Studies of the kinetics of nucleation and growth of pigment dispersions using a laser light-scattering apparatus in a flow system
The shape and size distribution of pigment particles affects their physical properties, in particular their hue. A continuous coupling flow system has been developed to determine and study the factors that influence particle shape and size during the production of azo-pigments. Information about the average particle size was obtained by measurement of the angular dependence of light scattered from a laser beam that passed radially through the flow tube. By this method the growth of the particles was monitored from the nucleation stage to the final particle size. An alternative to the Zimm plot method has been developed and used to analyse the light scattering data. The effects of particle concentration, shape and size distribution on the scattered intensities have been taken into account. The method has been applied to a study of the coupling of Toluidine Red (C.I. Pigment Red 3). The particle growth rate was found to decrease as the temperature was increased, and in each case the final particles were rod shaped and of similar size.
From these results it is deduced that the growth follows first order kinetics and the limiting size to which a particular nucleus can grow depends only on the concentration of precipitated molecules within a fixed volume surrounding the nucleus.