Photon correlation study of structural relaxations in NaCF3SO3 containing polymer electrolytes

Bergman, Rikard; Börjesson, Lars; Fytas, George; Torell, L. M.

doi:10.1016/0022-3093(94)90585-1

Cited by 22 publications

(15 citation statements)

References 17 publications

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“…Thus, the Na + –PVP interaction was reflected in small but significant shifts of relevant bands in the infrared spectrum (Figure S4). This is in line with observations on polymer electrolytes: for bulk polypropylene oxide (PPO)/NaCF 3 SO 3 electrolytes with the monomer/Na ratios of 30:1 and 16:1, the PPO T g upshift was about 9 and 19 K, respectively. , For the extremely confined monolayer hybrid Bragg stack with a 5:1 monomer/Na + ratio, the observed PVP T g increase (∼ 100 K) is, however, clearly much higher than that anticipated (∼ 60 K) based on such a polymer electrolyte effect. Either way, and regardless of quantitative considerations, the general trend of a slowdown is well known to be that for attractive (hydrophilic) interfaces .…”

Section: Results and Discussionsupporting

confidence: 89%

“…Hence, the most evident explanation to reconcile the XPCS and DS datasets is to associate them with two different relaxation processes in the polymer, as also reported for polyelectrolytes. 33,34 However, considering previous results, 15,16 these relaxation processes are most readily interpreted as pertaining to bulk-like (Figure 1d) and interface regions, with an abrupt transition between both that has been shown in simulations 53 to occur for certain polymers. The bulk-like process appears alongside the interfacial once the second PVP chain is introduced into the interlayer; however, this neat correspondence between the layer number and T g number is likely fortuitous.…”

Section: ■ Results and Discussionsupporting

confidence: 53%

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Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown

et al. 2021

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Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature T g close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of sample designs very specific to a single experiment. Here, we show how to translate results on confined thin film T g to a "nacre-mimetic" clay/polymer Bragg stack, where periodicity allows to limit and tune the number of polymer layers to either one or two. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard T g and broadband dynamic measurements. For the monolayer, we not only observe a dramatic increase in T g (∼ 100 K) but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics, originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both "bulk-like" and clay/polymer interface contributions, as manifested in two distinct T g processes. Because the platelet dynamics of monolayers and bilayers are similar, while the segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large T g shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions.

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Section: Results and Discussionsupporting

confidence: 89%

Section: ■ Results and Discussionsupporting

confidence: 53%

Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown

et al. 2021

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“…Since our first work 4 on this matter, Bergman et al 6 have reported two relaxation features in a photon correlation study on mixtures of NaCF 3 SO 3 with a M ) mixtures were biphasic at the microscopic level, they did not reexamine the Raman data previously reported by Schantz and Torell 7,8 on this system and on the PPO-LiClO 4 system. These data, which had been interpreted in terms of ion association by assuming full homogeneity, reveal that the anion environment remains unchanged from O/Na ) 16 to O/Na ) 1000 for NaCF 3 SO 3 and from O/Li ) 10 to O/Li ) 1000 for LiClO 4 .…”

Section: Introductionmentioning

confidence: 82%

Conductivity Behavior below and above the Critical Composition for Microphase Separation in Poly(propylene oxide)−Sodium Salt Electrolytes

et al. 1998

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This study, performed on mixtures of NaClO4 and NaCF3SO3 with atactic poly(propylene oxide) (PPO), confirms that a microphase separation phenomenon takes place in both low and high molecular weight PPO. Below a certain concentration, which corresponds to O/Na ) 13 (O ) ether oxygen) in a M ) 4 × 10 3 PPO and to O/Na ) 11 in a M ) 2 × 10 5 PPO, optically clear mixtures exhibit two glass transition (Tg) features indicating that a salt-rich microphase separates from the polymer. A comparison with poly(ethylene oxide) (PEO) amorphous mixtures containing the same salts shows that this phenomenon has a dramatic effect on ion conduction. It also reveals that an ion-entrapping structure, similar to that in the salt-rich microphase, is present over a range of concentrations above the critical composition. Although chain length has a marginal effect on conductivity in PEO, it has a strong effect on conductivity in PPO. As evidenced by a sharper Tg splitting in the high molecular weight PPO, this effect is due to the formation of larger microdomains. From this feature and the change in the microdomain composition, it may be argued that solvating power of PPO decreases with increasing chain length or decreasing OH end-group density.

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“…Only a single glass transition was observed for higher concentrations. In photon correlation studies , of poly(propylene glycol)/NaCF 3 SO 3 and poly(propylene glycol)/Mg(ClO 4 ) 2 , two structural relaxation processes clearly separated in time were observed. The slow process was attributed to segmental motion around cation transient cross-links, whereas the fast process was attributed to the motion of chain sequences away from the cross-links.…”

Section: Previous Studiesmentioning

confidence: 96%

Molecular Dynamics Simulations of Poly(ethylene oxide)/LiI Melts. 1. Structural and Conformational Properties

1998

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Molecular dynamics (MD) simulations of PEO/LiI melts at 363 and 450 K for the ether oxygen (EO)/LiI compositions 48:1, 15:1, and 5:1 have been performed. An explicit atom quantum-chemistry-based force field developed in our previous work was used. The Li+ cation environment from our MD simulations was found to be in good agreement with neutron diffraction isotopic substitution (NDIS) experiments performed on the EO/Li = 5:1 system. Cation complexation was found to be strongly temperature dependent. The Li+ cations have a tendency to be coordinated by six or more contiguous EO from a single chain at the lower temperature (363 K), but as temperature increases, coordination by shorter contiguous ether oxygen atom sequences becomes increasingly probable. The number of “free” ions was found to decrease with increasing temperature, consistent with results from Raman spectroscopy experiments on similar polymer electrolyte systems. The strong temperature dependence of the cation environment indicates the importance of entropic factors in cation complexation. In contrast to the strong temperature dependence, simulations revealed the local Li+ environment at 450 K to be nearly independent of salt concentration for systems more dilute than 15:1. In this dilute regime, the system forms salt-rich and pure PEO-like domains of size comparable to that of half of the simulation box. The Li+ cations strongly perturb the conformations of PEO compared to those of the pure melt but only locally. It was found that addition of salt leads to a decrease of the radius of gyration of PEO chains. This effect is more pronounced at lower temperature. At higher salt concentration, the Li+ cation environment becomes composition dependent, and the local heterogeneities begin to disappear.

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Photon correlation study of structural relaxations in NaCF3SO3 containing polymer electrolytes

Cited by 22 publications

References 17 publications

Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown

Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown

Conductivity Behavior below and above the Critical Composition for Microphase Separation in Poly(propylene oxide)−Sodium Salt Electrolytes

Molecular Dynamics Simulations of Poly(ethylene oxide)/LiI Melts. 1. Structural and Conformational Properties

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Photon correlation study of structural relaxations in NaCF3SO3 containing polymer electrolytes

Cited by 22 publications

References 17 publications

Large Tg Shift in Hybrid Bragg Stacks through Interfacial Slowdown

Large Tg Shift in Hybrid Bragg Stacks through Interfacial Slowdown

Conductivity Behavior below and above the Critical Composition for Microphase Separation in Poly(propylene oxide)−Sodium Salt Electrolytes

Molecular Dynamics Simulations of Poly(ethylene oxide)/LiI Melts. 1. Structural and Conformational Properties

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Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown

Large T_g Shift in Hybrid Bragg Stacks through Interfacial Slowdown