Fluoro-surfactant as a tool for both controlling and measuring the size of the organoclay aggregates

A novel technique based on steady state fluorescence measurements was developed to study the cluster-cluster aggregation and sedimentation kinetics of an organoclay, SB-1, a quaternary ammonium compound of smectite clay. Pyranine (8-hydroxypyrene-1, 3, 6-trisulphonic acid, trisodium salt; POH) was used as a fluoro-surfactant, for which the maximum of the spectra appears at 510 nm wavelength in pure water above pH5.5. The maximum shifts to 430 nm wavelengths when pyranine is bonded to the organoclay particles via electrostatic interactions. It was observed that the average size of the aggregates increases above a critical pyranine/organoclay ratio, ∼0.1 (w/w), due to the "bridging" effect of pyranine, while it acts as a deflocculant for lower pyranine/organoclay ratios. It was shown that the fluorescence intensity from the pyranine bonded-aggregates monitors the average size of these aggregates, and that changes in the intensity during the sedimentation process can be used to measure the fractal dimension of the aggregates as a function of the organoclay concentration.