Dynamics Of PEO Research Articles

(Invited) Ion Transport and Interface Resistance in Polymer-Based Composite Electrolytes and Composite Cathode

Solid-state electrolytes are promising to enable the next generation batteries with higher energy density and improved safety. However, each major class of solid electrolytes has intrinsic weaknesses. By combining different classes of solid electrolytes, such as a polymer electrolyte and an oxide ceramic electrolyte, one can potentially overcome the intrinsic weaknesses of each component and develop a composite electrolyte to achieve high ionic conductivity, good mechanical properties, good chemical stability, and adhesion with the electrodes.In this presentation, we show that the interfacial resistance strongly affects the ionic conductivity of polymer/oxide ceramic composite electrolytes, in both the ceramic-in-polymer design where ceramic particles are dispersed within the polymer electrolyte matrix as well as the polymer-in-ceramic design where a three dimensionally interconnected ceramic scaffold is developed. The quantification of the interfacial resistance, the origin of this resistance, as well as the strategies to minimize it are discussed.In a second case, we examine the effect of interfaces on ion transport in a polymer based composite cathode consisting of LiFePO4 (LFP), carbon and poly(ethylene oxide) (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The structure and dynamics of PEO and lithium ion mobility are studied by small angle neutron scattering and quasi-elastic neutron scattering. The results show that Li ion mobility in PEO/LiTFSI in the composite cathode is only 30% of the bulk electrolyte. This suggests a key bottleneck that limits the rate performance of polymer-based solid-state batteries originates from the sluggish ion transport in the polymer electrolyte confined in the cathode.

Ion Transport Mechanism in Polymer Electrolytes - Bridging the Scales Via Molecular Simulations and Theory

Solid polymer electrolytes (SPEs) consisting of a salt in a polymer matrix are considered as safe alternatives to liquid electrolytes. However, at ambient temperatures, their conductivity is still too low for an efficient use in modern energy storages. To overcome this deficiency, several strategies have been proposed. For instance, it was demonstrated that the addition of a low-molecular-weight additive such as an ionic liquid (IL) results in improved transport properties [1]. To unravel the mechanisms how the ion transport is enhanced at the molecular level, molecular dynamics (MD) simulations are an extremely powerful tool. In case of classical SPEs based on poly(ethylene oxide) (PEO), three different microscopic transport mechanisms can generally be identified from MD simulations [2]: First, diffusion of coordinating lithium ions along the PEO backbone, second, cooperative motion of the ions with the PEO dynamics, and third, ion transfer processes between distinct PEO chains (see sketch). However, due to the limited size of the simulation system (in particular the length of the polymer chains), the comparison between experiments and the numerical data alone can be made only qualitatively. To bridge the gap between the different length and time scales characteristic for experiments and simulations, we devised an analytical framework based on polymer theory that allows us to extrapolate the numerical data to experimental scales. To illustrate this concept, we demonstrate that the way in which an IL may enhance the lithium mobility can in principle be twofold: First, the IL can act as a plasticizer, enhancing the dynamics of the polymer segments and thus also the motion of the attached lithium ions [3,4], and second, for specifically designed IL molecules that directly coordinate to the lithium ions (such as pyrrolidinium ions with chemically bound oligoether chains [5]), the IL may serve as a molecular shuttle detaching the lithium ions from the slow polymer chains [6], resulting in a much larger enhancement of the lithium ion transport. In a second step, we focus on SPEs based on diblock copolymers, consisting of a mechanically stable block and an ionically conducting PEO domain. Due to their increased overall rigidity, these electrolytes tend to suppress dendrite growth more efficiently, and thus are considered to be key candidates for lithium metal batteries. Special emphasis is again placed on the role of low-molecular-weight additives that recently have been studied experimentally [7], and on their impact on the molecular transport mechanism. [1] M. Joost, M. Kunze, S. Jeong, M. Schönhoff, M. Winter, S. Passerini, Electrochim. Acta 2012, 86, 330-338[2] D. Diddens, A. Heuer, O. Borodin, Macromolecules 2010, 43(4), 2028-2036[3] D. Diddens, A. Heuer, ACS Macro Lett. 2013, 2(4), 322-326[4] D. Diddens, A. Heuer, J. Phys. Chem. B 2014, 118(4), 1113-1125[5] J. von Zamory, G. A. Giffin, S. Jeremias, F. Castiglione, A. Mele, E. Paillard, S. Passerini, Phys. Chem. Chem. Phys. 2016, 18(31) 21539-21547[6] D. Diddens, E. Paillard, A. Heuer, J. Electrochem. Soc. 2017, 164(11), E3225-E3231[7] T. S. Dörr, A. Pelz, P. Zhang, T. Kraus, M. Winter, H.-D. Wiemhöfer, Chem. Eur. J. 2018, 24(32), 8061-8065 Figure 1

