It was noted that relaxation and diffusion in interacting systems, including most glass-forming substances, involved many-body dynamics. The stretch exponent, n, in the Kohlrasuch correlation function, φ(t) = exp[-(t/τα)1-n], was a convenient measure of the many-body relaxation dynamics. Evidence of the importance of many-body dynamics could be gleaned from the empirical facts that n either governed, or was correlated with, several general relaxation properties. One example of this was the aging of colloidal glasses. A second example was the breakdown of the Stokes-Einstein and Debye-Stokes-Einstein relationships in small molecular glass formers, colloidal particle suspensions and a Lennard-Jones system with a rotational degree of freedom. The coupling model involved a relationship in which n played a pivotal role in governing the relaxation properties.

The Vestige of Many-Body Dynamics in Relaxation of Glass-Forming Substances and Other Interacting Systems. K.L.Ngai: Philosophical Magazine, 2007, 87[3-5], 357-70