ABSTRACT
Dynamic light scattering (DLS) is widely used as an effective technique for determining the average size of Brownian nanoparticles in colloidal suspensions. In DLS, coherent light from an incident laser beam illuminates a liquid medium in which small particles are suspended. When the particle size is much smaller than the wavelength of light, the scattered radiation from the particles is in phase based on Rayleigh scattering. The resultant scattering pattern comprises scattering by individual particles as well as scattering by the wider many-particle system, which changes in time due to the Brownian motion. Therefore, time-dependent correlation functions are used in DLS measurements to provide information on how the dynamical properties of particles in the liquid phase are statistically correlated over a period of time. Using Stokes–Einstein assumption, the correlation could be interpreted as hydrodynamic size. In fact, there is a large number of commercial instruments and analytical methods based on various principles of DLS. In order to clarify the basic principles of DLS, which is important for accurate measurements by DLS user, the fundamental theory of DLS based on the photon correlation spectroscopic method is expounded in this chapter.