Polymer Compositional Ratio-Dependent Morphology, Crystallinity, Dielectric Dispersion, Structural Dynamics, and Electrical Conductivity of PVDF/PEO Blend Films

The polymer blend (PB) films consisted of poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO) with different compositional ratios (i.e., PVDF/PEO =100/0, 75/25, 50/50, 25/75, and 0/100 wt%) have been prepared by solution casting method. These PB films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and dielectric relaxation spectroscopy (DRS). The pristine films of PVDF and PEO have spherulite morphologies, which change enormously with the variation of their compositions in blend films. The EDX spectra confirm the linear variation of the amount of respective polymer elements, with the change of its compositional ratio in the PB films. The XRD and FTIR results confirm that the semicrystalline PVDF film has predominantly α- and β-phase crystals. The degree of crystallinity of these PB films exhibits non-linear increase, with increasing amount of PEO in the films. The relative fraction of the β-phase crystal of the PVDF in these complex PB films has been determined from the fractional relations based on the areas and intensities of crystalline peaks, observed in their XRD patterns which is found the maximum (~50%) for the 75 PVDF/25 PEO blend film. The dielectric dispersion of these PB films in the frequency window of 20 Hz-1MHz at 27 °C reveals that the real part of the complex permittivity is governed predominantly by the interfacial polarization effect at lower audio frequencies, whereas it mainly depends on the polymer compositional ratio at higher radio frequencies. The segmental relaxation process peak of the PEO chain observed in the loss part of the electric modulus spectra, shifts toward the lower frequency side with a significant suppression of intensity as the amount of PVDF enhances in the PB films. This result confirms that the PEO dynamics face considerable hindrance by the PVDF structures. The dc electrical conductivity of these PB films increases non-linearly with increasing amount of PEO in the films, and varies by more than an order of magnitude with the variation of the compositional ratio over the entire range. The temperature-dependent study of 50 PVDF/50 PEO blend film confirms its thermally activated dielectric properties and the structural dynamics with the relaxation activation energy of 0.23 eV. The compositional ratio-dependent dielectric properties of PVDF/PEO blend films offer a promising potential for their use as dielectric permittivity- and electrical conductivity-tunable insulating materials, with engineered functionality for flexible electronics and electrical devices.

Nonlinear optical and dielectric properties of TiO2 nanoparticles incorporated PEO/PVP blend matrix based multifunctional polymer nanocomposites

Poly(ethylene oxide) (PEO)/poly(vinyl pyrrolidone) (PVP) blend (50/50 wt%) and mixed-phase (anatase and rutile) titanium dioxide (TiO2) nanoparticles are used as organic host matrix and inorganic nanofiller, respectively, for the preparation of hybrid polymer nanocomposite (PNC) films (i.e. (PEO/PVP)–x wt% TiO2; x = 0, 1, 3, 5, 10, and 15) by solution casting method with deionized water as solvent. These PNC films are characterized by employing SEM, FTIR, XRD, UV–Vis, DSC, and DRS techniques. The effect of TiO2 nanofiller loading on the structural, morphological, thermal, optical, dielectric, and electrical properties of the PEO/PVP blend matrix, and also on the chain segmental dynamics of PEO in the PNC structures is investigated. It is revealed that the crystalline phase and spherulite morphology of PEO, and the polymer–polymer interactions in these PNC films have been primarily modified by the polymer–nanoparticle interactions. The optical energy band gap decreases, whereas UV absorbance enhances non-linearly with the increase of TiO2 concentration in the PNC films. The enthalpy of melting of the PEO irregularly reduces when the incorporated amount of TiO2 enhances in these films. The real part of complex permittivity and the dielectric loss tangent of these materials are found frequency independent in the range from 20 kHz to 1 MHz but these parameters increase non-linearly from ~ 1.6 to 2 and 0.006–0.008, respectively with the increase of TiO2 concentration up to 10 wt%, at 30 °C. The dominant contribution of interfacial polarization process increases the real part of complex permittivity of these PNC materials by about 1.3 times with the decrease of frequency from 20 kHz to 20 Hz which further enhances with the increment in the temperature of the film. The electrical behaviour of these materials has been examined by analyzing their ac electrical conductivity, complex impedance, and electric modulus spectra over the frequency range 20 Hz–1 MHz. The dc electrical conductivity of these PNC materials enhances nonlinearly with the increase of TiO2 loading in the PEO/PVP blend matrix. The optical and dielectric parameters of these flexible-type PNC materials confirm their multifunctional properties as UV absorber, optical energy band gap tuner, low permittivity tunable nanodielectric, electrical conductivity regulator, and novel host matrix for ion conducting materials. The results infer that these innovative technologically advanced engineered materials can be potential candidates for the next generation microelectronic devices.

