Michael J. Witcomb

Polymer stabilized silver nanoparticles: A photochemical synthesis route

This study describes a novel and convenient way for the preparation of polymer stabilized colloidal silver by an ultra-violet irradiation technique. Methoxypolyethylene glycol (MPEG) generates free radicals in presence of ultra-violet radiation and acts as the reducing agent towards the silver ion. MPEG also serves as a stabilizer of the silver particles formed.

Conjugated polymer stabilized palladium nanoparticles as a versatile catalyst for Suzuki cross-coupling reactions for both aryl and heteroaryl bromide systems

A simple and efficient procedure for Suzuki coupling of aryl bromides with phenylboronic acid, catalyzed by an in situ-generated palladium(0)–polymer composite in the absence of any phosphine ligand, has been reported. The catalyst is remarkably active having a high TOF value for both aryl and heteroaryl systems, and is recyclable up to three runs with minimum loss of efficiency.

The development of ion-bombardment surface structures on stainless steel

A brief review is given of the formation and characteristics of conical surface structures resulting from ion etching. The effect of low-energy ion bombardment of 18-8 stainless steel surfaces has been studied. The topography generated has been related to microstructural detail. The conical protrusions are found to arise from slag silicate particles while the pillar type structures result from fibrous manganese sulphide inclusions. Scanning electron microscopy has shown the development of both of these structure types to be in accord with previously published ion-etching models.

Prediction of the apex angle of surface cones on ion-bombarded crystalline materials

Different methods of calculation based on ion channelling in a target matrix have been applied to the computation of the apex angle of surface conical shapes derived from ion bombardment. Comparison with values obtained experimentally by electron microscopy and deduced from sputter yield curves in the energy range 0.2 to 27.0 keV indicate that reasonable agreement can be achieved using a smeared Thomas Fermi atomic plane potential.

A useful Mott-Efros-Shklovskii resistivity crossover formulation for three-dimensional films

Useful and simple 3D crossover expressions are presented for the resistance versus temperature behaviour in highly insulating 3D films. At high temperatures, this theory extrapolates to the Mott variable-range hopping law, and at low temperatures to the Efros - Shklovskii variable-range hopping law. Good agreement is found between the crossover theory and resistance measurements.

Low-temperature magnetic property of polymer encapsulated gold nanoparticles

Gold-polyaniline composite is reported by the polymerization of aniline hydrochloride monomer using HAuCl4 as the oxidant. HAuCl4 was dissolved in toluene using a phase-transfer catalyst, Aliquat 336. The oxidative polymerization of aniline hydrochloride leads to the formation of polyaniline with a diameter of <50 nm, while the reduction in auric acid results in the formation of gold nanoparticles with an average diameter ∼4 nm. The resultant composite material was characterized by means of different techniques, such as UV-vis, IR, and Raman spectroscopies, which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the polymer matrix. dc-magnetization measurements down to low temperatures (2 K) enabled the identification of a small, but field-independent paramagnetic behavior of the composite, and this is argued to originate from the charge t...

Directional assembly of polyaniline functionalized gold nanoparticles

Polyaniline encapsulated and functionalized self-assembled gold nanoparticles have been synthesized using an interfacial polymerization approach. The polyaniline and gold nanoparticles were formed at the aqueous and organic interface and a directional growth of the self-assembled gold nanoparticles was observed. The resultant composite material was characterized by means of different techniques. IR, Raman and UV–visible (UV–vis) spectra provided information on the chemical structure of the polymer. UV–vis spectrum also indicated the functionalization of the gold nanoparticles by the polymer. TEM images showed the morphology of the polymer and the metal particles.

Optical, microscopic and low temperature electrical property of one-dimensional gold―polyaniline composite networks

An in situ one pot synthesis route is described for the preparation of a gold–polyaniline nanocomposite material by polymerization of aniline hydrochloride using HAuCl4 as the oxidant. The resultant composite material was characterized by various techniques. The temperature-dependent electrical conductivity values were supportive of a thorough dispersion of metallic conducting centres and the interpretation is commensurate with the one-dimensional geometry of the composite material. The temperature dependence of the Hall coefficient of the gold–polymer composite is evidence of a possible contribution of a charge carrier deficit and a temperature-dependent mobility in this material.

Polymer‐Stabilized Palladium Nanoparticles for the Chemoselective Transfer Hydrogenation of α,β‐Unsaturated Carbonyls: Single‐Step Bottom‐Up Approach

Polypyrrole stabilised palladium nanoparticles show good catalytic efficiency for the chemoselective transfer hydrogenation of α,β‐unsaturated carbonyl compounds. The catalyst is very specific and selectively hydrogenates the olefins or acetylenes only, without affecting the carbonyl moiety, with an excellent yield of products for a wide range of substrates.

Palladium-Polyaniline and Palladium-Polyaniline Derivative Composite Materials

polymers from metals is their low electrical conductivity. A new class of organic polymers capable of conducting electricity has recently been developed (1, 2). These polymers become conductive upon partial oxidation or reduction, a process commonly referred to as ‘doping’. The electrical properties of conductive polymers can be changed reversibly over the full range of conductivity from insulators to metallic conductors. Their potential as novel materials in value-added industrial and consumer products is opening up wholly new avenues of application for polymeric materials. Among conducting plastics, polyaniline has become a particular focus of interest because of its environmental stability (3), controllable electrical conductivity (4), and interesting redox properties associated with the chain nitrogen (5). The electrical properties of the aniline polymers can be improved substantially by secondary doping (6). Polyaniline compounds can be designed to achieve the particular conductivity required for a given application. The resulting blends can be as conductive as silicon and germanium or as insulating as glass. Additional advantages are that the compound can be mixed simply with conventional polymers, and it is easy to fabricate polyaniline products into specific shapes. The conductivity of polyaniline makes it an ideal shield against static electric discharges, and as a consequence polyaniline compounds have been used in the packaging of electronics products. Polyaniline compounds are being tested for use as protective materials against electromagnetic radiation. Further, scientists hope that one day printed circuit boards, electrochromic windows in houses and cars, and conductive fabrics will contain polyaniline compounds. The presence of a number of intrinsic redox states (Figure 1) has substantially increased the number of potential applications of aniline polymers for use in practical devices. The aniline polymers have a general formula of the type [(–B–NH–B–NH–)y (–B–N=Q=N–)1–y]x, in which B and Q denote respectively the C6H4 rings in the benzenoid and the quinoid forms. In polyaniline, the neutral intrinsic redox states (Figure 1) can vary from that of the fully oxidised pernigraniline (PNA; y = 0), to that of the