A simple method for determination of surface volume mean diameters of oil in water submicron emulsions

Plots of the droplet size parameter, α = πnD/λ versus the total scattering coefficient or specific turbidity, K, are sinusoidal curves. It was noticed that, along one branch of the K-α curve (up to 1.1 μm for relative refractive indices (rr_l) <1.2), the wavelength dependence on turbidity; i.e. the extent to which light at different wavelengths is scattered showed a progressive decrease with increase in droplet diameter. It was in fact found that when the logarithm of the relative standard deviations (RSD's) in specific turbidities at four different wavelengths (for a particular droplet diameter and relative refractive index) was plotted as a function of that diameter, a straight line resulted. This relationship provides a valuable new method for estimating the surface volume mean droplet size, D_vs, for submicron emulsions by means of simple spectro-turbidimetry.