How much light is scattered by a particle?
The particles that we size are generally in the Rayleigh or Rayleigh-Debye-Gans scattering regime. As an approximation briefly the Rayleigh regime will be discussed. In this case the efficiency of light scattering is given by: Therefore the factors affecting the amount of light scattered are: • d = the particle diameter. If you double the particle size you increase the power of light scattered by a factor of 64. • λ = the wavelength of light. If you half the wavelength of light you increase the scattering by a factor of 16. • n = the ratio of the particle refractive index to the solvent refractive index. For example for latex particles (ref. ind. 1.59) in water (ref. ind. 1.33), n is 1.195 and the factor is 0.0157. However for the case of gold (ref. ind. 0.2-3.37i) in water n is 0.15+ 2.53i and is 2.78, a factor of 177 greater than for the latex particles.
