Effects of

Effects of cetyltrimethylammonium bromide (CTABr) micelles on second-order rate constants (k(n)(obs)) for nucleophilic reactions of amines (piperidine and n-butylamine) with ionized phenyl salicylate (PS(-)) reveal a nonlinear decrease with the increase in [D(n)] (where [D(n)] = [CTABr](T) - cmc) at a constant [NaBr] and 35 degrees C. The observed data, at a constant [NaBr], fit reasonably well to a pseudophase model of micelles, and such a data fit gives kinetic parameters such as CTABr micellar binding canstant (K(S)) of PS(-). The effect of [NaBr] upon K(S) is explained with the empirical relationship K(S) = K(S)(0)/(1 + psi[NaBr]), where psi is an empirical parameter.     

Effects of Nonionic, Cationic, and Mixed Nonionic-Cationic Surfactants on the Acid-Base Behavior of Phenyl Salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35–CTABr micelles on the acid–base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile. The apparent pK_b (pK^app_b) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pK^app_b remain almost independent of [CTABr] within its range 0.01–0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pK^app_b. This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions.     

Dynamic Mechanical Properties of Activated Carbon–Filled Epoxy Nanocomposites

Nano-activated carbons obtained from oil palm empty fiber bunch (AC-EFB), bamboo stem (AC-BS), and coconut shells (AC-CNS) were reinforced in epoxy matrix to fabricate epoxy nanocomposites. The dynamic mechanical analysis of epoxy nanocomposites was carried out, and 5% AC-CNS treated with KOH-filled epoxy composites displayed the highest storage modulus of all the activated carbon–filled epoxy composites. The incorporation of a small amount of AC-BS, AC-EFB, and AC-CNS to the epoxy matrix enhanced the damping characteristics of the epoxy nanocomposites. The 5% AC-EFB treated with H₃PO₄ filled epoxy composites showed the highest glass transition temperature (T_g) in all temperature ranges.     

Unsteady shrinking sheet with mass transfer in a rotating fluid

In this paper, the problem of unsteady flow induced by a shrinking sheet with mass transfer in a rotating fluid is studied. The transformed boundary layer equations are solved numerically by an implicit finite‐difference scheme known as the Keller‐box method. The influence of rotation, unsteadiness and mass suction parameters on the reduced skin friction coefficients f″(0) and g′(0), as well as the lateral velocity and velocity profiles are presented and discussed in detail. Copyright © 2010 John Wiley & Sons, Ltd.     

Stagnation-point flow past a shrinking sheet in a nanofluid

In this paper, the stagnation-point flow and heat transfer towards a shrinking sheet in a nanofluid is considered. The nonlinear system of coupled partial differential equations was transformed and reduced to a nonlinear system of coupled ordinary differential equations, which was solved numerically using the shooting method. Numerical results were obtained for the skin friction coefficient, the local Nusselt number as well as the velocity and temperature profiles for some values of the governing parameters, namely the nanoparticle volume fraction φ, the shrinking parameter λand the Prandtl number Pr. Three different types of nanoparticles are considered, namely Cu, Al₂O₃ and TiO₂. It was found that nanoparticles of low thermal conductivity, TiO₂, have better enhancement on heat transfer compared to nanoparticles Al₂O₃ and Cu. For a particular nanoparticle, increasing the volume fraction φ results in an increase of the skin friction coefficient and the heat transfer rate at the surface. It is also found that solutions do not exist for larger shrinking rates and dual solutions exist when λ < −1.0.     

Seeded Polymerization of an Amide-Functionalized Diketopyrrolopyrrole Dye in Aqueous Media

The self-assembly of an amide-functionalized dithienyldiketopyrrolopyrrole (DPP) dye in aqueous media was achieved through seed-initiated supramolecular polymerization. Temperature- and time-dependent studies showed that the spontaneous polymerization of the DPP derivative was temporally delayed upon cooling the monomer solution in a methanol/water mixture. Theoretical calculations revealed that an amide-functionalized DPP derivative adopts an energetically favorable folded conformation in the presence of water molecules due to hydration. This conformational change is most likely responsible for the trapping of monomers in the initial stage of the cooperative supramolecular polymerization in aqueous media. However, the monomeric species can selectively interact with externally added fragmented aggregates as seeds through concerted π-stacking and hydrogen-bonding interactions. Consequently, the time course of the supramolecular polymerization and the morphology of the aggregated state can be controlled, and one-dimensional fibers that exhibit a J-aggregate-like bathochromically shifted absorption band can be obtained.     

MHD stagnation-point flow and heat transfer towards stretching sheet with induced magnetic field

The problem of the steady magnetohydrodynamic (MHD) stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The nonlinear partial differential equations are transformed into ordinary differential equations via the similarity transformation. The transformed boundary layer equations are solved numerically using the shooting method. Numerical results are obtained for various magnetic parameters and Prandtl numbers. The effects of the induced magnetic field on the skin friction coefficient, the local Nusselt number, the velocity, and the temperature profiles are presented graphically and discussed in detail.     

Mixed convection boundary layer flow along vertical moving thin needles with variable heat flux

The problem of steady laminar mixed convection boundary layer flow of an incompressible viscous fluid along vertical moving thin needles with variable heat flux for both assisting and opposing flow cases is theoretically considered in this paper. The governing boundary layer equations are first transformed into non-dimensional forms. The curvature effects are incorporated into the analysis whereas the pressure variation in the axial direction has been neglected. These equations are then transformed into similarity equations using the similarity variables, which are solved numerically using an implicit finite-difference scheme known as the Keller-box method. The solutions are obtained for a blunt-nosed needle (m = 0). Numerical calculations are carried out for various values of the dimensionless parameters of the problem, which include the mixed convection parameter λ, the Prandtl number Pr and the parameter a representing the needle size. It is shown from the numerical results that the skin friction coefficient, the surface (wall) temperature and the velocity and temperature profiles are significantly influenced by these parameters. The results are presented in graphical form and are discussed in detail.     

Room temperature LPG resistive sensor based on the use of a few-layer graphene/SnO<Subscript>2</Subscript> nanocomposite

A nanocomposite consisting of a few layers of graphene (FLG) and tin dioxide (SnO₂) was prepared by ultrasound-assisted synthesis. The uniform SnO₂ nanoparticles (NPs) on the FLG were characterized by X-ray diffraction in terms of lattice and phase structure. The functional groups present in the composite were analyzed by FTIR. Electron microscopy (HR-TEM and FE-SEM) was used to study the morphology. The effect of the fraction of FLG present in the nanocomposite was investigated. Sensitivity, selectivity and reproducibility towards resistive sensing of liquid propane gas (LPG) was characterized by the I-V method. The sensor with 1% of FLG on SnO₂ operated at a typical voltage of 1 V performs best in giving a rapid and sensitive response even at 27 °C. This proves that the operating temperature of such sensors can be drastically decreased which is in contrast to conventional metal oxide LPG sensors.

Open image in new window

Graphical abstract Schematic of a room temperature gas sensor for liquefied petroleum gas (LPG). It is based on the use of a few-layered graphene (1 wt%)/SnO₂ nanocomposite that was deposited on an interdigitated electrode (IDEs). A sensing mechanism for LPG detection has been established.