"Click" synthesis and properties of carborane-appended large dendrimers

Large dendrimers, noted G(n)-3(n+2)cage, containing 3(n+2) o-carborane cluster cages MeC(2)B(10)H(10) at their peripheries (n = number of generation noted G(n)) have been synthesized by Huisgen-type azide alkyne Cu(I)-catalyzed dipolar "click" cycloaddition reactions (CuAAC) between an o-carborane monomeric cluster containing an ethynyl group and arene-centered azido-terminated dendrimers G(n)-3(n+2)N(3) of generations 0, 1, and 2. Attempts to synthesize higher-generation dendrimers of this family yielded insoluble materials. The carborane dendrimers G(0)-9cage, G(1)-27cage, and G(2)-81cage have been characterized by (1)H, (13)C, (11)B NMR, elemental analysis, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectroscopy, and size exclusion chromatography (SEC) showing low polydispersities, dynamic light scattering (DLS) showing hydrodynamic diameters of 5.7 nm for the G(1)-27cage and the 12.9 nm for the G(2)-81cage. These dendrimers are extremely robust thermally, with 10% mass loss temperatures of 411 °C for the G(0)-9cage, 371 °C for the G(1)-27cage, and 392 °C for the G(2)-81cage. They all showed a strong absorption in the UV region peaking at 258 nm, whereas emission spectra of low intensities were observed between 280 and 480 nm.     

Initial stages of MnAs/GaAs(0 0 1) epitaxy studied by RHEED azimuthal scans

We study the nucleation phase of molecular beam epitaxy of (hexagonal) MnAs on (cubic) GaAs (0 0 1) using reflection high-energy electron diffraction (RHEED) azimuthal scans. The nucleation proceeds from a non-reconstructed initial stage through randomly oriented small nuclei and two orientation stages to the final single-phase epitaxial orientation. The fascinatingly complex nucleation process contains elements of both Volmer-Weber and Stranski-Krastanov growth. The measurement demonstrates the potential of high-resolution RHEED techniques to assess details of the surface structure during epitaxy.     

Prediction and simulation of wear response of Linz–Donawitz (LD) slag filled glass–epoxy composites using neural computation

This article reports on the implementation of a soft computing technique based on artificial neural networks (ANNs) in analyzing the wear performance of a new class of hybrid composites filled with Linz–Donawitz slag (LDS). LDS is a major solid waste generated in huge quantities during steel making. It comes from slag formers such as burned lime/dolomite and from oxidizing of silica, iron etc. while refining the iron into steel in the LD furnace. In this work, hybrid composites consisting of short glass fiber (SGF) reinforced epoxy filled with different LDS content (0, 7.5, 15 and 22.5 wt%) are prepared by simple hand lay‐up technique. Solid particle erosion trials, as per ASTM G 76 test standards, are conducted on the composite samples following a well‐planned experimental schedule based on Taguchi design of experiments. Significant process parameters predominantly influencing the rate of erosion are identified. The study reveals that the LDS content is the most significant among various factors influencing the wear rate of these composites. Further, a model based on ANN for the prediction of erosion performance of these composites is implemented. The ANN prediction profiles for the characteristic wear properties exhibit very good agreement with the measured results demonstrating that a well‐trained network has been created. The simulated results explaining the effect of significant process variables on the wear rate indicate that the trained neural network possesses enough generalization capability of predicting wear rate even beyond the experimental range. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of chain architecture on phase behaviour of styrene-(styrene/butadiene)-styrene triblock copolymers and their binary blends

The phase behaviour of symmetric (LN4) and asymmetric (LN3) triblock copolymers based on styrene-b-(styrene-co-butadiene)-b-styrene (S-SB-S) and their blends have been studied using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) and were correlated with rheological properties. A direct control over the final morphology and segregation strength for the block copolymer blends was achieved by blending of LN3 and LN4. The interaction parameter (χ) for LN4 is extracted by fitting the SAXS patterns at temperatures well above the ODT in consistency with Leibler mean-field structure-function for ABA triblock copolymers. A weak temperature dependency of χ has been observed which revealed that the phase behaviour in LN4 is mainly controlled by the entropic term. In the low frequency regime a non-terminal flow behaviour was observed in LN3 revealing the persistence of ordered structure within the experimental temperature range whereas a terminal flow behaviour with composition fluctuation was observed in LN4. G′ vs. G″ plots indicated a solid-like elastic melt behaviour for LN3 whereas presence of ODT over a broad temperature range was observed for LN4. ODT is observed to increase non-linearly with increase in LN3 content in the blends. ODT behaviour of the blends further reveals that the blends shift from weak-segregation to intermediate-segregation strength with the increase in LN3 content. The improvement in the state of ordering along with the change in morphology with the increase of LN3 content is attributed to co-surfactant effect between the PS end-blocks of LN3 and LN4 inside PS-rich phase.     

Kalman particle swarm optimized polynomials for data classification

Data classification is an important area of data mining. Several well known techniques such as decision tree, neural network, etc. are available for this task. In this paper we propose a Kalman particle swarm optimized (KPSO) polynomial equation for classification for several well known data sets. Our proposed method is derived from some of the findings of the valuable information like number of terms, number and combination of features in each term, degree of the polynomial equation etc. of our earlier work on data classification using polynomial neural network. The KPSO optimizes these polynomial equations with a faster convergence speed unlike PSO. The polynomial equation that gives the best performance is considered as the model for classification. Our simulation result shows that the proposed approach is able to give competitive classification accuracy compared to PNN in many datasets.     

