Disc coatings

On discs coated with Zdol films 62 A thick or more, droplets with lateral dimensions of tens of micrometers were observed in some areas of the surface, as shown in Figure 16. Apart from that, however, most of the surface was uniform unless disturbed by contact with the SPFM tip. After such contact, a droplet was usually formed due to capillary effects. Once formed, the droplet slowly grows in volume, indicating that the film was in a metastable state. However, no detectable layering in the surrounding region was observed. 

A very efficient thin layer form of circular paper chromatography makes use of a circular glass disc coated with an adsorbent (silica, alumina or cellulose). The apparatus is called a Chromatotron (available from Harrison Research, USA). The disc is rotated by a motor, and the sample followed by the eluting solvent are allowed to drip onto a central position on the plate. As the plate rotates the solvent elutes the mixture, centrifugally, while separating the components in the form of circles radiating from the central point. When elution is complete the revolving circular plate is stopped and the circular bands are scraped off and extracted with a suitable solvent. 

In their work, Andrieux and Saveant analyse the behaviour in terms of the characteristic current densities for each process. This has the advantage that, in general, the expressions for these characteristic current densities are fairly straightforward and obvious and, therefore, easily derived. In the case where the different processes involved are strictly first-order, the reciprocal of total current density can be obtained by combining the reciprocals of the current densities for the individual steps. For example, the limiting current density, //., for a reaction at the surface of a rotating disc coated by a permeable membrane is given by... 

Fig. 12 Detection in neat serum, a 1 x L of HSV gD at 5 x 10 particles/mL in calf serum incubated for 40 min on a quartz resonator coated with anti-gD IgG monoclonal antibody, then washed with water and scanned under 10 jl L of PBS from 0-10 V. b Calf serum only incubated for 40 min on a QCM disc coated with anti-gD IgG monoclonal antibody, then washed with water and scanned under 10 xL of PBS from 0-10 V...

Coatings suitable for lens replication have to share a number of properties with optical disc coatings such as a high optical transparency at the wavelength of the laser light, good hardness and abrasion resistance, high chemical and dimensional stability. 

The above trend was confirmed by Hull and Kitchener [39] using a rotating disc coated with a negative film and negative polystyrene latex particles. The number of polystyrene particles deposited was found to increase with increasing NaCl concentration, reaching a maximum at CnsO > 10 mol dm . The ratio of maximum number of particles deposited Nmax to the number deposited at any other NaCl concentration Nj (the so-called stability ratio W) was calculated and plotted versus NaCl concentration. 

The experiments reported here make use of the Thin Film Colorimetric Interferometry technique for film thickness measurement. In this technique, 3 X 8 bit SXGA still pictures are after transformation from RGB to CIELAB colour space converted to the film thickness map using appropriate colour/film thickness calibration curves. They are obtained from Newton rings for static contact formed between the steel ball and the glass disc coated with the chromium layer only. During several last years the accuracy and resolution of TFCI has been improved and it is now able to measure film thickness to within 1 nm [13]. 

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