I currently disperse Printex90 stock solution ( in distill water) with 5mins sonication bath, 30s sonication probe and 5 mins sonication bath again. all the procedures are processed on ice. But using the Zetasizer to detect the Dynamic Light Scater shows a lager Z-average size around 300nm. What strange is when I retest it after half an hour it shows smaller diameter (106nm) but with poor quality ( polydisperse).
The work solution (in medium) display 200-250nm diameter and has a relatively small second peak in intesity-size distribution(