Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)

Abstract

The electronic spectrum of SiH4: Jahn-Teller Rydberg series J. Chem. Phys. 135, 214304 (2011) Electronic states of tetrahydrofuran molecules studied by electron collisions J. Chem. Phys. 135, 134317 (2011) Dyson orbitals of N2O: Electron momentum spectroscopy and symmetry adapted cluster-configuration interaction calculations J. Chem. Phys. 134, 204304 (2011) Electronic excitations of potassium intercalated manganese phthalocyanine investigated by electron energy-loss spectroscopy J. Chem. Phys. 134, 194504 (2011) Experimental and theoretical study on generalized oscillator strengths of the valence-shell electronic excitations in CF4 J. Chem. Phys. 134, 064307 (2011) Additional information on J. Chem. Phys. We report a joint analysis of positron annihilation lifetime spectroscopy (PALS), dielectric spectroscopy (BDS), and nuclear magnetic resonance (NMR) on cis-trans-1,4-poly(butadiene) (c-t-1, 4-PBD). Phenomenological analysis of the orthopositronium lifetime τ 3 − T dependence by linear fitting reveals four characteristic PALS temperatures:. Slight bend effects in the glassy and supercooled liquid states are related to the fast or slow secondary β process, from neutron scattering, respectively, the latter being connected with the trans-isomers. In addition, the first bend effect in the supercooled liquid coincides with a deviation of the slow effective secondary β eff relaxation related to the cis-isomers from low-T Arrhenius behavior to non-Arrhenius one and correlates with the onset of the primary α process from BDS. The second plateau effect in the liquid state occurs when τ 3 becomes commensurable with the structural relaxation time τ α (T b2 ). It is also approximately related to its crossover from non-Arrhenius to Arrhenius regime in the combined BDS and NMR data. Finally, the combined BDS and NMR structural relaxation data, when analyzed in terms of the two-order parameter (TOP) model, suggest the influence of solidlike domains on both the annihilation behavior and the local and segmental chain mobility in the supercooled liquid. All these findings indicate the influence of the dynamic heterogeneity in both the primary and secondary relaxations due to the cis-trans isomerism in c-t-1,4-PBD and their impact into the PALS response.

A nano-scale free volume perspective on the glass transition of supercooled water in confinement

“…In both cases, our data are in excellent agreement with previously reported PALS measurements for glycerol [42,47]. The observed temperature dependence of the o-Ps lifetime measured for bulk reflects the typical behaviour of molecular glass formers as they pass through their glass transition [43][44][45][46][47][48][49]. Three characteristic temperatures can be identified in the thermal response of τ − o Ps measured in bulk glycerol, which according to previously described notation can be identified as T g,PALS , T b with increasing temperature mirrors the thermal expansion of the local free volume in the glassy matrix due to the anharmonicity of the molecular vibrations.…”

“…PALS is a well established technique extensively used for the study of local free volume and dynamics in a wide range of glass-forming systems, from simple liquids to synthetic polymers [37][38][39][40][41]. Over the past decade, PALS has been successfully used to study a variety of simple molecular glass formers both, in confinement [42] and in bulk [43][44][45][46][47][48][49]. Such studies have shown that model-free analysis of the temperature dependence of the orthopositronium (o-Ps) lifetime, τ − o Ps (reflecting the local free volume) reveals the existence of several characteristic temperatures [44,47,48].…”

Rethinking the Analysis of the Linear Viscoelastic Behavior of an Epoxy Polymer near and above the Glass Transition

“…Second, the strength of a dipole is a very weak function of temperature and, thus, cannot account for the temperature dependence of the peak height in ε″(ω) response that would be similar to that seen in the G ″(ω) isotherms shown in Figure . Although the current study has not reported on the dielectric behavior due to parasitic conduction and electrode polarization effects (see the Supporting Information), similar dielectric effects are reported for many glass-forming materials, ,,,,− which are also present for this DGEBA-MDA epoxy resins for temperature below T g that will be reported in a future publication.…”

Origin of the crossover in dynamics of the sub-Rouse modes at the same temperature as the structural α-relaxation in polymers

“…Remarkably, T PALS is nearly the same as T B from dielectric and mechanical data of s a , as shown by the s 3 data as a function of temperature of three small molecular glassformers, ortho-terphenyl (OTP), propylene carbonate (PC), and glycerol, [64][65][66] and polymers. [67][68][69] The coincidence suggests that the crossover of T-dependence of s a at T B bears some connection to the corresponding change of T-dependence of free volume at or near the same temperature. The more rapid decrease in free volume with temperature on crossing T B from above implies the corresponding more rapid increase of intermolecular coupling, which is consistent with the observed change in the T- of the coupling parameter n(T) in eqn (4).…”