TRANSLATION-ROTATION PARADOX FOR DIFFUSION IN FRAGILE GLASS-FORMING LIQUIDS - COMMENTS

F. H. Stillinger and J. A. Hodgdon [Phys. Rev. E 50, 2064 (1994)] have proposed a ''fluidized domain'' model to explain that the diffusion c oefficient ratio D-trans/D-rot increases by a factor of similar to 10( 2) on approaching the glass transition from above in fragile liquids. In their numerical estimates they make ad hoc assumptions that lead to a very small volume fraction phi(0) similar to 10(-5) of the fluidize d domains. It is shown how these assumptions can be avoided and phi(0) similar to 10(-1) results from experimental values of D-trans, D-rot, and the width of the D-rot distribution. A modification of the Stilli nger-Hodgdon model can be derived from the two-state model of Beckert and Pfeifer [Ann. Phys. (Leipzig) 16, 262 (1965)] and yields experimen tal estimates of a few nanometers for the fluidized domains.