Theoretical and Experimental Study of Spectral Reflectance and Color of Concentrated Oil-in-Water Emulsions

The influence of droplet and dye concentration on the optical properties of oil-in-water emulsions has been investigated. The spectral reflectance and tristimulus color coordinates (L, a, b) of a series of n-hexadecane oil-in-water emulsions with the same median droplet diameters ( approximately 0.3 µm), but different droplet concentrations (0.25 to 38.3 wt%) and red dye concentrations (0 to 0.2 wt%), were measured. Spectral reflectances decreased with increasing dye concentration and decreasing droplet concentration and had troughs at the same wavelengths as the peaks in the absorption spectra of the dyes. Emulsion L-values ("lightness") decreased and a- and b-values ("chromacity measures") increased as the dye concentration increased or the droplet concentration decreased. There was good qualitative agreement between the measured spectral reflectance of the emulsions and that predicted by the Kubelka-Munk theory of diffuse reflectance. Excellent agreement between theory and experiment could be obtained using an empirically determined correction-factor that accounts for cuvette effects. Copyright 1999 Academic Press.