Epitaxial nucleation model for chiral-selective growth of single-walled carbon nanotubes on bimetallic catalyst surfaces

An epitaxial nucleation model for single-walled carbon nanotube (SWCNT) growth on bimetallic catalysts surfaces is reported in support of experimental observations of chiral enrichment. We model the bimetallic catalyst surfaces as a 2D (1 1 1) surface consisting of Ni or a combination of Ni and Fe atoms, with varying average bond length between nearest neighbor atoms which corresponds to the crystal structure of the alloys. The energies associated with nanotube cap formation on these various surfaces are calculated using density functional theory (DFT). We find that certain cap chiralities, such as (8, 4), are more stably bound to a surface that resembles a Ni_0.27Fe_0.73 bimetallic catalyst, whereas other chiralities, such as (9, 4), are more stable on a pure Ni surface. These results help explain the predominance of certain chiralities on specific bimetallic catalysts and provide a potential route to controlling the chirality of as-grown SWCNTs.     

Solubility parameter estimation and phase inversion modeling of bentonite-doped polymeric membrane systems

Effects of bentonite concentration on morphology and permeation characteristics of bentonite-doped polysulfone membranes were investigated. Solubility sphere for bentonite was constructed to estimate its solubility parameter. Thermodynamic modeling of phase inversion of this system was carried out using Flory–Huggins theory. The trade-off between thermodynamic and kinetic parameters was used to predict the membrane morphology for bentonite concentration varying from 0 to 5 wt %. The porosity of bentonite-doped membranes decreased up to 3 wt % that increased thereafter. Morphological analysis showed dense cross section with finger-like macrovoids at 3 wt % beyond which it changed to honeycomb structure with large circular voids. Permeability of 3 wt % membrane was the lowest (5.6 × 10⁻¹² m/Pa s) with 95% bovine serum albumin rejection. Contact angle of the membranes decreased from 83 to 66° with bentonite addition making the membrane more hydrophilic. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48450.     

Benzene physical and chemical organogels: Effect of network scaffolding on the thermodynamic behavior of entrapped solvent molecules

This paper presents a thermodynamic investigation of the benzene physical and chemical organogels, using differential scanning calorimetry (DSC) and intends to draw an appropriate relationship between the gel network structure and the properties. Physical gels, formed by an aluminium soap of fatty acid, and chemical gels, created by in situ cross‐linking of a siloxane copolymer are investigated. The effects of the type and quantity of the gelators and their corresponding network mesh size distribution in the gels on crystallization, melting, and their kinetics are examined. It appears that the kinetics of crystallization of the entrapped solvent is significantly affected by the quality of the gel network scaffolding and can be treated successfully by the Avrami equation of crystallization. From the melting behavior of the entrapped solvent crystallites, quantitative information about the number of solvent molecules bound per molecule of the gelator has been extracted. DSC proves to be a reliable technique to evaluate the population distribution of solvent molecules trapped in the physical and chemical organogel network scaffolding. The state of the solvent may be treated as a probe to understand the structure of the gels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1253–1264, 2004     

Loading rate sensitivity of liquid nitrogen conditioned glass fiber reinforced polymeric composites: An emphasis on tensile and thermal responses

Glass fiber reinforced polymeric (GFRP) composites are being accepted as potential materials for ultra‐low temperature applications. The current investigation is to evaluate effect of liquid nitrogen (LN₂) conditioning (for different intervals of time) on the loading rate sensitivity of tensile response of GFRP composites. In order to assess this, tensile tests of the unconditioned and conditioned specimens were carried out at different crosshead speeds viz. 1, 10, 100, 500, and 1000 mm/min. At 1 mm/min crosshead speed, an improvement of 3.33% and 7.3% ultimate tensile strength (UTS) value was observed in case of 0.25 and 1 h conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Similarly, the specimens tested at 1000 mm/min show an improvement of 11.39% and 12.02% UTS for 0.25 and 1 h LN₂ conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Effect of LN₂ conditioning on crosshead speed sensitivity of modulus and strain at break are also reported. The in‐service temperature of the GFRP composite was measured using temperature modulated differential scanning calorimetry. Furthermore, dynamic mechanical thermal analyzer was used in the temperature range (40–200 °C) to correlate the mechanical and thermomechanical response of the GFRP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45856.     

Influence of thermal and morphological characteristics on mechanical responses of polypropylene/γ‐irradiated elastomer blends

The approach of this paper is to examine the mechanical responses of polypropylene (PP)/γ‐irradiated ethylene acrylic elastomer blends and subsequently compare them with the PP/unirradiated ethylene acrylic elastomer blends. Thorough correlations were drawn between the mechanical characteristics of blends and their morphological, thermal, thermomechanical, and fractured surface morphological aspects. The idea of carrying out γ‐irradiation was to introduce crosslinking points in the elastomer phase. For better understanding, correlations between the impact test results and the fractured surface morphologies were analyzed. The limited tensile properties of PP/γ‐irradiated elastomer blends were attributed not only to the poor interfacial adhesion, obtained by fitting with several theoretical mechanical models, but also to the substantially higher elastomer particle size in the blends than in the PP/unirradiated elastomer blends. The higher loss modulus and tan δ values for PP/unirradiated elastomer blends along with the attainment of much smaller particles of elastomers were responsible for the phenomenal increase in impact properties, which was actually attributed to the formation of crazes inside the dispersed phase during applied impact stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46597.     

