Polyamide 66 nanocomposites based on organoclays treated with thermally stable phosphonium salts

Purification of bentonite clays and their modification with two thermally stable (alkyl and aryl) phosphonium organic salts were investigated. The organoclays were subsequently melt compounded with Polyamide 66 (PA66), with and without the use of an elastomeric compatibilizer. The morphology, melt flow, thermal stability, and mechanical properties of the binary and ternary nanocomposites were studied. The bentonite clay was purified by sedimentation, resulting in higher cation exchange capacity and thermal stability in comparison with unpurified clay. These were then used in the synthesis of two thermally stable organoclays by replacing the interlayer sodium cations with two (alkyl and aryl) phosphonium surfactant cations to circumvent the problem of low temperature decomposition of quaternary ammonium organoclays usually used in polymer nanocomposites. The organoclay with aliphatic groups showed more compatibility with PA66 in comparison with the organoclay with aromatic groups. Thus, the use of organoclay with aliphatic groups resulted in nanocomposites with higher tensile strength, higher modulus, higher elongation at break, and higher impact strength in comparison with the nanocomposites produced from the organoclay with aromatic groups. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of magnesium hydroxide nanofiller and its use for improving thermal properties of new poly(ether‐amide)

A new poly(ether‐amide; PEA) as a source of polymeric matrix, containing flexible ether group in the main chain was synthesized by direct polycondensation reaction of 1,2‐(4‐carboxy phenoxy)ethane with 4,4‐diaminodiphenyl ether in a medium consisting of N‐methyl‐2‐pyrrolidone, triphenyl phosphite, calcium chloride, and pyridine. The resulting PEA was characterized by gel permeation chromatography (GPC), ¹H NMR and FT‐IR spectroscopy. Magnesium Hydroxide (MH) nanostructure was synthesized by the reaction of magnesium sulfate and sodium hydroxide by sonochemical method. The MH particle was characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Then Mg(OH)₂ nanostructure was added to poly(ether‐amide) matrix and resulting nanocomposites were characterized by XRD, SEM, and Thermogravimetry Analysis (TGA). Thermal decomposition of the PEA shifted towards higher temperature in the presence of the magnesium hydroxide nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study of viscoelastic properties of nanocomposites of SiO2–acrylonitrile–butadiene–styrene

Nanocomposites of acrylonitrile–butadiene–styrene (ABS) and nanosilica with different nanoparticle sizes and various loadings are prepared. Rheological experiments such as frequency sweep, strain sweep, and rotational test are performed to investigate the influence of nanoparticle loading and size on the viscoelastic properties of the nanocomposites. The results show that nanocomposites with higher filler loading and smaller particle size have both higher storage and loss moduli. Moreover, the results indicate that the storage modulus is more sensitive than loss modulus to filler loading and nanoparticle size. The smaller nanoparticles and higher filler loadings lead to the enhancement of nanoparticle surface area so that the viscoelastic properties are intensified through increase of polymer chain adsorption on nanoparticle, and creation of a network structure in the nanocomposites. The network structure causes changes to the rheological behavior of the nanocomposite such as solid‐like behavior in the low‐frequency region and reduction of the Newtonian region. The scanning electron microscopy micrographs revealed that the particle aggregates increase with particle size reduction and increasing nanoparticle content. We also used a nonlinear optimization to obtain the parameters of a multimode Maxwell model for low nanofiller content ABS/SiO₂ nanocomposites and found the relaxation times of the polymer chains increased with increasing nanoparticle content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Extraordinarily high plastic deformation in polyurethane/silica nanoparticle nanocomposites with low filler concentrations

We have synthesized segmented polyurethane (SPU)/silica nanoparticle (SiNP) nanocomposites with extraordinarily high tensile strength and strain-at-break using an in-situ polymerization method with low SiNP concentrations. A 20-fold increase in strain-at-break compared with the pristine polymer has been achieved for the 0.5 wt% SiNP nanocomposites. A suite of characterization tools including transmission electron microscopy, ultra-small angle X-ray scattering, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis has been used to correlate the phase morphology, crystallization, and mechanical properties. The location of SiNP in the phase separated SPU is believed to be the main reason for the mechanical property enhancement.     

