Light scattering in the study of colloidal and macromolecular systems

Publisher Website
Google Scholar
Abstract
The fundamentals of the traditional (integrated) light scattering method are reviewed together with the application to a variety of macromolecules of both corpuscular and asymmetric form. Brief mention is made of the application of optical methods to the investigation of particles comparable and larger than the wavelength of the light and of much higher refractive index. Usually termed Mie theory, this involves complex calculations which, in modern instruments, are performed by built-in computers. For much larger particles, Fraunhofer diffraction is available, which can be applied for particle dimensions up to 700 μm. With the introduction of the laser, improvements in traditional light scattering became possible but more importantly, new possibilities arose which made use, particularly, of the coherence properties of laser radiation. Thus dynamic light scattering is concerned with the intensity fluctuations in time which arise from the various possible motions of the scattering particles. Special digital correlators have been introduced to measure the intensity correlation function as the delay time is varied over a large range of values. For spherical particles in dilute solution this gives accurate translational diffusion coefficients and a semi-quantitative measure of the polydispersity for a wide range of particle sizes (from enzymes to viruses). For rod-like particles, in favourable cases, a rotational diffusion coefficient may also be determined and in the case of flexible chain-like molecules, information on the lower order internal modes of vibration may be obtained. For motile micro-organisms, new features on the correlation decay yield a measure of their velocity distribution. All these fields are in active development.