This paper describes the ultrasound assisted dispersal of a low wt. / vol. % copper nanopowder mixture and determines the optimum conditions for deagglomeration. A commercially available powder was added to propan-2-ol and dispersed using a magnetic stirrer, a high frequency 850 kHz ultrasonic cell, a standard 40 kHz bath and a 20 kHz ultrasonic probe. The particle size of the powder was characterized using dynamic light scattering (DLS). Zaverage diameters (mean cluster size based on the intensity of scattered light) and intensity, volume and number size distributions were monitored as a function of time and energy input. Low frequency ultrasound was found to be more effective than high frequency ultrasound at de-agglomerating the powder and dispersion with a 20 kHz ultrasonic probe was found to be very effective at breaking apart large agglomerates containing weakly bound clusters of nanoparticles. In general, the breakage of nanoclusters was found to be a factor of ultrasonic intensity, the higher the intensity the greater the deagglomeration and typically micron sized clusters were reduced to sub 100nm particles in less than 30 min using optimum conditions. However, there came a point at which the forces generated by ultrasonic cavitation were either insufficient to overcome the cohesive bonds between smaller aggregates or at very high intensities decoupling between the tip and solution occurred. Absorption spectroscopy indicated a copper core structure with a thin oxide shell and the catalytic performance of this dispersion was demonstrated by drop coating onto substrates and subsequent electroless copper metallization. This relatively inexpensive catalytic suspension has the potential to replace precious metal based colloids used in electronics manufacturing.

The optical and electrical properties of dodecanethiol-stabilized nanoparticles (6 nm diameter gold core) have been investigated over a range of film thicknesses and temperatures. The surface plasmon resonance absorbance is found to be dependent on temperature. Heating of the nanoparticle film causes desorption of the thiol from the surface of the gold nanoparticle, resulting in irreversible changes to the absorption spectra of the nanoparticle film. Atomic force microscopy images of the samples before and after heating for different film thicknesses reveal structural changes and increased domain connectivity for thicker films leading to sub-10 ohm resistances measured for the 15-layer film.

We deposit dense, ordered, thin films of Au-dodecanethiol core/shell nanoparticles by the Langmuir-Schäfer (LS) printing method, and find that their resistance at ambient temperature responds selectively and sensitively to alkane odours. Response is a rapid resistance increase due to swelling, and is strongest for alkane odours where the alkane chain is similar in length to the dodecane shell. For decane odours, we find a response to concentrations as low as 15 ppm, about 600 times below the lower explosive limit.Response is weaker, but still significant, to aromatic odours (e.g. Toluene, Xylene), while potential interferants such as polar and/or hydrogen-bonding odours (e.g. alcohols, ketones, water vapour) are somewhat rejected. Resistance is weakly dependent on temperature, and recovers rapidly and completely to its original value within the error margin of measurement.

The ability of calixarene based molecules to interact with amino acids has been the basis of many studies. The Langmuir and LB properties of two calix[4]resorcinarenes have been investigated. The properties of the layer formed at the air-water interface were studied by surface pressure area isotherms. LB deposition onto glass substrates has shown that multilayer assemblies can be built up. The UV-visible spectra of resulting LB films have been recorded, indicating that the compounds are coloured as a result of intra-molecular charge transfer bands. The sensitivity of the surface pressure area isotherms has been investigated in relation to the exposure to various analytes delivered from the subphase (i.e. amino acids). Furthermore, exposure of the LB films to a wide range of vapours (e.g. amines, alcohols, thiols) has led to modified UV-visible spectra.

No abstract