Dynamics and Structure of Poly(ethylene oxide) Intercalated in the Nanopores of Resorcinol–Formaldehyde Resin Nanoparticles

The incorporation of high-molecular-weight poly(ethylene oxide) (PEO) in the nanopores of resorcinol–formaldehyde resin nanoparticles (RNPs) leads to the suppression of polymer crystallization, changes in the chain conformation, and a noticeable slowdown of the two dielectric relaxations that reflect the segmental and local PEO dynamics. Both relaxations are significantly slower than those corresponding to bulk PEO. These results are independent of the pore characteristics of the different RNP materials. The segmental relaxation shows a crossover at ca. 220 K in its temperature dependence from non-Arrhenius to Arrhenius-like behavior on cooling. These results suggest the occurrence of limited cooperativity at low temperatures due to the enhancement of long-living hydrogen bonding between PEO and RNP pore walls.

Interplay of Surface Chemistry and Ion Content in Nanoparticle-Filled Solid Polymer Electrolytes

We investigate the influence of nanofiller surface chemistry and ion content on the conductivity of nanofilled PEO + LiClO4 solid polymer electrolytes (SPEs) using dielectric spectroscopy, differential scanning calorimetry (DSC), FESEM, and quasi-elastic neutron scattering (QENS). We consider the concentration series EO/Li = 8:1, 10:1 (eutectic composition), 14:1, with both acidic α-Al2O3 and neutral γ-Al2O3 nanoparticles. The acidic filler is more effective at increasing conductivity at the non- eutectic compositions. In contrast, the two surface chemistries provide comparable increases at the eutectic composition. This composition maximizes the influence of nanofillers, regardless of surface chemistry. We find no significant changes in crystallinity, glass transition temperature, nanoparticle dispersion, or PEO segmental dynamics as a function of surface chemistry. In the absence of salt, acidic particles slow PEO dynamics more than neutral particles, suggesting that the PEO chains and the acidic surfac...

Investigation of a Nanocomposite of 75 wt % Poly(methyl methacrylate) Nanoparticles with 25 wt % Poly(ethylene oxide) Linear Chains: A Quasielatic Neutron Scattering, Calorimetric, and WAXS Study

We have investigated the thermal behavior, local structure, and dynamics in a system where 25 wt % PEO [poly(ethylene oxide)] linear chains are mixed with 75 wt % PMMA [poly(methyl methacrylate)] soft nanoparticles. Calorimetric and wide-angle X-ray scattering experiments point to a weak penetration of the PEO chains in the nanoparticles, qualifying the mixture as a nanocomposite. Quasi-elastic neutron scattering (QENS) experiments on partially deuterated samples has selectively revealed the component dynamics in the system. The α-methyl group dynamics of PMMA, which fall within the QENS time scale in the temperature range investigated, are hardly affected by the presence of PEO except for hints of a more heterogeneous environment in the nanocomposite than in bulk PMMA. The effects on the dynamics of PEO are more interesting. The observation of dynamics in the microseconds range for the PEO component of the nanocomposite at temperatures at which the calorimetric experiments indicate the freezing of its segmental relaxation provides evidence for confined dynamics below the main glass transition of the mixture—attributable to the effective glass transition of the slow component. A parallel study on an equivalent blend of PEO and linear PMMA chains shows that these effects are independent of the topology of the PMMA. However, well above the effective glass transition of the slow component, the dynamics of PEO differ in both systems. In the linear blend, PEO segments move with the typical features of supercooled polymers in metastable equilibrium, while in the nanocomposite PEO dynamics exhibit an anomalously strong deviation from Gaussian behavior. This deviation grows with increased mobility of the nanoparticles. PEO segments are seemingly trapped in effective cages imposed by the nanoparticles for a very long time—more than 2 orders of magnitude longer than in bulk or when surrounded by linear PMMA chains—before the subdiffusive process leading to segmental relaxation sets in. We speculate that local loops in the surface of the nanoparticles may play an important role in this trapping mechanism.

