Ultrasonic investigation of the nematic-isotropic phase transition in MBBA.

Relaxation processes associated with the nematic-isotropic phase transition are investigated in liquid crystals of p-methoxybenzylidine-p-n-butylaniline. Sound velocity and absorption are measured at frequencies from 0.3 to 23 MHz at temperatures from 23 to 77 C in samples without preferred orientations. Particular attention is given to the region of transition at about 44 C. Sound absorption and velocity dispersion far from the phase transition region can be well described by a single relaxation process, while in the vicinity of the phase transition the acoustic properties are characteristic of a multiply relaxing fluid.