Network viscoelastic behavior in poly(ethylene oxide) melts: Effects of temperature and dissolved LiClO4 on network structure and dynamic behavior

Abstract

The ''wet gel'' model used earlier to describe the results of dynamic light scattering studies of neat poly͑ethylene oxide͒ ͑PEO͒ melts has now been successfully applied to PEO-melt/LiClO 4 solutions. The results of static light scattering and viscometry measurements along with measurements from dynamic light scattering revealed that with or without salt, the melt/gel was an overdamped system whose network diffusive relaxations were controlled by the damping liquid component of the gel. Important features of the melt/gel were significantly affected by the addition of LiClO 4 . Examples of important changes included increases in the network mesh size even as ''petrification'' of the network by the salt rendered it less elastic. Nevertheless, for 1 K PEO melts the essential nature of the melt/gel remained uneffected.

Molecular dynamics simulation of the polymer electrolyte poly(ethylene oxide)/LiClO4. II. Dynamical properties

“…On a microscopic view, PEO/ LiClO 4 dynamics has been revealed by NMR, 20 light scattering, 42 and quasielastic neutron scattering spectroscopy. 9 It will be shown that the united atom model for PEO is a reasonable one concerning dynamical properties with proper to good agreement between experimental and calculated intermediate scattering functions F͑k , t͒.…”

An investigation of a sol-gel/melt transition: The poly(ethylene oxide)/methanol/LiClO4 system

“…However, the small but persistent reduction in both ␤ f ͑particularly for lower polymer concentrations͒ and ␤ s ͑particularly for higher polymer concentrations͒ evident with increasing X is attributed to the effects of salt bridging on the polymer network. Alterations in the network structure because of bridging, behavior observed earlier in 1K PEO melts, 18 …”

“…This result can be compared with that for 1K PEO melts, where ⌫ decreased by roughly a factor of 20 over the same salt concentration range. 18 In the relatively unconstrained environment of the unentangled 1K PEO melt, the effect of added salt on long-ranged relaxations was less than in the more constrained environment of the highly entangled 50K PEO melt.…”

“…Based on rheological measurements, the critical value for the entanglement molar mass in PEO melts is about 3500. 26 After receipt from a Polymer Source, additional PEO purification was carried out as described earlier 18 and the final solution preparation conducted in a stainless steel glove box ͑Labconco, Kansas City, MO͒ filled with purified and dried nitrogen. The moisture level in the box was maintained below 10 ppm V ͑ten parts per million, by volume͒.…”

“…As for 1K PEO melts studied earlier, 18 static correlation lengths s s were extracted from static light scattering measurements of PEO solutions using the Ornstein-Zernike expression. However, because of the large magnitudes of s s values resulting from these fits, the condition q s s Ӷ1 was generally not satisfied and the static light scattering results provide, at best, rough approximations of s s .…”