Dynamic Viscosity of a Simple Glass-Forming Liquid

We have measured the viscosity $\eta$ and the frequency-dependent shear modulus of the glass-forming liquid di-$\eta$-butylphthalate. Both $\eta$ and the shear relaxation time $\tau$ have non-Arrhenius dependence on temperature $T$. The ratio $\frac{\eta }{{\tau }^T}$ is weakly $T$ dependent implying a slight deviation from the Einstein-Debye equation. This is fully explained by a smooth evolution of the relaxation spectrum and is not accompanied by growth of the elastic shear modulus or a correlation length, as had been suggested.