A NEW HYDROSOL OF GOLD CLUSTERS .2. A COMPARISON OF SOME DIFFERENT MEASUREMENT TECHNIQUES

An aqueous colloidal gold dispersion previously assessed by UV-visible extinction spectrophotometry to have a mean diameter of 1-2 nm has been subjected to transmission electron microscopy, analytical ultracentrifugation, X-ray diffraction, and cluster development experiments. Cluster coalescence under the electron beam has been shown to have a significant influence on the particle size distribution measured by TEM, even where the 'steric stabilizer'' gelatin is used. Cluster combination in sol is also indicated upon development to larger size using hydroxylamine hydrochloride. In solid- as well as sol-state powder X-ray diffraction, a very broad line is seen. Although all these techniques are in basic agreement with a mean particle size of 1-2 nm, their inherent limitations in probing an ensemble of clusters of these dimensions are outlined.