Showing papers by "Muhammad Kaleem Khosa published in 2016"

Halloysite reinforced epoxy composites with improved mechanical properties

Abstract: Abstract Halloysite nanotubes (HNTs) reinforced epoxy composites with improved mechanical properties were prepared. The prepared HNTs reinforced epoxy composites demonstrated improved mechanical properties especially the fracture toughness and flexural strength. The flexural modulus of nanocomposite with 6% mHNTs loading was 11.8% higher than that of neat epoxy resin. In addition, the nanocomposites showed improved dimensional stability. The prepared halloysite reinforced epoxy composites were characterized by thermal gravimetric analysis (TGA). The improved properties are attributed to the unique characteristics of HNTs, uniform dispersion of reinforcement and interfacial coupling.

Synthesis and characterization of new soluble thermally stable poly(azomethine‐ether‐imide)s: discerning the possibility for high temperature applications

Abstract: A new series of polyimides was synthesized by the condensation of monomers (azomethine-ether diamine, DA-1 and DA-2) with pyromelliticdianhydride (PMDA), 3,4,9,10-perylenetetracarboxylic dianhydride (PD) and 3,3'4,4'-benzophenonetetracarboxylic dianhydride (BD). The structural explications of monomers and polyimides was conducted by FT-IR, H-1 NMR and elemental analysis. All polyimides were found soluble in polar aprotic solvents and found to be semicrystalline in nature confirmed by XRD. The inherent viscosities were found in the range of 0.67-0.77 g/dl. %. Average molecular weight (MW) and number average molecular weight (Mn) of the polyimides were found in the range of 5.72 x 10(5) g/mol-6.58 x 10(5) g/mol and 3.79 x 10(5) g/mol 4.11 x 10(5) g/mol respectively. The polyimides exhibited excellent thermal properties having a glass transition temperature T-g in the range of 230-290 degrees C and the 10% weight loss temperature was above 450 degrees C. The values of thermodynamic parameters, activation energy, enthalpy and entropy fall in the range of 45.2-53.90 kJ/mol, 43.5-52.30 kJ/mol and 0.217 kJ/mol k to 0.261 kJ/mol k respectively. Copyright (C) 2015 John Wiley & Sons, Ltd.

Excess molar volume and isentropic compressibility of monoethanolamine in aqueous system at temperatures from 298.15 to 318.15 K

Abstract: Densities and sound velocities for aqueous monoethanolamine (MEA) system are reported over the entire composition range at different temperatures (298.15, 303.15, 313.15 and 318.15 K). These experimental data have been further used in calculating the excess molar volume, partial molar volumes, isobaric thermal expansion coefficients and the deviation in isentropic compressibility. The excess molar volumes data were fitted to the Redlich–Kister polynomial equation to obtain their coefficients and standard deviations. The partial molar volume at infinite dilution of both water in MEA and MEA in water and have been determined using two different methods. Knowledge of the above properties of these mixtures is a basis for understanding some of the molecular interactions in these systems. From the analysis of the results, the type of interactions between the MEA and water is discussed in terms of the number and size of the alkyl groups attached to the nitrogen atom of MEA.

Volumetric and Acoustic Behavior of Sodium Cyclamate in Aqueous System from 293.15 K to 318.15 K

Abstract: Density (ρ) and sound velocity (u) measurements were carried for aqueous solutions of sodium cyclamate (SC) from 293.15 to 318.15 K. Apparent molar and specific volumes, isentropic apparent molar compressibility and hydration numbers were computed from the experimental measurements. Apparent molar volumes (Φ V ) of SC show negative deviations from the Debye–Huckel limiting law and the values obtained for Φ V at given temperatures and concentrations were used as a direct measure of the ion–ion and ion–solvent interactions. Interactions causing a sweet taste require a specific volume to stimulate receptor sites from water and possibly also in the biophase. Furthermore, the partial molar expansibility (Φ ° ), Hepler’s constant (∂2 Φ ° /∂T 2 ) and thermal expansion coefficient have been estimated. This study will help to elucidate the structural interactions of SC with water and its taste in foods.

An unusual coordination polymer containing Cu+ ions and featuring possible Cu⋯Cu `cuprophilic' inter­actions: poly[di-μ-chlorido-(μ4-3,5-di­amino­benzoato-κ4O:O′:N:N′)tricopper(I)(3 Cu—Cu)]

Abstract: Compounds containing copper(I) are of inter­est for their role in biological pro­cesses. The nature of short (< ∼3.2 A) Cu⋯Cu contacts within these com­pounds has been debated, being either described as weakly attractive (bonding) `cuprophilic' inter­actions, or simply as short metal–metal distances constrained by ligand geometry or largely ionic in nature. The title three-dimensional Cu+-containing coordination polymer, [Cu3(C7H7N2O2)Cl2]n, was formed from the in situ reduction of CuCl2 in the presence of 3,5-di­amino­benzoic acid and KOH under hydro­thermal conditions. Its complex crystal structure contains ten distinct CuI atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near-linear CuOCl and CuN2, T-shaped CuOCl2 and distorted tetra­hedral CuOCl3 groups. Each CuI atom is also associated with two adjacent metal atoms, with Cu⋯Cu distances varying from 2.7350 (14) to 3.2142 (13) A; if all these are regarded as `cuprophilic' inter­actions, then infinite [\overline{1}01] zigzag chains of CuI atoms occur in the crystal. The structure is consolidated by N—H⋯Cl hydrogen bonds.