Why do suspensions scatter light but solutions do not?
If an object is comparable to the wavelength of light usually strong scattering occurs — it is called Mie scattering. Since suspensions usually contain such kind of objects it is the reason they scatter light. On the other hand, there’s limit if Mie scattering, when the particle (or an arbitrary object) is much smaller than the wavelength of light — this limit is called Rayleigh scattering. The smaller becomes the particle the less amount of light is scattered. Here are some numbers: Say the wavelength of visible light is 550 nanometers (it’s greenish yellow). Suspensions may contain particles from 100 nanometers to several micrometers, that is, comparable to the wavelength. In solutions, single molecules are the objects light is scattered on, and their size is about 0.1 nm, which is 5000 times less than a wavelength of the visible light so weak Rayleigh scattering occurs.
