Fully-developed pipe and planar flows of multimode viscoelastic fluids

Two solutions are presented for fully-developed pipe and planar flows of multimode viscoelastic models. The fluids have a Newtonian solvent contribution and the polymer modes are described by the Phan-Thien—Tanner (PTT), the FENE-P or the Giesekus equation. The first solution is exact and can handle any number of modes, but is only semi-analytical. The second solution, which is presented only for the PTT model with a linear stress coefficient and the FENE-P model, can also handle any number of modes. It is based on a truncated series expansion and is completely analytical, but provides only an approximated solution. The complexity of the multimode solutions is investigated first with the exact semi-analytical method and it is shown that at high Deborah number flows the high-order stresses can become as important as the stress of the first mode. It is also under these conditions that the approximated analytical solution deviates from the exact semi-analytical solution. A criterion for the accurate use of the approximated solution is presented. Fortran codes are provided to obtain these solutions at the internet address at the end.     

An insight into Faradaic phenomena in activated carbon investigated by means of the microelectrode technique

Cyclic voltammetry was performed on activated carbon particles in a microelectrode setup to investigate the behaviour of an activated carbon with oxygen functionalities. Quinoid type redox peaks were clearly seen in the potential region around −0.5 V vs. Hg/HgO. After polarization below −0.4 V, an anodic peak confirms previous studies using a pristine carbon, but in the present work much higher in intensity. In addition, a corresponding cathodic peak, not previously reported, was also found. The appearance of this pair of peaks in a functionalized carbon may be connected to reversible hydrogen adsorption together with Faradaic reactions involving oxygenated functional groups.     

Nanotubes based composites rich in nitrogen for supercapacitor application

Exceptional conducting and mechanical properties of multiwalled carbon nanotubes (Nts) used for carbonisation a polymer blend of melamine (M) and formaldehyde (F) enabled to prepare a unique Nt-composite rich in nitrogen. Using a different proportion of Nts and a polymer blend, a series of composites with a comparable texture (surface area of ca. 400 m²/g) but variable N content ranging from ca. 7 to 20 wt% has been obtained without any activation process. A detailed analysis of physicochemical properties of composites has been performed and correlated with supercapacitor characteristics. Composite with ca. 12 wt% of nitrogen showed the best charge propagation, its mesoporous network allowed a pseudocapacitance effect of nitrogen to be efficiently used.     

The use of a modified Multimode Sample Introduction System for the simple and rapid determination of cadmium by chemical vapour generation atomic absorption spectrometry

A cold vapour (CV) generation system incorporating a modified version of a Multimode Sample Introduction System (MSIS™) was investigated for the determination of cadmium by atomic absorption spectrometry (AAS). The system allowed for the use of the relatively high concentrations of reagents required for efficient production of volatile cadmium without the significant bubbling, frothing, and associated liquid transport problems common to conventional gas–liquid separators while maintaining a low volume. The low volume produced narrow peaks (approximately 5 s base peak width). A detection limit of 0.026 μg L⁻¹ (3s) was found with a precision of 2.5% for a 0.5 μg L⁻¹ standard (n=4) and a linear dynamic range up to approximately 10 μg L⁻¹. The addition of thiourea, cobalt, and nickel was found to overcome interferences and produce good agreement between experimental and certified values for Natural Water and Mussel Tissue standard reference materials (SRM).     

Protonation and complex formation of the cis and trans isomers of alicyclic β-amino acids

The protonation constants of β-alanine and the cis and trans isomers of aliphatic 2-amino-1-carboxylic acids containing a cyclohexane, cyclopentane or cyclohexene(4) ring were determined pH-metrically, as were the formation constants of their complexes with Ni²⁺, Cu²⁺, Hg²⁺ and Cd²⁺ ions. The analysis of about 70 formation constants revealed significant differences betweeen the behaviours of the different ligands, each of which has a fixed β-alanine conformation. It is concluded that complex formation is primarily determined by the nature of the fixed β-alanine conformation and in some cases by the type of aliphatic ring.     

A dynamical model for liquid water

Anomalies in liquid water are attributed to librational/rotational motions, which depend cooperatively on H-bond structure within relatively stable oxygen groupings. The close relationships between small-ion hydration dynamics, spin-lattice and dielectric relaxation times, and shear viscosity are delineated. Within this context, the anomalous heat capacity of Oguni and Angell can be understood.     

Luminescence of iron(III): In zircon-structured phosphates MPQ4 (M = Sc,Lu, Y)

Luminescence and decay time measurements are presented for Fe³⁺ -doped ScPO₄, LuPO₄ and YPO₄. The Fe³⁺ ion gives a red luminescence. A consistent interpretation of the luminescence data is possible by assuming that the Fe³⁺ ion in ScPO₄ is surrounded by four oxygen ions within a relatively weak crystal field and in LuPO₄ and YPO₄ by eight oxygen ions within a relatively strong crystal field.     

Determination of particle size in the range below 10 Å for ultrathin films of Pt/C

The phenomenon of clustering and its influence on the catalytic activity of the Pt/C system is studied. Coverages of the order of 10¹² atoms/cm² were used. Calculations permit the estimation of the most active particles as dimers and other large particles of the B₄ and B₅ site types.     

Application of NMR spectroscopy in molecular weight determination of polymers

Determination of molecular weights of polymers by ¹H-NMR spectroscopy is discussed. A brief survey of application of NMR; both ¹H and ¹⁴C, in the analysis of monomer sequence, copolymer composition, polymer microstructure, end-group and relaxation phenomenon is also made. NMR offers an elegant and simple yet fairly accurate method for determination of molecular weights of polymers.