Theoretical Investigations on the Light Scattering of Colloidal Spheres. V. Forward Scattering

The scattering of light, by nonabsorbing colloidal spheres, in the direction of the primary beam (forward direction), is calculated by means of the Mie theory as a function of α and m. The parameters considered are: α=1(1)15 for m=1.05(0.05)1.30 and, in addition, α=0.2(0.2)15.2 for m=1.20. In addition to the i values, the experimentally important quantity, I180/I0c, obtainable by Zimm plots, is evaluated. Its variation with particle size is compared to that of the total turbidity. The performance of the hitherto almost exclusively used Rayleigh-Gans-Debye equation is tested quantitatively against the exact Mie data. The advantages of the ``forward scattering method'' for determining particle sizes are enumerated and a series of desirable definitions and clarifications of angular light scattering quantities are included.