Quartz crystal microbalance based on torsional piezoelectric resonators.

A quartz crystal microbalance (QCM) is described, which is based on a torsional resonator, rather than a conventional thickness-shear resonator. Typical applications are measurements of film thickness in the coating industry and monitoring of biofouling. The torsional QCM is about a factor of 100 less sensitive than the conventional QCM. On the other hand, it can probe film thicknesses in the range of hundreds of microns, which is impossible with the conventional QCM due to viscoelastic artifacts. Data acquisition and data analysis proceed in analogy to the conventional QCM. An indicator of the material's softness can be extracted from the bandwidth of the resonance. Within the small-load approximation, the frequency shift is independent of whether the sample is applied to the face or to the side of the cylinder. Details of the geometry matter if the viscoelastic properties of the sample are of interest.

Electrophoretic analysis of gold nanoparticles: size-dependent electrophoretic mobility of nanoparticles.

Efforts were made to realise a two-dimensional, on-line-coupled isotachophoresis-capillary zone electrophoresis system. The electrophoretic behaviour of gold nanoparticles was investigated with the idea that they could be used to improve the control of this electrophoretic set-up. The well-known citrate-ligated gold nanoparticles were not suitable for this application, because the ligand was desorbed, and the nanoparticle solutions were degraded. Therefore mercaptocarboxylic acids were used, because the chemisorption of thiols on the gold surface was improved. Isotachophoretic measurements were carried out with these nanoparticles. A size-dependent electrophoretic mobility was found according to theoretical predictions, and the surface and zeta-potential were discussed for the small particle range. A new method for concentration measurements of nanoparticles is presented by means of isotachophoresis.