Gold-silver alloy nanoshells: a new candidate for nanotherapeutics and diagnostics

We have developed novel gold-silver alloy nanoshells as magnetic resonance imaging (MRI) dual T₁ (positive) and T₂ (negative) contrast agents as an alternative to typical gadolinium (Gd)-based contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd ions and sequestered the ions within the core by coating the nanoparticles with an alloy of gold and silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of contrast agents such as nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III) ions into the structure of the magnetite, with no major alterations of the spinel structure, as well as the growth of the gold-silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd ions within the crystalline structure with r₁ and r₂ values of 0.0119 and 0.9229 mL mg^-1 s^-1, respectively (Au:Ag alloy = 1:1). T₁- and T₂-weighted images of the nanoshells showed that these agents can both increase the surrounding water proton signals in the T₁-weighted image and reduce the signal in T₂-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the gold-silver alloy shell. Thus, these nanoshells have the potential to be utilized for tumor cell ablation because of their absorption as well as an imaging agent.     

Effects of extraction temperature, extraction pressure and nozzle diameter on micronization of cholesterol by RESS process

Micronized cholesterol particles were produced via the Rapid Expansion of Supercritical CO₂ Solutions (RESS) process. Taguchi design was used for designing the experimental plan to investigate the effects of three parameters including extraction temperature (40-60 °C), extraction pressure (100-160 bar) and nozzle diameter (0.15-0.24 mm) on the size and morphology of the cholesterol particles produced by the RESS process. The characterization of the particles was carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements to evaluate the performance of RESS process. The average particle size of the original material was 55 μm ± (2.84) while the average particle size of cholesterol after size reduction via the RESS process was between the minimum of 0.62 μm ± (0.03) and the maximum of 4.83 μm ± (0.18) depending upon the experimental conditions used. It was observed that both increasing the temperature from 40 to 60 °C and increasing the nozzle diameter from 0.15 to 0.24 mm result a reducing effect on the average particle size, whereas extraction pressure (100-160 bar) change has slight effect on the average particle size.     

Comparison of microstructure and mechanical properties of plasma-sprayed nanostructured and conventional yttria stabilized zirconia thermal barrier coatings

The main goal of this paper was to evaluate and compare the microstructure and mechanical properties of plasma-sprayed nanostructured and conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). To this end, NiCrAlY bond coat, nanostructured, and conventional YSZ coatings were deposited on Inconel 738LC substrate by atmospheric plasma spraying (APS). The mechanical properties of the coating were evaluated using nanoindentation and bonding strength tests. The microstructure and phase composition of the coating were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The nanostructured YSZ coating contained both nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of the powder, whereas the microstructure of the conventional YSZ coating consisted of columnar grain splats only. The phase composition of the as-sprayed nanostructured coating consisted of the non-transformable tetragonal phase, while the conventional coating showed the presence of both the monoclinic and non-transformable tetragonal phases. The results of nanoindentation and bonding strength tests indicated that the mechanical properties of the nanostructured coating were better than those of the conventional coating.     

Taguchi‐based analysis of polyamide 6/acrylonitrile–butadiene rubber/nanoclay nanocomposites: The role of processing variables

Applying the Taguchi method of experimental design, we prepared various polyamide 6 (PA6)/acrylonitrile butadiene rubber (NBR)/nanoclay nanocomposites under different processing conditions by melt mixing in an internal mixer. The effects of the processing variables, including the rotor speed, chamber temperature, and mixing order on the morphology, that is, the rubber particle size and interlayer distance, and the mechanical properties, that is, the tensile modulus and impact strength, were then investigated. As demonstrated with the Taguchi approach, the lower temperature associated with higher rotor speeds improved the mechanical properties of the 90/5/5 PA6/NBR/nanoclay systems. However, it was revealed that the mixing order did not affect the mechanical properties for the assigned composition. Hence, the simultaneous mixing of all the ingredients is seemingly the simplest way of mixing to obtain the desired mechanical properties. These results were confirmed with transmission and scanning electron microscopy observations and X‐ray diffraction measurements. Image analysis corresponding to the mean particle size of the NBR constituent was also performed. The optimum processing condition to achieve the appropriate mechanical properties is ultimately predicted by the Taguchi analysis and corresponded to a chamber temperature of 230°C and a screw speed of 80 rpm. Moreover, the simultaneous mixing of all of the ingredients was suggested for convenience. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 820‐828, 2013     

