Achieving structural control with thin polystyrene-b-polydimethylsiloxane block copolymer films: The complex relationship of interface chemistry,annealing methodology and process conditions

The structure of thin microphase-separated polystyrene-block-polydimethylsiloxane (PS–PDMS) films has been studied using state-of-the-art top-down and cross-sectional electron microscopy. This is the first time that the profile of PS–PDMS films has been measured in situ and these measurements allowed us to image the shape of the PDMS domains within the film as well as examine the wetting behavior of the block copolymer film on a variety of substrates. It was found that for each polymer, substrate chemistry and annealing method combination examined, there was a small range of film thicknesses whereby the films exhibited the optimal characteristics of high levels of ordering without dewetting or multilayering. Specifically, the optimum thickness for films treated by thermal annealing was greater than that for the equivalent solvent annealed film; a change that was correlated with morphology variations related to solvent swelling of the solvent annealed films. The surface chemistry also induced changes in the optimum film thickness. Selective surfaces were shown to control whether a PDMS wetting layer was formed or not, leading to either thicker or thinner wetting optimum film thicknesses; while undulating morphologies were observed for less selective surfaces. Concomitant changes in the periodicity were then hypothesized to occur as a result of confinement effects and the selectivity of the surface.     

P2O5/SiO2 as an Efficient Reagent for Selective Deprotection of 1,1‐Diacetates under Solvent‐Free Conditions

A mild and efficient method has been developed for the selective deprotection of 1,1‐diacetates of aldehydes in excellent yields by means of the P₂O₅/SiO₂ reagent. Advantages of this method are the use of inexpensive and selective reagent, with high yields in simple operation, and short reaction time under solvent‐free conditions.     

Green biosynthesis of silver nanoparticles using Callicarpa maingayi stem bark extraction

Different biological methods are gaining recognition for the production of silver nanoparticles (Ag-NPs) due to their multiple applications. The use of plants in the green synthesis of nanoparticles emerges as a cost effective and eco-friendly approach. In this study the green biosynthesis of silver nanoparticles using Callicarpa maingayi stem bark extract has been reported. Characterizations of nanoparticles were done using different methods, which include; ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDXF) spectrometry, zeta potential measurements and Fourier transform infrared (FT-IR) spectroscopy. UV-visible spectrum of the aqueous medium containing silver nanoparticles showed absorption peak at around 456 nm. The TEM study showed that mean diameter and standard deviation for the formation of silver nanoparticles were 12.40 ± 3.27 nm. The XRD study showed that the particles are crystalline in nature, with a face centered cubic (fcc) structure. The most needed outcome of this work will be the development of value added products from Callicarpa maingayi for biomedical and nanotechnology based industries.     

Effect of hydrophilicity of room temperature ionic liquids on the electrochemical and electrocatalytic behaviour of choline oxidase

In the present report, six different nano-composites contaning the same amine functionalized multi-walled carbon nanotubes (NH(2)-MWCNTs) but different room temperature ionic liquids (RTILs) were prepared. Then, the efficiency of these nano-composites as supporting materials for studying the electrochemistry and electrocatalysis of choline oxidase (ChOx) as a model enzyme were compared. The corresponding cyclic voltammetric and amperometric data showed that the electrocatalytic activity and the electroanalytical performance of immobilized ChOx depends on the degree of hydrophilicity of RTILs used in the applied nano-composite. The higher stability (180 days), higher enzyme loading (6.56 mol cm(-2)), lower detection limit (3.85 μM) and wider linear range (0.005-0.8 mM) was obtained for the most hydrophilic RTIL (1-allyl-3-methylimidazolium bromide).     

Single-shot distributed optical-fiber temperature sensing by the frequency-derived technique

We present, for the first time to our knowledge, a distributed optical-fiber temperature sensor, based on a pulsed laser, that provides distributed temperature measurement by use of a single pulse propagating in an optical fiber. The system uses the frequency-derived technique based on the optical Kerr effect. The performance of the system is investigated for the temperature range 33-150 degrees C. A linear relationship between the temperature and the derived frequency is obtained. The best temperature resolution was determined to be +/-1.2 degrees C. The best measured spatial resolution was 0.56 m.     

