Intracrystalline Jump Motion in Poly(ethylene oxide) Lamellae of Variable Thickness: A Comparison of NMR Methods

Abstract

Helical jumps in poly­(ethylene oxide), which are the molecular processes underlying the intracrystalline chain diffusion, are studied on the microseconds to milliseconds time scale by means of NMR. Using a simple proton time-domain technique, a wide range of melt-crystallized morphologies is investigated ranging from extended-chain crystals of short chains to crystals with disordered fold surfaces of longer chains up to 190 kg/mol. From variable-temperature data we directly determine the Arrhenius activation parameters and find that the activation energy is always around 65 kJ/mol. At a given temperature, average correlation times vary from sample to sample over about 1 decade and increase approximately linearly with the lamellar thickness. The observed linear relation is reproduced by a generic Monte Carlo simulation model implementing a mechanism of diffusing defects. The experimental results are compared to 1D carbon-13 MAS exchange NMR (CODEX) and proton rotating-frame relaxation (R 1ρ) data, for which we highlight the challenges and significant bias effects arising from the significant distribution of correlation times. Effective spin-diffusion averaging of the proton R 1ρ demonstrates that monomers with different jump dynamics are spatially close; i.e., they coexist in neighboring stems.

Reduced-mobility layers with high internal mobility in poly(ethylene oxide)–silica nanocomposites

“…However, the values in Table II are almost 8 times smaller, indicating high internal mobility of the "rigid" component comparable in amplitude to what is expected and has been measured for a rotating backbone. 30 Notably, the DQ-filtered data exhibit a Gaussian shape with in some cases even a slight modulation associated with coherent spin dynamics. This suggests that this component is in the "quasi-static" fast limit, i.e., the associated correlation time is significantly below 1 µs (slower mobility leads to intermediate-motional effects and thus β exponent values below 2).…”

“…30 At temperatures below 70 • C, the crystalline and glassy amorphous components of PEO are indistinguishable, and from fits in this temperature range M 2 (T ) = [13 500 − T × (20 • C)] ms 2 was determined. This rather weak dependence mainly subsumes thermal expansion and small-angle libration effects, and we take this value as a reference.…”

Probing the Dynamics of Li+ Ions on the Crystal Surface: A Solid-State NMR Study

“…For example, most PEO/Li + complexes are semi-crystalline [23]. In semi-crystalline polymers, the crystallites are always surrounded by non-crystalline structures [24][25][26]. Such morphologies are also present in most PEO/Li + complexes.…”

Intracrystalline Dynamics in Oligomer‐Diluted Poly(Ethylene Oxide)

“…[9] Also the process of reversible surface melting and crystallization, and the correlated changes in the crystalline-amorphous interphase, which is reported for crystal-mobile polymers such as poly(ethylene oxide) (PEO), [10] is only feasible due to the intracrystalline dynamics in this polymer class. There is some evidence that jump-like monomer motions ("helical jumps") are mediated by localized and traveling conformational defects, [11][12][13][14][15][16] which are thus the elementary process of the intracrystalline chain diffusion.…”