Modification of Theoretical models to predict mechanical behavior of PVC/NBR/organoclay nanocomposites

Organo‐modified nanoclay (Cloisite 30B) was added via direct melt mixing to the acrylonitrile butadiene rubber/poly(vinyl chloride) (PVC/NBR) to fabricate polymer blend/clay nanocomposites. The states of nano‐fillers dispersion were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). From the morphological study of nanocomposites, it is concluded that exfoliated morphology is obtainable by introduction of 2.5 vol % of nanoclay. The effect of nano‐filler volume content on the mechanical properties of PVC/NBR matrix reinforced by Cloisite 30B was investigated by tensile test. Experimental results show that the Young's modulus and tensile strength of composites can significantly improved with a small amount of nanofiller. Moreover, to investigate the stress–strain behavior of NBR/PVC nanocomposites, seven constitutive models such as Arruda–Boyce, Mooney–Rivilen, Marlow, second order of polynomial, Van der Waals, and third order Odgen were studied and compared with experimental data. Results showed that Malow and second order polynomial model can be used for nanoclay‐filled compound whereas the other models show more deviation from experimental data. Three micromechanical models named liner rule of mixtures (LROM) and the inverse rule of mixtures (IROM). Halpin–Tsai theory was applied to evaluate the dependence of Young modulus of nanocomposites on volume fraction of nanofiller. Two modifying factors were proposed to evaluate the Young's modulus of nanocomposites which could greatly improve the theoretical prediction obtained from inverse rule of mixtures (IROM) and Halpin–Tsai equation. The modifying factors were introduced by adopting an exponential, power‐law and linear factors in the equation. In order to verify the suitability of the modified models, the ensuing theoretical predictions are compared to the other experimental data available in the literature. Good predictability of the modified models is demonstrated in the results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3229–3239, 2013     

A comparative study on curing characteristics and thermomechanical properties of elastomeric nanocomposites: The effects of eggshell and calcium carbonate nanofillers

After‐hatching eggshell (AHES) nanobiofiller and nanocalcium carbonate (nano‐CA) were separately added to various elastomers, such as acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), and natural rubber (NR), in various amounts of 5, 10, and 15 phr. The effect of particle size and dispersion of such nanofillers on thermomechanical properties and curing characteristics were then investigated. The ultimate tensile properties of SBR and NR nanocomposites were improved to some extent when 5 phr of AHES nanofiller was added to the rubber compound compared to CA. In the case of NBR nanocompounds, however, the mechanical properties were seemingly comparable, irrespective of the type of nanofiller. This contradictive behavior could be attributed to the alteration of crosslink density due to particular filler–matrix interaction while using mineral and natural fillers. The results of the rheometric study revealed that using AHES rather than CA slightly increases the scorch time of all types of prepared nanocomposites, whereas a significant drop in the optimum curing time was seen for NBR nanocomposites containing AHES biofiller. Moreover, thermogravimetric analysis showed similar thermal stability for SBR nanocomposites containing AHES and CA fillers. Finer particle size of CA and higher porosity of AHES at high and low loading levels were respectively the main reasons for improvement of ultimate properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interactive Effects of Simulated Nitrogen Deposition and Altered Precipitation Patterns on Plant Allelochemical Concentrations

Global environmental change alters the supply of multiple limiting resources that regulate plant primary and secondary metabolism. Through modifications in resource availability, acquisition, and allocation, global change is likely to influence plant chemical defenses, and consequently species interactions that are mediated by these compounds. While many studies focus on individual global change factors, simultaneous changes in abiotic factors may interact to influence plant allelochemicals. In this study, we examined the individual and interactive effects of nitrogen enrichment and altered precipitation patterns on chemical defense compounds (iridoid glycosides) of an invasive plant, Linaria dalmatica. Plants were grown from seed in native mixed-grass prairie for 2 years. Nitrogen and water treatments were applied in each growing season over this period. Results indicate that soil water and nitrogen availability interact to shape plant chemical defense concentrations in L. dalmatica. Nitrogen addition decreased iridoid glycoside concentrations by approximately 25 % under reduced water availability, increased concentrations by 37 % in ambient water plots, and had no effect on these chemical defenses for plants growing under augmented water supply. Thus, results show differing patterns of allelochemical response to nitrogen enrichment, with respect to both the magnitude and direction of change, depending on water availability. Our study demonstrates the importance of examining multiple environmental factors in order to predict potential changes in plant chemical defenses with climate change.     

