Dispersion of depolarisation of light-scattering in colloids. Part V. Colloidal dye-stuffs

Abstract

The earlier work on the absorption of light by aqueous solutions of organic dye-stuffs has been briefly reviewed. It is pointed out that the study of the optical properties, especially the Tyndall effect, of colloidal dye-stuffs which can be obtained in suspension with the particles graded down from those of microscopic to those of molecular dimensions, is of great importance to understand the connection between the degree of dispersivity and kinetics of the dyeing processes. Measurements of the depolarisation factors ρ _u , ρ _v and ρ _h and the extinction coefficients of aqueous solutions of ten typical dye-stuffs are made for different wave-lengths from 2500 to 7000 A.U. As in the case of metallic sols, such as gold and silver, so also in the case of these dye-stuffs the depolarisation values attain their maximum value in the regions of specific absorption. The depolarisation measurements indicate that the sols of aniline blue, congo red, congo rubin and nigrosin contain anisotropic ultra-microscopic micellae whereas the solutions of indigotin, Hoffman's blue and iodine green are molecular and not colloidal. The solutions of methyl violet, chryosidine and orange II occupy an intermediate position.