Shear viscosity and diffusion in supercooled liquids

Under normal liquid conditions (at equilibrium or when moderately supercooled), molecular rotational and translational diffusion adhere closely to the simple Stokes-Einstein-Debye hydrodynamic model. Deeply supercooled ''fragile'' liquids present a striking exception, with translational diffusion alone occurring up to 10(2) - 10(3) times ''too fast''. This anomaly rests upon the statistics of fluctuating local viscosity in the fragile glass-forming medium. The simplest version of this picture identifies large fluidized domains that spontaneously appear and disappear in a dynamically inert matrix. Plausible and self-consistent values characterizing these fluctuations are cited for orthoterphenyl (OTP) at its glass transition.