THE DYNAMIC GLASS-TRANSITION OF A FRAGILE MOLECULAR LIQUID IN THE MEGAHERTZ DOMAIN

We have performed measurements of acoustic attenuation and sound velocity at ultrasonic frequencies in a molecular liquid (m-fluoroaniline) across its calorimetric glass transition T(g). This liquid offers the opportunity to observe its dynamical response continuously over an extended temperature domain where no crystallization is to be feared. The temperature dependence of the longitudinal moduli components M'(T) and M''(T) were derived and analysed with the Cole-Davidson and the Kohlrausch-Williams-Watts functions where a Vogel-Fulcher-Tamman expression and a power law were employed to link the main relaxation time to the temperature. The experimental behaviour of this molecular liquid is related to its 'fragile' character.