Polypropylene random copolymer/MWCNT nanocomposites: Isothermal crystallization kinetics,structural, and morphological interpretations

This article describes the crystallization process of polypropylene random copolymer (PPCP) under isothermal conditions in presence of varying amounts of multiwalled carbon nanotubes (MWCNT) ranging from 0.5 to 4.0% w/w. Increase in the crystallization temperature under dynamic conditions confirmed the nucleating behavior of MWCNTs, which was also corroborated by crystallization studies under isothermal conditions. The crystallization kinetics was analyzed using Avrami equation and the parameters such as Avrami exponent, the equilibrium melting temperature and fold surface energy for the crystallization of PPCP chains in nanocomposites were obtained from the calorimetric data in order to determine the effect of MWCNTs on these parameters. Spherulitic growth of PPCP crystals was also investigated as a function of time and MWCNT content using hot stage polarizing microscope. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41734.     

Iodine‐Mediated Copper‐Catalyzed Efficient α‐C(sp2)‐Thiomethylation of α‐Oxoketene Dithioacetals with Dimethyl Sulfoxide in One Pot

The direct α‐Csp² H functionalization and thiomethylation of α‐oxoketene dithioacetals (DTAs) has been accomplished with dimethyl sulfoxide (DMSO) in the presence of iodine and a copper(I) salt for the first time. A prerequisite is the in situ iodination of the α‐Csp² atom of dithioacetals that could offer other reaction channels. The operationally simple one‐pot protocol includes region‐defined consecutive iodination and sulfenylation of the challenging α‐Csp² H bond of dithioacetals employing cheap and readily available reagents. DMSO here plays a dual role as thiomethyl source and solvent.

     

Ammonia Decomposition on Ir(100): From Ultrahigh Vacuum to Elevated Pressures

Ammonia decomposition on Ir(100) has been studied over the pressure range from ultrahigh vacuum to 1.5 Torr and at temperatures ranging from 200 to 800 K. The kinetics of the ammonia decomposition reaction was monitored by total pressure change. The apparent activation energy obtained in this study (84 kJ/mol) is in excellent agreement with our previous studies using supported Ir catalysts (Ir/Al₂O₃ 82 kJ/mol). Partial pressure dependence studies of the reaction rate yielded a positive order (0.9±0.1) with respect to ammonia and negative order (–0.7 ±0.1) with respect to hydrogen. Temperature-programmed desorption data from clean and hydrogen co-adsorbed Ir(100) surfaces indicate that ammonia undergoes facile decomposition on both these surfaces. Recombinative desorption of N₂ is the rate-determining step with a desorption activation energy of 63 kJ/mol. Co-adsorption data also indicate that the observed negative order with respect to hydrogen pressure is due to enhancement of the reverse reaction (NH _x + H NH _x+1, x=0–2) in the presence of excess H atoms on the surface.     

Safe design fatigue life of CNT loaded woven GFRP laminates under fully reversible axial fatigue: application of two-parameters Weibull distribution

ABSTRACT

In this work, constant amplitude fully reversible tension-compression (t-c) fatigue behaviour of two-phased epoxy/glass fibre and three-phased MWCNT/epoxy/glass fibre laminates modified with 0.5 and 1.0 vol.-% of MWCNTs is presented. Addition of 0.5 and 1.0 volume fraction of nanoparticles in the matrix phase increased the fatigue strength of the laminates by approximately 10% and 4%, respectively. GFRP laminates subjected to quasi-static compression and t-c fatigue were found to fail by matrix crushing and shearing contrary to matrix crushing, ply splitting and kink band failure presented by CNT modified laminates. Such mechanisms were due to additional matrix toughening imparted by the nanotubes. Two-parameters Weibull distribution was implemented for the statistical evaluation of the fatigue life data. For safety limits of the test results, S-N curves with reliability levels of 0.99, 0.5, 0.368 and 0.10 were produced using Weibull shape and scale parameters.     

Surfactant-catalyzed SiO2 thin films preparation and characterization

SiO₂ thin films are in high demand for wide range of applications including microelectronics, optoelectronics, solar energy conversion, photocatalysis, and self-cleaning coatings. The performance of thin film is strongly influenced by surface properties like surface roughness, thickness, morphology, wetting behavior, and thermal stability. In these applications, the SiO₂ sols were prepared using tetraethylorthosilicate as a source of SiO₂ and deposited on 100?×?40?×?2?mm³ glass slide using dip-coating method for 2?min and calcined at 250?°C for 30?min. The SiO₂ thin films were obtained using DTAB, SDS, and Tween 20 (Tw 20) surfactants with the thickness of 36.92, 47.15, and 52.39?nm, respectively. Surface morphology was studied with AFM and surface roughness was depicted with 0.9528, 3.6534, and 0.9294?nm. Contact angle measurements have been performed with goniometer to evaluate the wetting behavior of the film. The contact angle of 58.01°, 48.40°, and 37.88° was observed with SDS, DTAB, and Tw 20 film, respectively. The SiO₂ thin films with SDS showed more surface roughness and water repelling ability when compared to DTAB and least with Tw 20.     

