The Determination of Refractive Indices of Colloidal Particles by Means of a New Mixture Rule or from Measurements of Light Scattering

Abstract

A new theoretical mixture rule is developed for determining the refractive index of colloidal particles from differential refractometric measurements. The new rule gives better results for colloidal solutions than the mixture rules of Newton, Lorenz-Lorentz, or Wiener if the difference between the refractive indices of the colloidal particles and of the medium is small. If the difference is large, but not in excess of 0.7, the refractive index of the particles can still be obtained with an accuracy in the third or fourth decimal by using an empirical correction equation. If colloidal solutions are very opaque, the refractive index of the particles can be calculated from light scattering. Application of the respective equation requires that the refractive index of the medium and the size of the particles are known. The gravimetric and volumetric measurements involved in the determination of density of colloidal particles can be replaced in part or entirely by measurements of light scattering and refractivity.