Abozar Akbari

Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30–40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71±5 l m−2 hr−1 bar−1 for 150±15 nm thick membranes).

Suppressed Polysulfide Crossover in Li–S Batteries through a High-Flux Graphene Oxide Membrane Supported on a Sulfur Cathode

Utilization of permselective membranes holds tremendous promise for retention of the electrode-active material in electrochemical devices that suffer from electrode instability issues. In a rechargeable Li–S battery—a strong contender to outperform the Li-ion technology—migration of lithium polysulfides from the sulfur cathode has been linked to rapid capacity fading and lower Coulombic efficiency. However, the current approaches for configuring Li–S cells with permselective membranes suffer from large ohmic polarization, resulting in low capacity and poor rate capability. To overcome these issues, we report the facile fabrication of a high-flux graphene oxide membrane directly onto the sulfur cathode by shear alignment of discotic nematic liquid crystals of graphene oxide (GO). In conjunction with a carbon-coated separator, the highly ordered structure of the thin (∼0.75 μm) membrane and its inherent surface charge retain a majority of the polysulfides, enabling the cells to deliver very high initial dis...

The Effect of the Structure of Clay and Clay Modifier on Polystyrene-Clay Nanocomposite Morphology: A Review

Nanocomposites formation brings about an enhancement of many properties for polymers. They have attracted interests since they attain significant properties with far less clay content. It is generally assumed that exfoliation nanocomposites are preferred for the greatest increases in properties, but that is not correct in flame retardency properties. In this paper the effects of different types of clays and clay modifiers on final morphology of PS/clay nanocomposites were reviewed. Clay charge density and length, bulk, polarity, functional groups and polymerizability of the clay modifier are very significant in their efficiency and final morphology of PS/Clay nanocomposite.

Polylactic acid/polycaprolactone nanocomposite: Influence of montmorillonite and impact modifier on mechanical, thermal, and morphological properties

This article investigates the performance of polylactic acid (PLA)/polycaprolactone (PCL)/montmorillonite (MMT) nanocomposites toughened with metallocene-catalyzed linear low-density polyethylene (mLLDPE), in terms of mechanical, thermal, and morphological properties. All the results were compared and the influence of MMT and mLLDPE on the final properties was observed and reported. mLLDPE decreased the modulus and the strength of PLA/PCL and its nanocomposites due to its inherent lower rigidity compared to PLA/PCL nanocomposites. Moreover, incorporation of clay significantly increased mechanical and thermal stability of the nanocomposites. Scanning electron microscopic images confirmed that MMT acted as a compatibilizer, whereas it reduced the size of the droplets. It has been suggested that improvements in properties are related to good dispersion of clays within the matrix. However, further addition of MMT beyond 2 parts per hundred (phr) level decreases all the properties of PLA/PCL/mLLDPE/MMT nanocomposites. X-Ray diffraction patterns were used to discover the reason of reduction in the properties of PLA/PCL/mLLDPE/MMT at 4 phr. It was revealed that mLLDPE-toughened blends have intercalated structure below 4 phr MMT content as the interlayer spacing decreased at 4 phr MMT.

Mechanical and Thermal Properties of ABS/PVC Composites: Effect of Particles Size and Surface Treatment of Ground Calcium Carbonate

The objectives of this study are to determine the effects of particles size and surface treatment of ground calcium carbonate (GCC) on the mechanical and thermal properties of acrylonitrile butadiene styrene/poly(vinyl chloride) (ABS/PVC) (80:20) blends. The results showed GCC increased flexural modulus but decreased flexural and impact strength of the blend. Sample S2 containing stearate surface treated GCC showed the highest flexural modulus value while S1 with the smallest particles size was the highest for impact strength. GCC increased the thermal stability of ABS/PVC composites with S1 being the most effective, as indicated from the thermogravimetric analysis.

Epoxidized natural rubber toughened polylactic acid/talc composites: Mechanical, thermal, and morphological properties

The aim of present study is to develop a toughened polylactic acid/talc composite. Talc and epoxidized natural rubber (ENR-50) were compounded with polylactic acid using counter-rotating twin-screw extruder followed by preparation of samples through injection molding. The effect of silane-treated talc and epoxidized natural rubber on mechanical, thermal, and morphological properties of polylactic acid was investigated. The Young′s and flexural modulus of polylactic acid improved while the impact strength values dropped with increasing talc content (20–30 wt%) indicating that talc increased the stiffness of polylactic acid with a sacrifice in toughness. Subsequently, the blending of epoxidized natural rubber (20 wt%) to polylactic acid/talc (30 wt%) revealed that the impact strength of polylactic acid/talc composites improved 448% with considerable drop in Young’s and flexural modulus. Polylactic acid/talc/epoxidized natural rubber composite contains 60% polylactic acid, 30 wt% talc, and 10 wt% ENR display optimum stiffness and impact strength. Scanning electron micrographs demonstrates that talc agglomerates at higher loadings. Thermogravimetric anlaysis indicated that thermal stability of polylactic acid/talc composite was reduced by the addition of epoxidized natural rubber due to increasing talc agglomeration.

Ultrasensitive Strain Sensor Produced by Direct Patterning of Liquid Crystals of Graphene Oxide on a Flexible Substrate

Ultrasensitive flexible strain sensors were developed through the combination of shear alignment of a high concentration graphene oxide (GO) dispersion with fast and precise patterning of multiple rectangular features on a flexible substrate. Resistive changes in the reduced GO films were investigated under various uniaxial strain cycles ranging from 0.025 to 2%, controlled with a motorized nanopositioning stage. The devices uniquely combine a very small detection limit (0.025%) and a high gauge factor with a rapid fabrication process conducive to batch production.

Polylactic Acid Based Blends, Composites and Nanocomposites

Biopolymers are expected to be an alternative for conventional plastics due to the limited resources and soaring petroleum price which will restrict the use of petroleum based plastics in the near future. PLA has attracted the attention of polymer scientist recently as a potential biopolymer to substitute the conventional petroleum based plastics. The chapter aims to highlight on the recent developments in preparation and characterization of PLA blends (biodegradable and non-biodegradable blends), PLA composites (natural fiber and mineral fillers) and PLA nanocomposites (PLA/montmorillonite, PLA/carbon nanotubes and PLA/cellulose nanowhiskers).

Polylactic Acid (PLA) Carbon Nanotube Nanocomposites

In recent years, much attention has been paid to biodegradable polymers due to their wide range of applications in biomedical, packaging, agriculture fields and also economic and environmental consideration. Meanwhile, polylactic acid (PLA) is a more considerable biopolymer in comparison with other biopolymers. One of the most applicable methods to improve PLA performance is the combination of PLA with different materials. Today’s carbon nanotubes (CNTs) are a more interesting additive because of excellent mechanical, electrical, and magnetic properties as well as nanometer scale diameter and high aspect ratio. This chapter aims to highlight on the recent development in preparation and characterization of PLA/CNT nanocomposites and also reviews effective parameters on CNT dispersion in PLA matrix.

Polylactic acid (PLA) layered silicate nanocomposites

The depletion of fossil fuels and increased environmental awareness among peoples over the disposal of short-life plastics attracted the use of biodegradable and bio-based plastics for different application. Over the past decade, scientist has been showing sustainable research interest on biodegradable polymers as one of the solution to alleviate solid waste disposal problem and less dependency on petroleum-based plastics. PLA has attracted the attention of polymer scientist recently as a potential biopolymer to substitute the conventional petroleum-based plastics. The chapter aims to highlight on the recent developments in preparation and characterization of PLA/layered silicate nanocomposites.