title: Dynamics of asymmetric binary glass formers. I. A dielectric and nuclear magnetic resonance spectroscopy study.
abstract: Dielectric spectroscopy as well as (2)H and (31)P nuclear magnetic resonance spectroscopy (NMR) are applied to probe the component dynamics of the binary glass former tripropyl phosphate (TPP)/polystyrene (PS/PS-d3) in the full concentration (cTPP) range. In addition, depolarized light scattering and differential scanning calorimetry experiments are performed. Two glass transition temperatures are found: Tg 1(cTPP) reflects PS dynamics and shows a monotonic plasticizer effect, while the lower Tg 2(cTPP) exhibits a maximum and is attributed to (faster) TPP dynamics, occurring in a slowly moving or immobilized PS matrix. Dielectric spectroscopy probing solely TPP identifies two different time scales, which are attributed to two sub-ensembles. One of them, again, shows fast TPP dynamics (α2-process), the other (α1-process) displays time constants identical with those of the slow PS matrix. Upon heating the α1-fraction of TPP decreases until above some temperature Tc only a single α2-population exists. Inversely, below Tc a fraction of the TPP molecules is trapped by the PS matrix. At low cTPP the α2-relaxation does not follow frequency-temperature superposition (FTS), instead it is governed by a temperature independent distribution of activation energies leading to correlation times which follow Arrhenius laws, i.e., the α2-relaxation resembles a secondary process. Yet, (31)P NMR demonstrates that it involves isotropic reorientations of TPP molecules within a slowly moving or rigid matrix of PS. At high cTPP the super-Arrhenius temperature dependence of τ2(T), as well as FTS are recovered, known as typical of the glass transition in neat systems.
authors: Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany.
authors: R
authors: R
authors: Kahlau
authors: Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany.
authors: D
authors: D
authors: Bock
authors: Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany.
authors: B
authors: B
authors: Schmidtke
authors: Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany.
authors: E A
authors: EA
authors: Rössler