams. Heating RC beams... more h i g h l i g h t s CNTs modified CFRP was used to repair heat damaged RC beams. Heating RC beams significantly affected their flexural behavior. Using nano-modified CFRP partially recover strength capacity of damaged beams. The adhesion between carbon fiber/ epoxy and epoxy/concrete interfaces was enhanced.
Materials and Structures, 2017
This paper reports on the influence of carbon nanotubes (CNT) on the axial load capacity of heat-... more This paper reports on the influence of carbon nanotubes (CNT) on the axial load capacity of heat-damaged RC columns repaired with carbon fiber reinforced (CFRP) composites. The nanotubes were incorporated in the composites by using CNT-modified epoxy and/or coating the carbon fiber sheet with sizing agent enriched with CNT. Twenty-two reinforced concrete columns were casted, heated at 500 and 600°C, repaired with FRP or nano-modified FRP composite, and then tested. The mode of failure, ultimate load, initial stiffness, and toughness were analyzed. Scanning electron microscopy (SEM) characterization was performed to explore the morphology of the tested specimens. The results revealed that the load capacity and the toughness of the repaired columns were enhanced when CNT-modified resin and/or CNT-enriched sizing agent were incorporated in the composite. Compared with the unmodified FRP sheets, SEM micrographs showed more debris were attached to the FRP sheets in the cases where CNT were incorporated in the composite reflecting an enhancement in the adhesion at the epoxy/fiber interface thus the load transfer process.
Synthetic Metals, 2016
Polypropylene (PP)/polyethylene (PE) blends filled with 5 vol% graphene nanoplatelets: carbon nan... more Polypropylene (PP)/polyethylene (PE) blends filled with 5 vol% graphene nanoplatelets: carbon nanotube (GNP:CNT) hybrid nanofiller were prepared by melt mixing. The blends' microstructure and the influence of GNP:CNT volume ratio on the electrical, electromagnetic interference (EMI) shielding and tensile strength were investigated. The scanning electron microscopy analysis showed that the CNT and GNP are localized in the PE phase. The electrical conductivity and EMI shielding were found to increase with the increase in CNT volume fraction due to the 1D geometry of the CNT that is more effective than the 2D geometry of the GNP in building conductive networks. This finding indicates that not only the nanofiller conductivity but also the nanofiller geometry should be considered in designing hybrid nanocomposite materials. Moreover, the tensile strength was found to increase with the decrease in GNP:CNT volume ratio due to the good adhesion between the CNT particles and the PE phase compared to the almost no adhesion between the GNP particles and the PE phase.
Journal of Electronic Materials, 2016
Graphene nanoplatelet (GNP)–polystyrene nanocomposites filled with up to 20 wt.% GNPs were prepar... more Graphene nanoplatelet (GNP)–polystyrene nanocomposites filled with up to 20 wt.% GNPs were prepared by melt mixing. The microstructure, direct-current (dc) electrical percolation behavior, and dielectric characteristics were investigated as functions of frequency. In addition, the effects of dc bias on the complex impedance and charge transport mechanisms were explored. The dc electrical percolation curve showed a gradually transition from the insulating to conducting state. At 15 wt.% GNP loading and frequency greater than 104 Hz, the nanocomposite exhibited dielectric constant and loss factor of 180 and 0.11, respectively, revealing remarkable storage capabilities at high frequencies. For nanocomposites filled with 12 wt.% to 20 wt.% GNPs, the alternating-current conductivity was found to follow the universal dynamic response behavior, implying electron conduction due to tunneling in addition to direct contact between GNPs.
Construction and Building Materials, 2016
Bond-slip behavior between concrete and FRP composites was improved using CNT. Using CNT modified... more Bond-slip behavior between concrete and FRP composites was improved using CNT. Using CNT modified epoxy enhanced both bond strength and ultimate slippage. Bond enhancement between FRP and concrete depends on fiber and epoxy type and bond area. SEM images showed that CNTs could improve the adhesion at the FRP/concrete interface.
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Papers by Mohammed Al-Saleh