TEMPERATURE-DEPENDENCE OF THE STATIC STRUCTURE FACTOR OF ORTHO-TERPHENYL IN THE SUPERCOOLED LIQUID REGIME CLOSE TO THE GLASS-TRANSITION

Studying the temperature dependence of the static structure factor of ortho-terphenyl from the liquid state down to the glass we find that the main peak of S(Q) is split into two maxima which behave quite differently. While the maximum at Q = 1.4 angstrom-1 is not much affected by the temperature variation the one at 1.9 angstrom-1 is significantly enhanced. This effect is connected with a change of the short range order, i.e. of the intermolecular distances, but evolves continuously. Thus the dynamic anomalies that have been observed in this system around a characteristic temperature T(c) almost-equal-to 290 K are not simply due to a discontinuous change in S(Q) but can be attributed to the existence of a critical singularity in the dynamical behaviour at T(c) as predicted by mode coupling theory.