Phase Transformation of Metastable ZnSnO3 Upon Thermal Decomposition by In‐Situ Temperature‐Dependent Raman Spectroscopy

Temperature‐dependent in‐situ Raman spectroscopy is used to investigate the phase transformation of zinc metastannate (ZnSnO₃) to zinc orthostannate (Zn₂SnO₄) induced upon annealing in the ambient. ZnSnO₃ microcubes (MCs) were synthesized at room temperature using a simple aqueous synthesis process, followed by characterization using electron microscopy, X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). Annealing of the ZnSnO₃ MCs was carried out up to 1000°C, while recording the Raman spectra in‐situ at regular intervals. Phase transformation from metastannate to orthostannate was found to begin around 500°C with an activation energy of ~0.965 eV followed by the recrystallization into the inverse spinel orthostannate phase at ~750°C. Results from this study provide detailed understanding of the phase transformation behavior of perovskite ZnSnO₃ to inverse spinel Zn₂SnO₄ upon thermal annealing.     

Effect of co‐solvents on the photovoltaic performance of an inverted organic solar cell

We investigated the effect of varying polymer crystallinity, morphology, and optical property, produced by adding four different co‐solvents in to the poly(3‐hexylthiophene) (P3HT): [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) active layer blend solution, on the functioning of an inverted polymeric solar device. Photovoltaic devices primed with cyclohexanone co‐solvent showed the best performance with power conversion efficiency (PCE) reaching a value of 3.01 ± 0.04%. Improvement in efficiency is related to an increase in photocurrent which is due to a combined result of ordered P3HT crystallite growth, as well as of the precise size and phase separation of domains. POLYM. ENG. SCI., 55:1382–1388, 2015. © 2015 Society of Plastics Engineers     

Studies on phytosterol oxides. II: Content in some vegetable oils and in French fries prepared in these oils

Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time. Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX.     

Melt Rheological Behavior and Creep Response of EVA/TPU Blends: Exploring the Effect of Electron Beam Irradiation and Peroxide Cross-linking

The present study focuses on the variation of the melt rheological characteristics and the creep behavior of both electron beam-cross-linked and peroxide-cured ethylene vinyl acetate/thermoplastic polyurethane blends. The variation of complex viscosity, complex modulus, storage modulus, and loss modulus was evaluated over a wide range of frequency and strain amplitude using rubber process analyzer and the effect of radiation dose and peroxide concentration was investigated in detail. The creep study using dynamic mechanical analyzer shows that the creep behavior of the blends significantly improves after cross-linking and the creep compliance gradually decreases with the increasing radiation dose and peroxide content. An attempt was also made to pursue a comparative rheological and creep study among the peroxide-cured, electron beam-cross-linked and the coagent-treated dynamically vulcanized samples.     

Synthesis and characterization of solid-phase super acid catalysts and their application for isomerization of n-alkanes

In the present work, first, the reference catalyst super acidic nanostructured sulfated zirconia (SZ) and super acidic nanostructured aluminum chloride impregnated sulfated zirconium oxides in mole ratios of Zr⁴⁺:Al³⁺ as 2:1 (ACSZ-1), 1:1 (ACSZ-2), and 1:2 (ACSZ-3) were synthesized by a simple precipitation method. The catalytic performance of these four catalysts were evaluated during the isomerization of n-hexane, n-heptane, and n-octane to their corresponding branched chain isomers at low temperature and pressure conditions. ACSZ-2 shows high activity toward isomerization of n-hexane, n-heptane, and n-octane into their corresponding branched chain isomers. The reference catalyst SZ was proved to be less effective compare to the other three synthesized ACSZ catalysts. Ammonia-temperature-programmed desorption of these two materials ensures that the super acidity of ACSZ-2 is higher than that of SZ. Atomic force microscopic and scanning electron microscopic pictures predict the nature of the surface of the catalysts. Transmission electron micrographic analysis indicates the presence of particle-bulks having average size 12–20?nm, presenting an amorphous nature and having no definite surface morphology of ACSZ-2. Fourier transform infrared provides an outline regarding different linkages and bond connectivities between atoms and groups in ACSZ-2 and SZ. After catalyst evaluation and characterization a probable reaction mechanism has been proposed theoretically. The reactivity and selectivity of ACSZ-2 and SZ as well as the order and activation energy of the isomerization reactions in presence of ACSZ-2 have been calculated. The use of ACSZ-2 is beneficial from the point of cost efficiency as well as its use is energy saving.