Effect of mass transport processes on physicochemical properties of surfactant -stabilized emulsions
The mechanism of molecular mass transport processes such as solubilization and Ostwald ripening in surfactant stabilized oil-in-water emulsions and the effect on their bulk physicochemical properties was investigated.
Solubilization was slightly influenced by the initial emulsion droplet size. The smaller the droplets were, the faster the oil molecules were incorporated into surfactant micelles. During solubilization, the droplet size of the emulsion increased. This increase was more pronounced for emulsions with low oil droplet concentrations and small droplet sizes. Solubilization was influenced by the nature of the dispersed phase. Small molecular weight n-hydrocarbons were rapidly solubilized. Triglycerides could not be incorporated in micelles due to their large molecular weight. The nature and concentration of surfactant micelles; also influenced solubilization kinetics. Surfactant micelles with HLB numbers close to seven incorporated more oil more rapidly than surfactants with larger HLB numbers.
The growth of oil droplets in surfactant stabilized emulsions during solubilization experiments was due to Ostwald ripening. Ostwald ripening depended on the nature of the oil droplets. Low molecular weight hydrocarbons had a higher solubility in the aqueous phase and therefore aged more quickly than high molecular weight compounds. Ostwald ripening was accelerated by the presence of surfactant micelles that acted as carriers between emulsion droplets. A larger number of surfactant micelles therefore resulted in increased Ostwald ripening rates. Surfactants that were highly surface-active and consequently had a higher diffusion coefficient accelerated Ostwald ripening strongly. Both Ostwald ripening and solubilization were accelerated in emulsions were surfactant micelles were present. In comparison, solubilization proceeded faster than Ostwald ripening.
Finally, the effect of mass transport processes emulsion rheology and color was investigated. Ostwald ripening influenced the rheology of emulsions. Emulsions made with n-hexadecane exhibited a rapid solid-liquid. like transition whereas the rheological properties of n-octadecane emulsion droplets did not change significantly during the course of the experiment. Ostwald ripening also influenced the color of emulsions that contained a red dye in the aqueous phase. Aging experiments conducted on n-hexadecane emulsion droplets did show significant color changes with time whereas n-octadecane emulsion droplets retained their color during the course of the experiment.
0542: Chemical engineering