Is the Johari-Goldstein β-relaxation universal?

The Johari-Goldstein (JG) β-relaxation is supposedly a universal feature of glassy dynamics and has strong connections to structural α-relaxation in all glass-formers. On the other hand, some small molecular glass-formers give no indication that JG relaxation is present, despite numerous investigations using a variety of experimental techniques. These exceptions cast doubt on universality and fundamental importance. Theoretical considerations suggest that the JG β-relaxation is present but unresolved in these glass-formers because it is sandwiched between the more intense α-relaxation and a faster, but non-JG, secondary γ-relaxation. We report representative data on two glass-formers, benzophenone and dimethyl phthalate. We show that by dissolving either glass-former in a host with a much higher glass transition temperature, we were able to move the α-relaxation further from the γ-relaxation. We also report, for the first time, JG β-relaxation in two glass-formers of current research interest.