Glass transition of polymers: Memory effects in structural relaxation of polystyrene

Two-Dimensional 109Ag NMR and Random-Walk Simulation Studies of Silver Dynamics in Glassy Silver Ion Conductors

“…However, deviations from the curve calculated for truly heterogeneous dynamics indicate that a significant number of forward-backward jumps takes place in the RBM and the REM as well. Altogether, the findings, in particular those for the RBM, are very similar to 2 H NMR three-time correlation functions measured for polystyrene near the glass transition temperature T g [18].…”

“…Here, we consider sin-sin correlation functions for a short evolution time t p ¼ 1 ms: In this case, the sine functions can be approximated by their argument and the correlation function of the NMR frequencies F 2 ðt m Þ / hoð0Þoðt m Þi is observed. To study the nature of the non-exponential relaxations resulting from the RBM and the REM, respectively, we compute NMR three-time correlation functions F 3 ðt m0 ; t m0 Þ: In experimental practice, F 3 ðt m0 ; t m0 Þ is recorded by applying a seven-pulse sequence known from the reduced four-dimensional (4D) NMR experiment [18,47,48]:…”

“…More insight into complex motional processes is available on the bases of three-and four-time correlation functions in NMR. For example, correlated forward-backward jumps which were often proposed to take place for polymer segments near the glass transition were proven to occur by analyzing three-time correlation functions [18]. Finally, when recording four-time correlation functions [2,19,20] the lifetime of dynamical heterogeneities can be measured.…”

Nuclear magnetic resonance and dielectric spectroscopy of a simple supercooled liquid: 2-methyl tetrahydrofuran

“…It should be noted that the NMR and the bleaching experiments are directly comparable since they were both carried out for polystyrene as well as for supercooled ortho-terphenyl. 4,10,16 The NMR measurements were also performed for many other glass formers, 17 including polyvinylacetate. 3,18 The latter polymer was additionally studied using polarization noise measurements.…”

Glass Transition Measurements of Ultrathin Polystyrene Films

“…Although there is agreement that near the substrate interface, the value of T g is shifted from the bulk due to confinement and size effects, there is evident contradiction in the direction of the shift. Problems such as local density variations normal to the interface, interfacial roughness, and film imperfections due to partial dewetting are listed as potential causes for these contradicting interpretations (21).…”