Excess wing and Johari-Goldstein relaxation in binary glass formers

Dielectric loss spectra of pure quinaldine and tert-butylpyridine and their mixtures with tristyrene are presented. The pure systems present an excess wing and no secondary peaks in the temperature interval from above to well below the glass transition. However, when mixed in low concentration with tristyrene the excess wing is replaced by a distinct secondary peak. This distinct process can be identified as a Johari-Goldstein relaxation within the coupling model interpretation. In the frame of the coupling model the transition from the relaxation scenario with the excess wing to that with a distinct secondary peak is related to the increase of intermolecular constraints. In our case this increase of constraints is due to the low mobility component of the mixture (tristyrene).