Positron annihilation study of a low-molecular-weight organic glass-forming liquid (BMMPC)

¹ KFKI Atomic Energy Research Institute - 1525 Budapest, P.O.Box 49, Hungary
² Max-Planck-Institute of Polymer Research - Ackermannweg 10, 55128 Mainz, Germany
³ Institute of Physics, A. Mickiewicz University - Umultowska 85, 61614 Poznan, Poland
⁴ Department of Nuclear Chemistry, Loránd Eötvös University 1518 Budapest, P.O.Box 32, Hungary

Received: 25 January 1999
Accepted: 15 April 1999

Abstract

Positron lifetime spectra were obtained from 1,1-bis(paramethoxy-meta- methyl- phenyl)-cyclohexane (BMMPC) vs. temperature T between 23 and . At low temperatures, almost up to the glass transition at T_g, a fast pick-off annihilation mechanism is proposed for explaining the variations in the annihilation parameters of positronium (Ps). Above the Vogel temperature T₀ the lifetime of o-Ps is coherently interpreted in terms of a thermodynamic model which assumes the molecules to occupy solid- and liquid-like states. The transition temperature of the model calculated from o-Ps lifetimes is significantly less by than that obtained from all other physical quantities available, including free positron lifetimes.