title: Picosecond dynamic heterogeneity, hopping, and Johari-Goldstein relaxation in glass-forming liquids.
abstract: We show that incoherent quasielastic neutron scattering from molecular liquids reveals a two-state dynamic heterogeneity on a 1 ps time scale, where molecules are either highly confined or are free to undergo relatively large excursions. Data ranging from deep in the glassy state to well above the melting point allows us to observe temperature-dependent population levels and exchange between these two states. A simple physical picture emerges from this data, combined with published work, that provides a mechanism for hopping and for the Johari-Goldstein (β_{JG}) relaxation, and allows us to accurately calculate the diffusion coefficient, D_{T}, and characteristic times for α, and β_{JG} relaxations from ps time scale neutron data.
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8543, USA and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Marcus T
authors.initials: MT
authors.lastname: Cicerone
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8543, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhong
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8543, USA and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Madhusudan
authors.initials: M
authors.lastname: Tyagi
mesh_terms: D005898:Glass / Q000737:chemistry*; D008956:Models, Chemical; D033363:Neutron Diffraction; D044367:Phase Transition; D013816:Thermodynamics