Application of silica gel/polyaniline composite for adsorption of ascorbic acid from aqueous solutions

Silica gel and a chemically modified silica gel with polyaniline (PAN) were used for adsorption of ascorbic acid (AA) from aqueous solutions. The surface morphology of the adsorbents was studied by scanning electron microscopy (SEM). Adsorption experiments were carried out using both batch and columnar systems. In batch system, the effects of some important parameters such as sorbent dose, contact time, initial concentration and temperature of the adsorbate were studied. Based on regression analysis, the sorption data obtained for SiO₂ were best represented by Freundlich isotherm and for the PAN/SiO₂ composite, the equilibrium sorption data were fitted better by Langmuir isotherm. The kinetic studies showed that the adsorption of AA on both sorbents follows pseudo second-order kinetics which implies a chemisorption mechanism and according to diffusion model, intra-particle diffusion is the rate-controlling step. The thermodynamic studies also showed that PAN/SiO₂ is a more effective adsorbent to adsorb AA than an unmodified SiO₂. In columnar mode, the effects of salt on breakthrough curve were investigated. Two kinetic models, Thomas and Adams–Bohart, were applied to experimental data to predict the breakthrough curves using linear regression and determine the characteristic parameters of the column. Error analysis was carried out to investigate the adequacy and accuracy of the model equations. Desorption study showed that the adsorbed ascorbic acid is readily eluted from the column using dilute solution of NaOH. PAN/SiO₂ was found to be a promising solid phase adsorbent to preconcentrate ascorbic acid from aqueous solutions and subsequent analysis.     

Fusion level optimization of rigid PVC nanocompounds by using response surface methodology

The influence of the type and content of organically modified nanoclay (NC) and the amount of calcium stearate (Ca.St) on the fusion characteristics of a poly(vinyl chloride) (PVC) nanocomposite was studied by using response surface methodology. To interpret the fusion behavior, different PVC/NC compounds were prepared in a Plasticorder with a constant rotor speed of 60 rpm while keeping the processing time and temperature constant. The results revealed that introducing NC particles into the PVC compound resulted in an increase in the maximum torque (MAT), while the minimum torque (MIT) declined. On the contrary, both the MAT and MIT values slightly increased with increasing Ca.St content. It was also found that with increasing NC content, the fusion time increased and the fusion factor decreased, whereas increasing the Ca.St lowered the fusion time. Furthermore, the difference between the MIT and MAT values demonstrated multifarious behaviors depending on the material type. Ultimately, a correlation was established between the material characteristics and the fusion factor of the PVC nanocompounds. J. VINYL ADDIT. TECHNOL., 19:168‐176, 2013. © 2013 Society of Plastics Engineers     

Nanostructure silver-doped zinc oxide films coating on glass prepared by sol–gel and photochemical deposition process: Application for removal of mercaptan

Silver-doped zinc oxide (SDZO) films have been grown on glass substrate by a novel combination of sol–gel and photochemical deposition processes (SGPD). The effect of sintering on structural, electrical and optical properties was investigated. The films were characterized by UV–vis absorption spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The result of X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of Ag 3d_5/2 for SDZO shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between silver and zinc oxide. The XRD spectra of the SDZO films indicate that silver was incorporated in the hexagonal crystal structure of zinc oxide. SEM micrographs show the uniform distribution of spherical grains of about 73 nm grain size for the pure zinc oxide thin films. The results indicated that silver doping photochemical deposition was a feasible method to tune the optical properties of zinc oxide nanostructures. SDZO films coated on glass were applied for the photodegradation of mercaptan in water. SDZO films were applied for degradation of mercaptobenzoxazole which reduced the mercaptan concentration to more than 98%.