Color changes in hydrocarbon oil-in-water emulsions caused by Ostwald ripening

The influence of Ostwald ripening on the optical properties of hydrocarbon oil-in-water emulsions stabilized by sodium dodecyl sulfate was investigate d. The droplet size, spectral reflectance, and tristimulus color coordinate s (L, a, and b) of a series of n-hexadecane and n-octadecane oil-in-water e mulsions were measured in the presence and absence of a water-soluble red d ye (FD&C Red No. 40). The droplets grew more rapidly in the emulsion contai ning n-hexadecane than in the emulsion containing n-octadecane because of t he higher solubility of n-hexadecane molecules in the aqueous phase. Ostwal d ripening caused appreciable changes in n-hexadecane emulsion spectral ref lectance and color L, a, and b values due to the growth of emulsion droplet s. L, a, and b color values and spectral reflectances of n-octadecane emuls ions did not significantly change during the course of the experiment. The results were explained in terms of Ostwald ripening theory and a previously described light scattering theory. The model enables emulsion manufacturer s to predict color changes in oil-in-water emulsions that exhibit transcond ensational ripening.