Synthesis and Characterization of Reversible Chemosensory Polymers: Modulation of Sensitivity through the Attachment of Novel Imidazole Pendants

Three novel electron donor–acceptor conjugated polymers ( P1 – P3 ) bearing various imidazole pendants have been synthesized. Their excellent photophysical and electrochemical properties make them suitable transduction materials for chemosensing applications. Indeed, polymers P1 – P3 have been found to show remarkable sensing capabilities towards H⁺ and Fe²⁺ in semi‐aqueous solutions. Upon titration with H⁺, polymers P1 and P2 showed hypsochromic shifts of their absorptions and photoluminescence (PL) maxima with enhanced fluorescence intensities. However, P3 showed diminished absorption and fluorescence intensities under similar conditions due to static quenching. The anomalous behavior of P3 compared with P1 and P2 has been clarified in terms of electronic distributions through computational analysis. Furthermore, P3 (K_SV=1.03×10⁷) showed a superior sensing ability towards Fe²⁺ compared with P1 (K_SV=2.01×10⁶) and P2 (K_SV=4.12×10⁶) due to its improved molecular wire effect. Correspondingly, the fluorescence lifetime of P3 was greatly decreased (almost 11‐fold) compared to those of polymers P1 (4.6‐fold) and P2 (6.2‐fold) in the presence of Fe²⁺. By means of a fluorescence on‐off‐on approach, chemosensing reversibilities in protonation–deprotonation and metallation–demetallation have been achieved by employing triethylamine (TEA) and the disodium salt of ethylenediaminetetraacetic acid (Na₂‐EDTA)/phenanthroline, respectively, as suitable counter ligands. ¹H NMR titrations have revealed the unique behavior of P3 compared with P1 and P2 . To the best of our knowledge, there have been no previous reports of Fe²⁺ sensors based on single imidazole receptors conjugated to a main‐chain polymer showing such a diverse sensitivity pattern depending on their attached substituents.     

Crack Toughness Behaviour of Multiwalled Carbon Nanotube (MWNT)/Polycarbonate Nanocomposites

Summary: The morphology and fracture behaviour of polycarbonate (PC)/multiwalled carbon nanotube (MWNT) composites have been studied by AFM and post‐yield fracture mechanics. The essential work of fracture (EWF) method has been used to distinguish between two terms representing the resistance to crack initiation and crack propagation. A maximum in the non‐essential work of fracture was observed at 2 wt.‐% MWNT, demonstrating enhanced resistance to crack propagation compared to pure PC. At 4 wt.‐% MWNT, a tough‐to‐brittle transition has been observed. The time‐resolved in‐situ strain field analysis revealed that the onset of crack initiation was shifted to a shorter time for nanocomposites with 4 wt.‐% MWNT compared to that with 2 wt.‐%, and thus explained the existence of a tough‐to‐brittle transition in these nanocomposites.

     

Dynamic mechanical and rheological properties of binary S–(S/B)–S triblock copolymer blends

The rheology and dynamic mechanical properties of binary block copolymer blends consisting of a symmetrical triblock copolymer with thermoplastic elastomeric behavior (LN4) and an asymmetrical thermoplastic triblock copolymer (LN3) were investigated. TEM images of the blends show a systematic variation in the morphologies from worms (～20–0 wt % LN3) to cylinders (～60–30 wt % LN3) to lamellae (100–70 wt % LN3) as a function of LN3 content. DMA analysis has revealed that the increase in LN3 content leads to a decrease in miscibility between the PS end blocks and the S/B middle block. The frequency and temperature dependence of the storage modulus (G′), loss modulus (G″), and complex viscosity (|η*|) has been studied for LN4 (weakly segregated) and LN3 (strongly segregated) from their master curves. By comparing the rheological properties of these blend compositions at low‐frequency regime, it is observed that with the increase in LN3 content the shear modulus and complex viscosity increase. Blend compositions with 70–100 wt % of LN3 show nonterminal behavior at reduced frequencies due to the presence of highly ordered microdomains when compared to blends with ～0–20 wt % of LN3 content. van Gurp–Palmen plots were constructed to observe the transition from liquid‐ to solid‐like behavior in the vicinity of order‐to‐disorder transition (ODT) temperature. ODT temperature increases as the thermoplastic LN3 content increases which are also confirmed by the Han plots. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 329–343, 2008     

Biomimetic oxidation of N-nitrosodibenzylamine with molecular oxygen catalysed by chemical cytochrome P-450 in AOT reverse micelles

Moderate yields of benzaldehyde, benzyl alcohol and benzylamine are obtained by the biomimetic oxidation of N-nitrosodibenzylamine with molecular oxygen catalysed by water soluble anionic manganese(III) 5,10,15,20-tetraphenylporphyrin acetate/sodium dithionite/methylene blue in aerosol-OT (AOT) reverse micelles, under phase transfer conditions with AOT concentration higher than 10⁻³M. The formation of α-hydroxy-N-nitrosodibenzylamine and its decomposition products, benzaldehyde and benzyl alcohol in reverse micellar systems are governed by the ratio of water and AOT, pH and other changes in the microenvirpnment.