A comparison of effect of PEG and EC plasticizers on relaxation dynamics of PEO–PMMA–AgNO3 polymer blends

In the present study, Ag+-ion conducting polyethylene oxide–polymethyl methacrylate based polymer blend electrolyte systems plasticized using different plasticizers, i.e., ethylene carbonate and polyethylene glycol, are reported. The polymer films were synthesized using the solution cast technique and characterized by differential scanning calorimetry technique. Electrical properties of polymer films were investigated by impedance spectroscopy in the frequency range of 2 MHz–10 Hz at temperature range from 303 to 373 K. Discussion of electrical properties of polymer films in the terms of conductivity and relaxation times is made.

Single Chain Dynamic Structure Factor of Poly(ethylene oxide) in Dynamically Asymmetric Blends with Poly(methyl methacrylate). Neutron Scattering and Molecular Dynamics Simulations

We have investigated the dynamically asymmetric polymer blend composed of short (Mn ≈ 2 kg/mol) poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) chains focusing on the collective dynamics of the fast PEO component. Using neutron spin-echo (NSE) spectroscopy, the single chain dynamic structure factor of PEO was investigated and compared to results from molecular dynamics simulations. After a successful validation of the simulations, a thorough analysis of the RPA approximation reveals the composition of the experimentally measured total scattering signal S(Q,t). Using the simulations, we show and calculate two contributions: (1) the relaxation of hydrogenated PEO against deuterated PEO, yielding the single chain dynamic structure factor of PEO, and (2) the relaxation of the PEO component against the PMMA matrix. For the short chains presented here the second contribution shows a significant decay at higher temperatures while it was previously shown that, in the case of long chains, no relaxation is found. This difference is related to a decrease of the glass transition temperature which takes place with decreasing chain length. In a second step we analyze the approximations that are used when calculating the single chain dynamic structure factor using the Rouse model. For a system like pure PEO, where the dynamics follow the predicted Rouse behavior, excellent agreement is achieved. In the case of PEO in PMMA, however, the slow PMMA matrix strongly influences the PEO dynamics. As a result, the distribution functions show a strong non-Gaussianity, and the calculation of S(Q,t) using the Rouse approximation fails even considering nonexponential Rouse mode correlators.

Segmental Dynamics of Dilute Poly(ethylene oxide) in Low and High Molecular Weight Glass-Formers

Deuterium NMR at Larmor frequencies of 15.6 and 76.7 MHz was used to study the segmental dynamics of dilute perdeuteriopoly(ethylene oxide) (d4PEO) in equilibrium miscible mixtures with four low molecular weight glass-formers: indomethacin, sucrose benzoate, o-terphenyl, and toluene. Results are compared with literature data for dilute PEO in two polymer hosts: poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc). The segmental dynamics of PEO are found to strongly correlate with the dynamics of both high and low molecular weight hosts. For dilute PEO in mixtures with PMMA, PVAc, and sucrose benzoate, the Lodge–McLeish model with a ϕself (self-concentration) of 0.35 gives a good fit to the dynamics of dilute PEO, similar to previously reported dilute polyisoprene blends and dilute polystyrene blends. A smaller ϕself is obtained for dilute PEO in indomethacin, consistent with the presence of a hydrogen-bonding effect. For PEO in o-terphenyl and toluene, the implementation of the Lodge–McLeish model utilized here fails to give quantitative fits for the dynamics of the dilute PEO chains; this result is obtained because the full temperature-dependent host dynamics are not utilized in the fitting procedure.

Correlations between Ion Conductivity and Polymer Dynamics in Hyperbranched Poly(ethylene oxide) Electrolytes for Lithium-Ion Batteries

Poly(ethylene oxide)s with varying degrees of hyperbranching are effective at preventing the crystallization of PEO and lead to approximately a 100-fold increase in the Li-ion conductivity below 50 °C as compared with linear PEO. The Li-ion conductivities, which increase further upon permethylation of the hydroxyl termini, are found to correlate quantitatively with the fast segmental dynamics of PEO as measured by inelastic neutron scattering.

