REFRACTION BY SPHERICAL COLLOID PARTICLES

The refraction of a dilute dispersion of nonabsorbing spherical particles is discussed on a light-scattering basis. The refraction of spheres is calculated using the exact Mie theory and the Rayleigh, Rayleigh-Gans, and Anomalous Diffraction approximations. In contrast to the strong particle size dependence of extinction, the refraction of small spheres is almost independent of sphere diameter. However, the refraction for larger, wavelength-sized particles varies in a complicated way with the sphere diameter. As also found for extinction, the Anomalous Diffraction approximation provides the closest fit to the Mie theory over the complete range of particle size and relative refractive index. For very large particles the complex extinction efficiency Qext = 2, while for these particles the complex refraction efficiency Pext = 0. The theory enables the particle size and its relative refractive index to be obtained from measurements of the extinction and refraction of spherical particle colloidal dispersions. © 1979 Academic Press, Inc.