THE USE OF THE FIBER OPTIC DOPPLER ANEMOMETER (FODA) IN THE CHARACTERIZATION OF EMULSIONS (OPTIMAL SURFACTANT MIXTURE, DROPLET SURFACE CHARGE EFFECTS)
Abstract
The fiber optic Doppler anemometer (FODA) has been demonstrated to be a valuable tool for characterizing emulsion systems and for optimizing emulsion formulation and processing variables. The instrument was validated for droplet size determination of emulsions using a freeze etching SEM technique and is capable of detecting the presence of small droplets that previous sizing methods have neglected. Area under the curve (AUC) measurements are indicative of the number of droplets in free Brownian movement in an emulsion sample. The optimal nonionic surfactant mixture for an emulsion is determined by finding the surfactant ratio that yields a minimum droplet radius and maximum AUC. Minimal required surfactant levels can be determined by analysis of radius and AUC measurements. Mean droplet radius decreased with increasing surfactant levels up to a certain concentration. Higher surfactant levels did not lead to further droplet size reduction. AUC calculations increased to a maximum at a certain surfactant concentration and then additional surfactant did not produce appreciably more droplets. The minimal surfactant level could be correlated to the oil concentration of the emulsion. Processing conditions to produce the most droplet dispersion were established by FODA analysis. Mean droplet radius decreased while the AUC increased during the time of processing. Replacement of small amounts of nonionic surfactant in the emulsion formulation with ionic surfactants produced decreases in the oil concentration at which droplet interactions begin to occur. These changes were due to the changes in droplet surface charge due to the ionic surfactant present in the formulation. Initial hydrophilic surfactant placement has little effect on the final emulsion product for the optimized system.
Degree
Ph.D.
Subject Area
Pharmaceuticals
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