Understanding the Lithium Transport within a Rouse-Based Model for a PEO/LiTFSI Polymer Electrolyte

MD simulations of poly(ethylene oxide) (PEO) doped with lithium-bis(trifluoromethane)sulfonimide (LiTFSI) are analyzed with respect to the cation dynamics, the PEO dynamics as well as their coupling. Different cation transport mechanisms can be identified. These observations can be interpreted in terms of a recently proposed model of cation transport in polymer electrolytes. The model was capable of reproducing the lithium mean square displacement and self-diffusion coefficient. Because of the importance of interchain ion transfers for long-range ion transport, additional focus lies on the analysis of cations coordinated by two PEO chains, which is a common motif in this system.

Poly(ethylene oxide) Dynamics in Blends with Poly(vinyl acetate): Comparison of Segmental and Terminal Dynamics

Deuterium NMR at Larmor frequencies of 15.6 and 76.7 MHz was used to study the segmental dynamics of perdeuteriopoly(ethylene oxide) (d4PEO) in miscible blends with poly(vinyl acetate) (PVAc). Blends with PEO compositions of 2% and 50% were studied. The segmental dynamics of PEO are 9 orders of magnitude faster than the PVAc segmental dynamics for a 2% PEO blend near the blend Tg and could be described by the Lodge−McLeish model with a self-concentration of 0.3. The segmental dynamics of PEO in blends with PVAc show a weaker temperature dependence than the terminal dynamics of PEO in the same blends. We also compare the segmental and terminal dynamics of components in several other miscible polymer blends. For the fast component in a blend, it is commonly observed that terminal relaxation has a stronger temperature dependence than segmental relaxation. This effect correlates with the difference between the Tg values for the pure components and also with the ratio of the activation energies of the segmenta...

Role of Effective Composition on Dynamics of PEO−PMMA Blends

We use molecular simulation to compare component dynamics of a poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend with that of a diblock copolymer of the same overall composition. The blend and the copolymer have different intermolecular packing, which leads to a difference in compositions defined over local length scales. These directly impact dynamic behavior through the chain connectivity model for blend dynamics, which is based on a single controlling length scale for dynamics equal to the Kuhn length. By comparing the change in dynamics expected on the basis of different concentrations with the actual change observed in the simulations, we find that this idea is quantitatively accurate for the PMMA component. For PEO, the controlling length scale for dynamics varies with the size of the observation volume. In the concentration fluctuation model, 3,6,7 the local composition differs from the bulk value because of fluctuations related to thermodynamics. The magnitude of these fluctuations depends on proximity to the critical point and depends on component molecular weights, the use of deuterium labels, and the interaction parameter, � . The relevant dynamic length scale is the cooperative volume as described by Donth for the glass transition. 8,9 This varies but can be regarded as on the order of 10-30 nm. In the chain connectivity model, 10 the local composition differs from the bulk value because of covalent bonding along the chain backbone. In this case, the controlling volume for dynamics is the Kuhn length, lk, of each component, on the order of 10 A. This volume is sufficiently small that chain connectivity will significantly alter its composition compared to bulk values. In what follows we consider two systems in which the local composition varies over length scales of 5-25 A, while keeping other system variables (bulk composition, identities of the two components) constant. This is accomplished by comparing a blend of two homopolymers with a diblock copolymer in which the same two polymers form the two blocks, with lengths that result in the same overall composition. We use molecular simulation, with which the local composition is easily characterized as a function of length scale. Because of the small size of the simulated chains, concentration fluctuations related to thermodynamics are minimal, thus isolating the role of local composition arising from local packing and connectivity. The two systems present different intermo- lecular packing, resulting in different values of the local composition throughout the length scales mentioned above. These length scales are not relevant to concentration fluctuations but provide a useful test of the chain connectivity model. Specifically, it will address the question of the appropriate controlling length scale for mixture dynamics. In the chain connectivity model, the local composition of each component is defined via an effective concentration: 10

Fragmentation-Based QM/MM Simulations: Length Dependence of Chain Dynamics and Hydrogen Bonding of Polyethylene Oxide and Polyethylene in Aqueous Solutions

Molecular fragmentation quantum mechanics (QM) calculations have been combined with molecular mechanics (MM) to construct the fragmentation QM/MM method for simulations of dilute solutions of macromolecules. We adopt the electrostatics embedding QM/MM model, where the low-cost generalized energy-based fragmentation calculations are employed for the QM part. Conformation energy calculations, geometry optimizations, and Born-Oppenheimer molecular dynamics simulations of poly(ethylene oxide), PEO(n) (n = 6-20), and polyethylene, PE(n) ( n = 9-30), in aqueous solution have been performed within the framework of both fragmentation and conventional QM/MM methods. The intermolecular hydrogen bonding and chain configurations obtained from the fragmentation QM/MM simulations are consistent with the conventional QM/MM method. The length dependence of chain conformations and dynamics of PEO and PE oligomers in aqueous solutions is also investigated through the fragmentation QM/MM molecular dynamics simulations.

