Light Scattering and Spectrophotometry of Colloidal Solutions

Abstract

During the past several years it has been demonstrated that the light scattered from dilute solutions of macromolecules or colloidal particles is intimately related to the weight, size, and interaction of the solute species. Theoretical developments and improved techniques have made possible the determination of the molecular weight, dimension and activity coefficient of a number of polymers and proteins in solution. In these investigations the intensity of light scattered at various angles from a monochromatic beam passing through the solution has been measured by means of specially designed photometers. However, it would appear that the equivalent information could be derived from a different means of observation—that of transmission measurements at various wave‐lengths. If this possibility could be exploited the common techniques of spectrophotometry could replace the more specialized ones now used. The extent to which this is feasible is explored in this paper. As a first step it is necessary to review some aspects of the scattering from small particles and the internal interference arising in the case of larger particles. This opportunity is taken to present a compilation of the scattering factors and the quantities derived from them, that is the dissymmetry and correction factor, in a more precise and convenient form than has appeared previously, because of the use to which they are put in the following sections. The calculations relating to the case of transmittance of solutions containing larger particles are then presented and in the final sections the application of both methods of observation to the determination of the molecular weight and size of samples of polystyrene and tobacco mosaic virus is reported.