Optical behavior of organic pigments in aqueous dispersions and its application

The intensity of a beam of light on passing through a dilute pigment dispersion is attenuated as a result of absorption and scattering of light by the pigment particles. It was found that the particle size distribution of an organic pigment not only controls the light scattering but also affects the light absorption. As the milling time increases, the absorption coefficient increases while the scattering coefficient decreases. The peak-to-valley ratio obtained from the extinction spectra of the pigment dispersions can be used to determine the dispersion degree of organic pigments, and this method was confirmed by particle size measurements.