Physical interpretations of various dynamic light scattering data, their interconnections and relations to other relaxation data

Slow knot formation by suppressed self-reptation in a collapsed polymer chain

Chain-expansion processes from knotted globules have been measured for poly(methyl methacrylate) (PMMA) in the mixed solvent tert-butyl alcohol (TBA) + water (2.5 vol %) by static light scattering. The solution was quenched from the Θ temperature of 41.5 °C to 37.0 °C, aged there for a time period t(p,) and then returned rapidly to the Θ temperature. The chain-expansion process was determined as a time evolution of the expansion factor α(2) after the temperature increase. The measurement was carried out by changing the aging time t(p) from 240 to 7200 min, and the molecular weight from M(w) = 4.0 × 10(6) to 1.5 × 10(7), by taking advantage of the extremely slow chain aggregation in the solution. The chain-expansion process obtained for M(w) = 1.22 × 10(7) became slow with increasing t(p), which revealed the knot formation in single globules. The characteristic time of the chain expansion from globules aged for t(p) = 7200 min was found to depend on the molecular weight as M(w)(2.7). This exponent, which is close to 3, demonstrated a disentanglement process due to self-reptation. The present data were compared with the previous data of the chain expansion from compact globules aged at 25.0 °C. The comparison made at M(w) = 1.22 × 10(7) and at the same values of t(p) revealed that the chain expansion from the globules aged at 25.0 °C was much faster than that from the globules at 37.0  °C, indicating a lower knot density in the more compact globules. It was conjectured that the knot formation due to self-reptation would be suppressed in a compact globule because an entire conformational change required by knot formation would become difficult to occur in the confined space of high segment concentration, particularly for a long polymer chain. The chain collapse of PMMA in the mixed solvent has been observed to occur extremely slowly at the later stage. This slow process was explained by the suppressed self-reptation.

Broadband dielectric spectroscopy on glass-forming propylene carbonate

Dielectric spectroscopy covering more than 18 decades of frequency has been performed on propylene carbonate in its liquid and supercooled-liquid state. Using quasioptic submillimeter and far-infrared spectroscopy, the dielectric response was investigated up to frequencies well into the microscopic regime. We discuss the alpha process whose characteristic time scale is observed over 14 decades of frequency and the excess wing showing up at frequencies some three decades above the peak frequency. Special attention is given to the high-frequency response of the dielectric loss in the crossover regime between alpha peak and boson peak. Similar to our previous results in other glass-forming materials, we find evidence for additional processes in the crossover regime. However, significant differences concerning the spectral form at high frequencies are found. We compare our results to the susceptibilities obtained from light scattering and to the predictions of various models of the glass transition.