Investigation of vacancy defects effects on the buckling behavior of SWCNTs via a structural mechanics approach

In this paper, the influence of various vacancy defects on the critical buckling loads and strains in carbon nanotubes under axial compression is investigated via a new structural model in ABAQUS software. The necessity of desirable conditions and expensive tests for experimental methods, in addition to the time expenditure required for atomic simulations, are the motivation for this work, which, in addition to yielding accurate results, avoids the obstacles of the previous methods. In fact, this model is a combination of other structural models designed to eliminate the deficiencies inherent in individual approaches. Because the present model is constructed in the CAE space of ABAQUS, there is no need to program for different loading and boundary conditions. A nonlinear connector is considered for modeling of stretching and torsional interactions, and a nonlinear spring is used for modeling of the angle variation interactions. A Morse potential is employed for stretching and bending potentials, and a periodic type of bond torsion is used for torsion interactions. The effect of different types of vacancy defects at various locations on the critical buckling loads and strains is studied for zigzag and armchair nanotubes with various aspect ratios (Length/Diameter). Comparison of our results with those of buckling of shells with cutouts indicates that vacancy defects in the carbon nanotubes can most likely be modeled as cutouts of the shells. Finally, results of the present structural model are compared with those from molecular dynamics (MD) simulation and show good agreement between our model and the MD model.     

Hollow nanoshell-sphere Fe@Fe/Pd reactors: a magnetically recoverable catalyst for the C<Subscript>sp</Subscript>–S cross-coupling reactions in water

The hollow Pd–PVP–Fe nanosphere and Fe–PVP nanoparticle catalysts were synthesized by thermal method. Mixing of two metallic nanocatalysts was applied in the C_sp–S cross-coupling reactions between diphenyl disulfide and phenylacetylene under mild conditions in water. Results show that bi-catalytic system has higher catalytic efficiencies than their monocatalytic systems due to synergy between two catalysts. Order of adding two metallic catalysts were adjusted into the coupling reaction medium. Therefore, various bi-catalytic systems were obtained and characterized by XRD, SEM, EBSD, EDX, UV–Vis spectra, and particle size analyzer. Under special order of adding, the obtained hollow nanoshell-sphere Fe@Fe/Pd reactor showed higher catalytic activity in the coupling reaction compared to other bi-catalytic systems. The C_sp–S coupling products obtained of various diaryl disulfides and phenylacetylene at presence Fe@Fe/Pd (only 7.3?×?10^?5 mmol Pd) catalyst with moderate to high yields in water solvent and mild reaction conditions. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The recovered catalyst was characterized by XRD, SEM, EBSD, EDX, and UV–Vis spectra. The Fe@Fe/Pd was reused at least six repeating cycles without any loss of its high catalytic activity. Tuning morphology and chemical composition of bi-catalytic system are key mainstays of high activity of Fe@Fe/Pd in repeating cycles of cross-coupling reactions.     

Superoxide radical biosensor based on a nano-composite containing cytochrome c

A biosensor for the quantification of superoxide radical (O(2)˙(-)) was developed based on a nano-composite containing cytochrome c (Cyt c), carboxylated multi-walled carbon nanotubes and a room temperature ionic liquid (RTIL). The immobilized Cyt c was characterized by field emission scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Using this biosensor a formal potential of -280 mV (vs. Ag/AgCl) and electron transfer rate constant of 1.24 was recorded for the immobilized Cyt c in 0.1 M phosphate buffer solution (pH 7.0). The biosensor showed a relatively high sensitivity (7.455 A M(-1) cm(-2)) and a long term stability (180 days) towards O(2)˙(-) in the concentration range from 0.05 to 8.1 μM with a detection limit of 0.03 μM. The selectivity of the biosensor to O(2)˙(-) was verified when its response was compared with those obtained by four potential interfering substances (ascorbic acid, uric acid, acetaminophen and hydrogen peroxide).