Self‐Assembly of Nanostructured,Complex, Multication Films via Spontaneous Phase Separation and Strain‐Driven Ordering

Spontaneous self‐assembly of a multication nanophase in another multication matrix phase is a promising bottom‐up approach to fabricate novel, nanocomposite structures for a range of applications. In an effort to understand the mechanisms for such self‐assembly, complimentary experimental and theoretical studies are reported to first understand and then control or guide the self‐assembly of insulating BaZrO₃ (BZO) nanodots within REBa₂Cu₃O_7–δ (RE = rare earth elements including Y, REBCO) superconducting films. The strain field developed around BZO nanodots embedded in the REBCO matrix is a key driving force dictating the self‐assembly of BZO nanodots along REBCO c‐axis. The size selection and spatial ordering of BZO self‐assembly are simulated using thermodynamic and kinetic models. The BZO self‐assembly is controllable by tuning the interphase strain field. REBCO superconducting films with BZO defect arrays self‐assembled to align in both vertical (REBCO c‐axis) and horizontal (REBCO ab‐planes) directions result in the maximized pinning and J_c performance for all field angles with smaller angular J_c anisotropy. The work has broad implications for the fabrication of controlled self‐assembled nanostructures for a range of applications via strain‐tuning.     

Virus‐Tethered Magnetic Gold Microspheres with Biomimetic Architectures for Enhanced Immunoassays

In immunoassays, non‐specific bindings to biosensing surfaces can be effectively prevented by formation of biocompatible and hydrophilic self‐assembled monolayer (SAM) on the surfaces. A thin gold (Au) layer on magnetic microspheres, 15 μm in diameter, enables facile SAM formation and thereby accepts second layer of filamentous virus scaffolds for the immobilization of functional proteins. The merger of the virus and SAM‐Au protected microspheres not only provides exceptionlly dense antibody loading, but also resembles biological cellular structures that enhance ligand‐receptor interactions. Site‐specific biotinylation of filamenous viruses allows formation of free‐standing virus threads (>1.0 × 10¹⁰) on streptavidin‐modified SAM‐Au microspheres. The augmented yield of antibody loading, due to the increased surface to volume ratio, on virus‐modified Au microspheres is confirmed by measuring fluorescence intensities. The bead‐based immunoassays for the detection of cardiac marker proteins exhibit increased sensitivity of virus‐Au microspheres, as low as 20 pg mL^?1 of cardiac troponin I in serum, and extremely low non‐specific adsorption when compared with bare polymer beads. This increased sensitivity due to filamentous morphology and SAM‐Au layer demonstrates the feasibility of merging viruses with non‐biological materials to yield biomimetic tools for the enhanced bead‐based immunoassays.     

Synthesis and characterization of polypyrrole/graphitic carbon nitride/niobium pentoxide nanocomposite for high-performance energy storage applications

Graphitic carbon nitride (GCN) has been employed as a supercapacitor electrode because of its high carbon-to-nitrogen ratio and flexible structure. However, its low surface area and poor conductivity continue to be obstacles for practical usage. GCN's electrochemical characteristics are enhanced by the hybrid structure it forms with polypyrrole and Nb₂O₅. The synthesized polypyrrole (Ppy)/GCN/niobium pentoxide (Nb₂O₅) (Ppy/GCN/Nb₂O₅) nanocomposite electrode was tested for supercapacitance by cyclic voltammetry (CV) and Alternating current impedance techniques in 6 M Potassium hydroxide(KOH) electrolyte. The Ppy/GCN/Nb₂O₅ is linked to a network of agglomerated GCN and Nb₂O₅ nanoparticles with additional spherical shapes. The specific capacitance of Ppy/GCN/Nb₂O₅ was determined to be 1177 Fg⁻¹ at a current density of 5 Ag⁻¹. The Ppy/GCN/Nb₂O₅ electrode in KOH has average specific energy and specific power densities of 33 Wh kg⁻¹ and 2991 W kg⁻¹, respectively. The electrode showed excellent capacitance-retention ability of 97% after 10,000 cycles. The results demonstrate the high stability and efficient performance of the Ppy/GCN/Nb₂O₅ electrode employed in supercapacitors. The performance of the Ppy/GCN/Nb₂O₅ electrode was found to be superior to those reported for other carbon-based materials.     