Effect of isomerization on thermal behaviour of bisitaconimides

The effect of isomerization of N,N′‐bisitaconimido‐4,4′‐diphenyl ether to the corresponding biscitraconimide on the curing characteristics and thermal stability of cured resins is described. Resins having bisitaconimide:biscitraconimide ratios of 23:77–93:7 were prepared by reacting 4,4′‐diaminodiphenyl ether with itaconic anhydride in solvents of different polarities and under different reaction conditions. Resins containing a higher proportion of citraconimide had a lower melting point (191 vs 208 °C). The curing exotherm was observed immediately after melting in all the resins and exothermic peak temperature reduced with increase in citraconimide content. Resins having a higher proportion of citraconimide on isothermal curing (200 °C, 2 h) and subsequent heating in nitrogen atmosphere degraded at a slightly lower temperature. However, the char yield at 800 °C did not show any systematic dependence on citraconimide content. © 2002 Society of Chemical Industry     

Non-fluorinated hybrid composite membranes based on polyethylene glycol functionalized polyhedral oligomeric silsesquioxane [PPOSS] and sulfonated poly(ether ether ketone) [SPEEK] for fuel cell applications

Novel hybrid composite membranes were prepared by blending poly(ethylene glycol) functionalized polyhedral oligomeric silsesquioxane [PPOSS] as nanofiller in varying concentration ranging from 1 to 5% (w/w) into sulfonated poly(ether ether ketone) [SPEEK] with degree of sulfonation ～55% for proton exchange membrane fuel cells [PEMFCs]. The effect of incorporation of PPOSS into SPEEK matrix was investigated in terms of thermomechanical and morphological properties, water uptake and proton conductivity of SPEEK. All the composite membranes were thermally and mechanically stable up to 250 °C. Transmission electron microscopy (TEM) revealed that the smallest particle size (～100 nm) of PPOSS was found for SPEEK membranes containing 2% (w/w) PPOSS where as agglomeration (～300 nm) was observed at higher loadings of PPOSS. The proton conductivity was found to be dependent on the morphology and was independent of the amount of water present in the membranes. At 100 °C and 100% RH, the highest proton conductivity (47 mS/cm compared 34 mS/cm for neat SPEEK i.e. an increase of ～51%) was recorded at 2% (w/w) PPOSS contents followed by a decrease on further addition of PPOSS.The water uptake of composite membranes increased with concentration of PPOSS while maintaining their hydrolytic stability at 100 °C for more than 24 h.     

The Organization of the Quorum Sensing luxI/R Family Genes in Burkholderia

Members of the Burkholderia genus of Proteobacteria are capable of living freely in the environment and can also colonize human, animal and plant hosts. Certain members are considered to be clinically important from both medical and veterinary perspectives and furthermore may be important modulators of the rhizosphere. Quorum sensing via N-acyl homoserine lactone signals (AHL QS) is present in almost all Burkholderia species and is thought to play important roles in lifestyle changes such as colonization and niche invasion. Here we present a census of AHL QS genes retrieved from public databases and indicate that the local arrangement (topology) of QS genes, their location within chromosomes and their gene neighborhoods show characteristic patterns that differ between the known Burkholderia clades. In sequence phylogenies, AHL QS genes seem to cluster according to the local gene topology rather than according to the species, which suggests that the basic topology types were present prior to the appearance of current Burkholderia species. The data are available at http://net.icgeb.org/burkholderia/.     

Texture modeling in carbon-carbon composites based on mesophase precursor matrices

A computational modeling study of texture formation in carbon-carbon composites based on carbon fibers and carbonaceous mesophase precursors is presented. The modeling predictions on texture formation and disclination structures are quantitatively validated with extensive experimental data. The number and type of disclinations displayed by the carbonaceous mesophase matrix is shown to be governed by the elasticity of the mesophase, the carbon fiber-mesophase interfacial energy, the size of the fibers, and positional arrangement of the fibers. The simulations provide new insights on the fundamental principles that govern texturing and disclination nucleation, and on how to control the structure of carbon-carbon composites through fiber concentration, fiber cross-section, and fiber-matrix interaction.     

Geometrical Variability Impact on the Performance of Sub - 3 nm Gate-All-Around Stacked Nanosheet FET

Silicon - To meet the scaling targets and continue with Moore’s Law, the transition from FinFET to Gate-All-Around (GAA) nanosheet Field Effect Transistors (FETs) is the necessity for...