Particle-size determination by low-angle light scattering: effect of refractive index.

The intensity of scattering I(theta) by transparent and absorbing spheres has been calculated from exact Mie theory for values of radius from 0.1 microm to 100 ,microm, wavelength 5461 A, and the following values of refractive index m - im': (1) m = 1.01, 1.05, 1.1 (0.1) 2.0, m' = 0; (2) m = 2, m' = 0.002, 0.02, 0.2, and 2. The calculations have been made for a range of scattering angle theta large enough to indicate the first maximum in I(theta)theta(2). According to the Sloan method for determining particle radius, the location of this maximum is inversely proportional to radius, independent of refractive index. The exact calculations show that this is accurate for radii above 10 microm, but for smaller particles the value of the refractive index affects the location to some extent.