Synthesis and characterization of APTMS/melamine cured hyperbranched polyester-epoxy hybrid coatings

An epoxy-terminated hyperbranched polyester (EPHBP) was prepared by the reaction of hyperbranched polyester (HBP) and epichlorohydrin (EPH). Herein, we have synthesized a new kind of highly epoxy ended branched polyester to enhance the chemical bonding at the interfaces and to reduce the melt viscosity. The structural investigation of the hyperbranched polyesters was carried by spectroscopic techniques such as nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) while molar masses were determined using gel permeation chromatography (GPC). The effect of the content of hexamethoxy methyl melamine (HMMA) and 3-amino propyltrimethoxysilane (APTMS) mixture on the thermal, mechanical and interfacial properties of EPHBP resins were also studied. The thermal, dynamic mechanical and mechanical properties of the heat cured coating films were also investigated. The combined analysis of the results indicate that the introduction of APTMS results in the enhancement of the thermal stability, glass-transition temperature (T_g), storage modulus, tensile strength and contact angle of the cured films. The improvement in properties depends on the APTMS content of the cured films. The cured films have also shown higher elongation at break due to the use of HMMA and presence of unmodified epoxide groups which indicates good flexibility and toughness of the coating films.     

Similarity solutions for laminar free convection flow of a thermomicropolar fluid past a non-isothermal vertical flat plate

Laminar free convection boundary layer flow of a thermomicropolar fluid past a non-isothermal vertical flat plate has been studied in detail. It has been established that the flow problem has similarity solutions when the variation in the temperature of the plate is a linear function of the distance from the leading edge measured along the plate. The resulting system of the nonlinear ordinary differential equations has been solved numerically by “Shooting Method” for various values of the material parameters. The effects of these parameters has been studied on the velocity and microrotation fields graphically. Also “Tables” have been given for the values of temperature, skin-friction parameter, microrotation gradient on the wall and Nusselt number. Two types of boundary conditions are prescribed for the microrotation on the wall.     

Targeting DNA G‐Quadruplexes with Helical Small Molecules

We previously identified quinoline‐based oligoamide helical foldamers and a trimeric macrocycle as selective ligands of DNA quadruplexes. Their helical structures might permit targeting of the backbone loops and grooves of G‐quadruplexes instead of the G‐tetrads. Given the vast array of morphologies G‐quadruplex structures can adopt, this might be a way to achieve sequence selective binding. Here, we describe the design and synthesis of molecules based on macrocyclic and helically folded oligoamides. We tested their ability to interact with the human telomeric G‐quadruplex and an array of promoter G‐quadruplexes by using FRET melting assay and single‐molecule FRET. Our results show that they constitute very potent ligands—comparable to the best so far reported. Their modes of interaction differ from those of traditional tetrad binders, thus opening avenues for the development of molecules specific for certain G‐quadruplex conformations.     

The role of alloying elements in the design of nickel-base superalloys

The constituents of nickel-base superalloys have been classified into solid solution formers, precipitate formers, carbide formers and surface stabilizers. The characteristics of solutes which would make them most suitable in each category have been specified and appropriate alloying elements have been identified. Nickel-base superalloys are hardened primarily by the precipitation of Ni₃X type compounds. The occurrence and crystallography of precipitation of various kinds of Ni₃X type precipitates have been considered. The role of substitution by alloying elements on mismatch and stability of phases has been discussed. The free electron model and the Engel-Brewer model have been applied for evaluating the stabilities of precipitates, and the role of the alloying elements in determining the stabilities of external and internal surfaces such as grain boundaries have been briefly outlined.     

Kinetics of the thermal dissociation of Co4S3 under reduced pressure

Kinetics of the thermal dissociation of Co₄S₃ were investigated under reduced pressures of 5 × 10^-2 and 1.5 × 10^-4 mm Hg in the temperature range 1120° to 1405°C. The initial 10 pct dissociation was found to take place in accordance with a linear rate law, with activation energies of 20 and 17 kcal per mole under low and high vacuums, respectively. Subsequent dissociation up to about 35 pct was observed to be parabolic in nature, with activation energies of 38 and 40 kcal per mole under the respective vacuums. Further dissociation up to about 90 pct was found to fit into another linear rate law, with activation energies of 47 and 49 kcal per mole under the reduced pressures of 5 × 10^-2 and 1.5 × 10^-4 mm Hg, respectively. Beyond 90 pct, the dissociation was found to be very sluggish. These results have been interpreted with the help of the Co-S phase diagram. It has also been possible to achieve more than 99 pct dissociation of Co₄S₃ in 2 hr at 1405°C under low vacuum or 1355°C under high vacuum.     

Studies on the kinetics of carbon tetrachloride chlorination of tantalum pentoxide

Studies on the kinetics of chlorination of tantalum pentoxide powder by carbon tetrachloride vapor in dilution with nitrogen have been carried out by weight-loss measurements in two temperature ranges, i.e., 698 to 773 K and 793 to 853 K. The effect of time, temperature, and partial pressure of CCl₄ on the kinetics of chlorination of the powder Ta₂O₅, (−105+74 μm) has been investigated. In both the temperature ranges, the chlorination results have been found to fit the following relationship during the “initial periods:”

On the dilute solutions of gold in Bi-Sn alloys

The relative partial gram-atomic enthalpy of gold Δ?H_Au at infinite dilution in bismuth, tin, and six Bi-Sn alloys has been measured at 623°K. The composition dependence (dΔ?H_Au/dx _Au)_xAu→0 in bismuth and two Bi-Sn alloys and the temperature coefficient (dΔ?H_Au,_xAu→0)/dT in three Bi-Sn alloys have also been measured. An analysis of the results based on the quasichemical theory shows that (dΔ?H_Au/dx _Au)xAu→0) is very sensitive and Δ?H_Au,xAu→0 is insensitive to nonzero values of the relative energy of solute-solute bonds; the analysis also shows that a decrease in the coordination number has a small effect on (dΔ?H_Au/dx _Au)_xAu→0 but has an appreciable effect on Δ?H_Au,xAu→0