Self-cleaning antireflected surfaces based on treated PEO/SiO2 nanocomposite films

In this study, the polyethylene oxide (PEO)/SiO₂ nanoparticles (NPs) nanocomposite films with various SiO₂ NPs concentrations were prepared using an in situ formation of NPs in the polymer matrix for self-cleaning antireflected surface applications. The effect of SiO₂ NPs in PEO/SiO₂ NPs nanocomposite films on the structural, morphological, chemical, thermal, optical, and electrical properties of PEO/SiO₂ NPs nanocomposite films was performed. According to the x-ray diffraction and the differential scanning calorimetry analysis, the crystallinity degree of the nanocomposite films decreases by increasing the SiO₂ NPs concentrations. The bandgap energy of PEO/SiO₂ NPs nanocomposite films decreases from 3.95 to 3.55 eV as the SiO₂ NPs concentration increases up to 10 wt.%. The average electrical conductivity of the PEO/SiO₂ NPs nanocomposite films increases from 5.1 × 10⁻⁷ to 2.0 × 10⁻⁶ S/cm as the SiO₂ NPs concentration increases up to 10 wt.%. The refractive index decreases to 1.64 at 550 nm for the PEO/SiO₂ NPs nanocomposite films with 10 wt.% of SiO₂ NPs, and the water contact angle decreases to around 0° after thermal treatment, which confirms that the PEO/SiO₂ NPs nanocomposite films can be used as self-cleaning antireflected surfaces.     

Enhanced conductivity of SDC based nanocomposite electrolyte by spark plasma sintering

Recently, ceria-based nanocomposites have been considered as promising electrolyte candidates for low-temperature solid oxide fuel cells (LTSOFC) due to their dual-ion conduction and excellent performance. However, the densification of these composites remains a great concern since the relative low density of the composite electrolyte is suspected to deteriorate the durability of fuel cell. In the present study, the ionic conductivity of two kinds of SDC-based nanocomposite electrolytes processed by spark plasma sintering (SPS) method was investigated, and compared to that made by conventional cold pressing followed by sintering (normal processing way). The density of solid electrolyte can reach higher than 95% of the theoretical value after SPS processing, while the relative density of the electrolyte pellets by normal processing way can hardly approach 75%. The structure and morphology of the sintered pellets were characterized by XRD and SEM. The ionic conductivity of samples was measured by electrochemical impedance spectroscopy (EIS). The results showed that the ionic conductivity of the two kinds of electrolytes treated with SPS was significantly enhanced, compared with the electrolyte pellets processed through the conventional method. The profile of impedance curve of the electrolytes was altered as well. This study demonstrates that the conductivity of SDC based nanocomposite electrolyte can be further improved by adequate densification process.     

Magnesium and iron loaded hollow glass microspheres (HGMs) for hydrogen storage

The development of a safe and efficient method for hydrogen storage is essential for the use of hydrogen with fuel cells for vehicular applications. Hollow glass microspheres (HGMs) have characteristics suitable for hydrogen storage and are expected to be a potential hydrogen carrier to be used for energy release applications. The HGMs with 10–100 μm diameters, 100–1000 Å pore width and 3–8 μm wall thicknesses are expected to be useful for hydrogen storage. In our research we have prepared HGMs from amber glass powder of particle size 63–75 μm using flame spheroidisation method. The HGMs samples with magnesium and iron loading were also prepared to improve the heat transfer property and thereby increase the hydrogen storage capacity of the product. The feed glass powder was impregnated with calculated amount of magnesium nitrate hexahydrate salt solution to get 0.2–3.0 wt% Mg loading on HGMs. Required amount of ferrous chloride tetrahydrate solution was mixed thoroughly with the glass feed powder to prepare 0.2–2 wt% Fe loaded HGMs. Characterizations of all the HGMs samples were done using FEG-SEM, ESEM and FTIR techniques. Adsorption of hydrogen on all the Fe and Mg loaded HGMs at 10 bar pressure was conducted at room temperature and at 200 °C, for 5 h. The hydrogen adsorption capacity of Fe loaded sample was about 0.56 and 0.21 weight percent for Fe loading 0.5 and 2.0 weight percentage respectively. The magnesium loaded samples showed an increase of hydrogen adsorption from 1.23 to 2.0 weight percentage when the magnesium loading percentage was increased from 0 to 2.0. When the magnesium loading on HGMs was increased beyond 2%, formation of nano-crystals of MgO and Mg was seen on the HGMs leading to pore closure and thereby reduction in hydrogen storage capacity.