A STUDY OF THE DISPERSAL OF ALUMINUM HYDROXYCARBONATE GEL USING A FIBER OPTIC DOPPLER ANEMOMETER (FODA) (SUSPENSION-STABILITY, PARTICLE INTERACTIONS, AUC)
Abstract
The application of fiber optic Doppler anemometry (FODA) to the study of the dispersal of aluminum hydroxycarbonate suspensions was examined using the integrated area under the curve (AUC) from the power spectrum output. Three dispersing agents were used in this study. These include sodium metaphosphate (polyelectrolyte type), sodium lauryl sulfate (anionic surface active agent), and poly(vinylalcohol) (polymeric type). From the AUC monitoring, together with the sediment height from the sedimentation volume study, it was found that changes in AUC with time can be related to changes in the PZC-pH relationship. The experimental observations demonstrated that the point of zero change is changed by sodium metaphosphate and sodium lauryl sulfate adsorption. Increasing concentrations of sodium metaphosphate and sodium lauryl sulfate caused changes in the AUC from FODA and the electrical surface potential of carbonate-containing aluminum hydroxide suspensions although the magnitude of this effect was found to be dependent on the initial pH of the suspensions. The effect of particle size in the dispersing action of sodium metaphosphate was investigated using three standard polymeric latexes dispersions at a constant volume fraction. A very fast flocculation was observed as the particle size decreased. FODA was able to demonstrate the importance of the surface anchor groups in the mechanism of action of a steric stabilizer. The effect of poly(vinylalcohol) on aluminum hydroxycarbonate gel showed a concentration dependence. At very low concentrations, the predominant effect observed is bridging flocculation. At higher concentrations, steric stabilization was observed. At even higher concentrations, depletion flocculation was observed and, finally, at the highest poly(vinylalcohol) concentrations, depletion stabilization was observed. The state of dispersion determined by the AUC from FODA was confirmed by: (1) sediment height from sedimentation volume, (2) rheological data including apparent viscosity in the case of polymeric type dispersing agents, and (3) agreement with the DLVO theory and the steric stabilization mechanism.
Degree
Ph.D.
Subject Area
Pharmaceuticals
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