title: Correlation of positron annihilation and other dynamic properties in small molecule glass-forming substances.
abstract: Positron annihilation spectroscopy is used to characterize the ortho-positronium lifetime, tau(3), in a broad range of small molecule organic glasses over a wide temperature range. The magnitude and thermal variations of tau(3) reflect changes in the dielectric alpha-relaxation time tau(alpha) and its non-Arrhenius or "fragile" characteristics. tau(3) also displays striking similarities with the fast relaxations reflected in the hydrogen-weighted mean square atomic displacements <u(2)>. The parallel temperature variations of <u(2)(T/T(g))>, tau(3)(T/T(g)), and tau(alpha)(T/T(g)), and their similar patterns of change between the different glasses, are discussed in terms of anharmonicity in the intermolecular caging potentials and the subnanometer density heterogeneities.
authors.affiliation: Naval Research Laboratory, Washington, DC 20375-5320, USA.
authors.forename: K L
authors.initials: KL
authors.lastname: Ngai
authors.forename: L R
authors.initials: LR
authors.lastname: Bao
authors.forename: A F
authors.initials: AF
authors.lastname: Yee
authors.forename: C L
authors.initials: CL
authors.lastname: Soles