Calorimetric indications of a cooperativity onset in the crossover region of dynamic glass transition for benzoin isobutylether

Heat capacity spectroscopy (HCS), dielectric spectroscopy, and shear viscos ity data are reported for liquid benzoin isobutylether (BIBE). Dielectric a nd viscosity peculiarities indicate the crossover region of dynamic glass t ransition at T=(-8 +/- 8) degrees C where the extrapolated Johari Goldstein beta relaxation intersects the main transition trace in an Arrhenius plot. Although HCS does not reach the crossover frequency of order omega=2x10(6) rad/s, the linear decrease of the square root of cooperativity as calculat ed from HCS data at lower frequencies indicates a cooperativity onset in th e crossover temperature-frequency range. As BIBE belongs to another dielect ric crossover scenario as the substances where such an onset could previous ly be observed, it seems that the cooperativity onset is a general property of the crossover region. (C) 1999 American Institute of Physics. [S0021- 9 606(99)50938-0].