Azizah Mainal

A DFT study of the chemical and optical properties of 7-atom Ag–X [X = Li, Na] nanoalloys for potential applications in opto-electronics and catalysis

In this paper, Ag atoms are substituted by X (Li, Na) atoms to form AgmX(7−m) clusters to explore their electronic, chemical and optical properties in the framework of density functional theory (DFT). The clusters are geometrically optimized without imposing symmetry and later, vibrational analysis is carried out to test the stability of the optimized structures. The calculation of ionization potential and electron affinity asserted that the Li and Na doped bimetallic clusters (especially, Ag4Li3 and Ag3Li4) are very stable in the neutral state, but their anions are expected to be very reactive. The calculated absorption spectra of the AgmX7−m clusters have revealed that the doping of Li and Na has made the absorption band wider with regards to undoped Ag7 clusters. Therefore, this work suggests that Li and Na doping (especially, Ag4X3, Ag3X4 and Ag2X5 clusters) will result in improvement of the absorption band in the 1–5 eV range, which is the prime absorption band for opto-electronic devices such as solar cells.

Al–X and Cu–X [X = Li, Na] nano-alloys: a low cost alternative to silver and gold nanoparticles for plasmonic applications

We present a systematic study of the electronic and optical properties of the Li and Na doped Al–X and Cu–X (X = Li, Na) nanoalloys in the framework of density functional theory in order to evaluate their potential as low cost plasmonic materials as alternatives to silver and gold. A single atom in the 13 atoms Al and Cu clusters is replaced by the Li and Na atoms in the core and surface positions to form core-doped and surface-doped Al12X and Cu12X bimetallic clusters respectively. Vibrational analysis has ensured the structural stability of the doped clusters. Binding energies and HOMO–LUMO gaps are calculated to predict the electronic stability, as well as the ionization potential and electron affinity of the clusters. Large HOMO–LUMO gaps with small electron affinity of the doped clusters ensured that anions of the Cu12X and Al12X clusters will be very reactive. The optical absorption properties of the undoped and doped clusters are calculated in the framework of TDDFT. It is observed that the Li and Na doping into the Al and Cu clusters yield significant increase in the absorption band-gap in both of the Cu and Al clusters. In particular, the surface doped Al12X clusters exhibit remarkable large bandgap which comprises from 3 eV to 11 eV. Due to their electronic and optical properties, the Al–X and Cu–X doped clusters may be considered as an excellent low cost alternative to silver and gold, which can find its worth in catalytic, opto-electronic and UV-absorption applications.

Impact of aluminium addition on the corrosion behaviour of Sn–1.0Ag–0.5Cu lead-free solder

The effect of Al on the corrosion resistance behaviour of Pb-free Sn–1.0Ag–0.5Cu–xAl solder (x = 0.2 wt%, 0.5 wt% and 1.0 wt%) in 5% NaCl solution was investigated by using potentiodynamic polarization and salt spray exposure. Passivation behaviour was evident in all the solder formulations containing Al, compared to the base SAC solder. FESEM and XRD results revealed that more dense passive films were formed on the solder containing Al, compared to the base solder. These passivation films contained intermetallic compounds such as Al2O3, AlCuO4, SnO and SnO2 served to prevent further reaction on the material surface. Polarization studies showed that the corrosion rate was 30% and 6% lower for alloys with 0.5 wt% and 0.2 wt% Al content, respectively, even though the corrosion potential shifted towards more negative values. The Al-added solder alloys exhibit more refined surface after exposure in the salt spray chamber and revealed no visible infiltration of aggressive ions at the solder–substrate joint. This work suggests a corrosion mitigation strategy for SAC 105 solder through doping of Al.

Synthesis and characterisation of highly branched polyisoprene: exploiting the “Strathclyde route” in anionic polymerisation

This work aimed at developing a synthetic route towards highly branched poly(isoprene) from commercially available raw materials, in good yield and devoid of microgelation, i.e., to prepare a completely soluble polymer via the versatile technique anionic polymerisation. The polymerisations were conducted under high vacuum conditions using sec-butyllithium as initiator at 50 °C in toluene. Toluene served both as a solvent and as a chain-transfer agent. The polar modifier used was tetramethylethylenediamine (TMEDA), and a commercial mixture of divinylbenzene (DVB) was employed as the branching agent for the “living” poly(isoprenyl)lithium anions. The nature of the reaction was studied on the TMEDA/Li ratio as well as the DVB/Li ratio. The obtained branched polymers were characterised by triple detection size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC) and melt rheology. Broad molecular weight distributions have been obtained for the highly branched polymer products. 1H NMR spectroscopy reveals the dominance of 3,4-polyisoprene microstructure. It was found that the complex viscosities and dynamic moduli of the branched samples were much lower compared to their linear counterparts. The results conform with earlier findings by the “Strathclyde team” for radical polymerisation systems. This methodology has the potential of providing soluble branched vinyl polymers at low cost using the readily available raw materials.

Correction: Impact of aluminium addition on the corrosion behaviour of Sn–1.0Ag–0.5Cu lead-free solder

Correction for ‘Impact of aluminium addition on the corrosion behaviour of Sn–1.0Ag–0.5Cu lead-free solder’ by N. I. M. Nordin et al., RSC Adv., 2015, 5, 99058–99064.

Conductivity studies on the effect of a nematic liquid crystal on polyvinyl alcohol-based electrolytes

Recently, a few studies have shown that the introduction of liquid crystals (LCs) in polymer electrolytes would lead to an increase in the chain mobility and the ionic conductivity. It is believed that this enhancement of the polymer electrolyte performance is greatly influenced by the order parameter of the liquid crystal in this system. In this study, a deuterated 4-pentyl-4-cyano-biphenyl (5CB-d2) nematic liquid crystal-doped polyvinyl alcohol (PVA) polymer electrolyte were prepared. The orientational order of the nematic liquid crystal is then investigated via the quadrupolar splittings of the deuterium Nuclear Magnetic Resonance (NMR) spectra. The quadrapolar splitting, which is directly related to the orientational order of the liquid crystal director, was measured and compared between the embedded 5CB-d2 in the PVA electrolyte to that of the pure 5CB-d2. The conductivity of a 5CB-d2 embedded in PVA reached up to 3.28x10-1 S/cm compare to that of without 5CB-d2 which is only 2.89x10-1S/cm. The presence of 5CB-d2 in the PVA polymer electrolyte improved the electrical conductivity of the mixture through an improved charge transfer mechanism, which improves its electrical properties, a criterion useful for a device that needs high conductivity.

2-(4-Meth­oxy­phen­oxy)pyrazine

In the title compound, C11H10N2O2, the aromatic rings are almost orthogonal to each other [dihedral angle = 86.97 (8)°], with the benzene ring orientated to face one of the pyrazine N atoms. In the crystal, centrosymmetrically related pairs are connected via pairs of C—H⋯π interactions and the dimeric units thus formed pack into undulating layers that stack along the a axis.