Is the Johari-Goldstein β-relaxation universal?

Mohamed Shahin Thayyil (1) , Simone Capaccioli (2) , Daniele Prevosto (3) , Kia Ling Ngai (4)

1 Dipartimento di Fisica
2 Physics
3 Department of Physics
4 Code 6807

The Johari-Goldstein (JG) β-relaxation is supposedly a universal feature in glassy dynamics and has strong connections to the structural α-relaxation in all glassformers. However, against the hypothesis of its universality are some greatly studied small molecular glassformers which give no indication that JG relaxation is present despite investigations using a variety of experimental techniques. These exceptions cast doubt on its universal nature and fundamental importance. Theoretical consideration suggests that the JG β-relaxation is present but not resolved in these glassformers because it is sandwiched between the more intense α- and a faster but non-JG secondary γ-relaxation. We investigate such suggestion on several glass formers and we report herein representative data on benzophenone and dimethyl phthalate. We show that by dissolving any of these glassformers in hosts with much higher glass transition temperatures, we were able to move the α-relaxation further away from the γ-relaxation, and find the JG β-relaxation for the first time in two glassformers of current interest in the research community.

Mots clés: Physical Sciences

Mohamed Shahin Thayyil, Simone Capaccioli, Daniele Prevosto, Kia Ling Ngai. Is the Johari-Goldstein β-relaxation universal?. Philosophical Magazine, 2008, 88 (33-35), pp.4007-4013. ⟨10.1080/14786430802270082⟩. ⟨hal-00513923⟩