Logarithmic decay of the orientational correlation function in supercooled liquids on the Ps to Ns time scale

Dynamics of supercooled ortho-terphenyl, salol, benzophenone, 2-biphenylmethanol, and dibutylphthalate have been studied using optical heterodyne detected optical Kerr effect experiments over a broad range of time, <1 ps to tens of ns. On time scales longer than those influenced by intramolecular vibrational dynamics, "intermediate" power law decays with temperature independent exponents close to -1 have been observed from similar to 2 ps to 1-10 ns in all five samples. The intermediate power law decays occur over a wide range of temperatures from well above to somewhat below T-c, the mode-coupling theory (MCT) critical temperature. The intermediate power law corresponds to approximately a logarithmic decay of the polarizability-polarizability (orientational) correlation function. The amplitude of the intermediate power law increases with increasing temperature as [(T-T-c)/T-c](1/2). The intermediate power law decay is followed by a second longer time scale power law, and the final portion of the decay is exponential. As a framework for discussion, the results are compared to the quantitative predictions of the MCT. The observations are in contrast to the standard MCT for the longer time portions of the decays. The observed intermediate power law decays may be consistent with MCT if the dynamics occur in the part of the MCT parameter space near a high order singularity (end point case). (C) 2003 American Institute of Physics.