Homodyne light beating spectroscopy ofohyphen;terphenyl in the supercooled liquid state

摘要

The laser light scattering intensity fluctuations of supercooled liquidohyphen;terphenyl at temperatures between 12 and minus;15thinsp;deg;C have been studied using the photonhyphen;correlation technique. The time correlation functions obtained using the VV and VH scattering configurations at 90deg; scattering angle show a wide distribution of relaxation times. Angularhyphen;dependent measurements at 45deg;, 90deg; and 135deg; scattering angles show that the time correlation functions for VH and for VV are independent of scattering angles. The VV and VH correlation functions cannot be fit to a bimodal distribution function; neither can they be fit to a cumulant expansion expression with less than four cumulants, but they can be satisfactorily fit to the Williamndash;Watts distribution function. The mean relaxation times derived for both isotropic and anisotropic scattering processes from the VV and VH correlation functions are nearly equal. The temperature dependence of the relaxation times cannot be described by an Arrhenius equation with a constant activation energy. The average orientational relaxation times change by more than ten orders of magnitude in the temperature range between 147 and minus;16thinsp;deg;C but the temperature dependence of the orientational relaxation times over this wide dynamic range can be excellently correlated with the modified Debyendash;Stokesndash;Einstein equation. The closeness of the mean orientational relaxation time to the mean structural relaxation time is interpreted as due to strong rotationndash;translation coupling in the viscoelastic state. It is found that within the dynamic range of the autocorrelator, the collective shear wave plays no role in the time dependence of the VV and VH correlation functions. Quentrecrsquo;s theory of viscoelasticity based on the coupling of the shear wave to local translational order and orientational order is found to disagree with the experimental result. Comparison with the dielectric relation time data shows that inohyphen;terphenyl the dielectric relaxation and the present light beating techniques probe different types of motions.