DEPOLARIZED-LIGHT-SCATTERING STUDY OF ORTHOTERPHENYL AND COMPARISON WITH THE MODE-COUPLING MODEL

The dynamics of the molecular glass-forming liquid orthoterphenyl above the glass-transition temperature was studied combining several experimental techniques: depolarized Raman, depo Rayleigh-Brillouin light scattering, and photon correlation spectroscopy in the temperature range from 250 to 440 K. The combined spectra covering a frequency range from 10(-2) to 10(13) Hz Were analyzed using the mode-coupling theory. The coordinates of the susceptibility minimum, omega(min) and chi(min), as well as the position of the maximum, omega(max) (alpha peak), scale with temperature according to the mode-coupling theory, resulting in T(c) = 290 K. The construction of the predicted master curve in the vicinity of the minimum of the rescaled susceptibility was possible in a narrow frequency range only if the values of omega(min) resulting from the mode-coupling-theory force fit were used. The width of the alpha peak appears to increase with increasing temperatures for temperatures above T(c), although when the effects of fast processes on the high-frequency wing are included, the corrected width appears to decrease instead approaching a Debye relaxation shape at high temperatures. Below T(c) it was not possible to fit objectively the data using the mode-coupling theory; thus it was impossible to corroborate the divergence of the scaling time of the mode-coupling beta relaxation on both sides of T(c). Assuming a priori that the mode-coupling model is correct, it is possible to make the data compatible with the mode-coupling theory.