Light Scattering and Spinodal Decomposition in Glasses

It is shown that the well‐known anomalous Rayleigh scattering of phase‐separated glasses, which can be accounted for by the assumption of nucleation of a new phase followed by diffusion‐controlled growth, can also be qualitatively accounted for by the assumption that the phase separation is occurring within the spinodal region of the phase diagram; here there is no nucleation barrier to phase separation, only a diffusional barrier. A distinction between the two mechanisms in any actual system can be made only by the use of other experimental tools, such as electron microscopy. A quantitative theory of this process proposed by Cahn is examined; it is concluded that light scattering probably reveals only the later stages of the process, rather than the initial stages dealt with by Cahn's theory.