TRANSLATIONAL AND ROTATIONAL MOLECULAR-MOTION IN SUPERCOOLED LIQUIDS STUDIED BY NMR AND FORCED RAYLEIGH-SCATTERING

It has been shown that translational diffusion coefficients, D-t, in t he supercooled van der Waals liquids, orthoterphenyl, phenolphthaleind imethylether, and salol, have a weaker temperature dependence than the shear viscosity, eta, at T less than or similar to 1.2 T-g and can be described by D-t similar to eta(-xi) with xi < 1, whereas D-r similar to eta(-1) applies for the mean rotational diffusion coefficients, D- r, down to the glass transition temperature, T-g. This apparent decoup ling of translational and rotational motion has been discussed in rela tion with possible anomalous short time diffusion, spatial heterogenei ty, and cooperative molecular motions close to T-g.