Influence of relative refractive index on optical properties of emulsions

The influence of refractive index on the optical properties of 4 wt.% n-hexadecane oil-in-water emulsions with the same droplet diameter (1 μm) and refractive index (n_d=1.43), but different aqueous phase refractive index (n_aq=1.33–1.46) was examined in the absence and presence of red dye. As the n_d/n_aq ratio moved away from one (either higher or lower), the scattering efficiency of the emulsion droplets increased. This caused the emulsion appearance to go from transparent to opaque, with a corresponding increase in spectral reflectance, L-value and turbidity. The spectral reflectance and tristimulus values of the dyed emulsions predicted by light scattering theory were compared with measured values. The spectral reflectance and L-value predicted by the theory showed similar trends to measured spectra, but the a- and b-values showed opposite trends. Three approaches have been proposed to correct this discrepancy.