Dynamics of PEO in Blends with PMMA: Study of the Effects of Blend Composition via Quasi-Elastic Neutron Scattering

We address the dynamic behavior of poly(ethylene oxide) [PEO] in miscible blends with poly(methyl methacrylate) [PMMA] by using quasi-elastic neutron scattering [QENS] with isotopic labeling. The d...

Long-term aging effects on the rheology of neat laponite and laponite–PEO dispersions

We observe aging behavior of neat laponite systems over the course of 1,000 or more days. Under basic conditions, low laponite concentrations (1 wt%) slowly evolve from a viscoelastic liquid to a glass made of clusters acting as constituent elements interacting via long-range repulsion. Higher concentrations of laponite (3 wt%) quickly form a glass of individual particles. Intermediate concentrations of laponite form a glass that is a combination of clusters and individual particles. The aging rheological response and upturn of the loss modulus at low frequencies are well predicted by models of soft glassy systems (Fielding et al., J Rheol, 44(2):323–369, 2000; Sollich, Phys Rev E, 58(1):738–759, 1998). If low amounts of high-molecular-weight (Mn ≥ 163 kg/mol) poly(ethylene oxide) (PEO) are added, the aging behavior follows the dynamical response of the clay. Above a critical ratio, φ, of the free polymer chains in solution to the total laponite surface area, the PEO dynamics dominate at high frequencies. It appears that the dynamics of these complex laponite-PEO systems are governed by the parameter φ.

Dynamics of PEO–PPO–PEO triblock copolymer in aqueous solutions investigated byinternal friction

The dynamics of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethyleneoxide) (PEO–PPO–PEO) in aqueous solutions in the range of the polymer concentrationϕ = 10.0–45.0 wt% has been investigated by the tube inversion method and the internal friction technique.At ϕ≤31.0 wt%, two internal friction peaks are observed with the characteristics of the first-order phasetransition, corresponding to the opaque liquid-to-liquid transition and the phase separation.The opaque liquid-to-liquid transition is due to the sphere-to-rod transition in shape of themicelles, and the phase separation is caused by the destruction of core–shell structure. Atϕ≥32.0 wt%, besides the internal friction peak associated with phase separation, two other peaksare observed, which correspond to the solution-to-gel (liquid-to-crystal) transition andgel-to-solution (crystal-to-liquid) transition, respectively. The former is due to the micellecrystallization, whereas the latter is the result of spherical micelles fusing into wormlike orrodlike micelles at elevated temperatures.

Dynamic Confinement Effects in Polymer Blends. A Quasielastic Neutron Scattering Study of the Dynamics of Poly(ethylene oxide) in a Blend with Poly(vinyl acetate)

Quasielastic neutron scattering combined with deuteration labeling has allowed us to follow selectively the dynamics of the hydrogens of poly(ethylene oxide) (PEO, Tg ≈ 220 K) in a blend with poly(vinyl acetate) (PVAc, Tg = 315 K) (20% PEO/80% PVAc in weight, = 280 K). Temperatures between −10 K and + 120 K have been explored by backscattering techniques, accessing a dynamical window centered on the nanosecond range and with momentum transfers Q in the inter- and intrachain region. Two essentially different dynamical behaviors have been identified for PEO in the blend: (i) at high temperatures (≈ + 100 K) the dynamics is not qualitatively different from that of a glass-forming homopolymer (regarding spectral shape and dispersion of the time scales); (ii) close to , extremely broad distributions of relaxation times are found that do not depend on Q in the high-Q range, strongly suggesting localized dynamics. Apparently, the slowing down of the motions in the PVAc component toward leads to the confinement of PEO dynamics on small length scales. As soon as the dynamics of the more rigid polymer becomes fast enough to allow PEO long-range relaxations (≈ Tg + 80 K), the fast component reaches a situation of certain equilibrium, at least for length scales of the order of a nanometer. Our results perfectly agree with those reported for PEO in a blend with poly(methyl methacrylate) [Genix et al. Phys. Rev. E 2005, 72, 031808]. The confined processes in both “rigid environments” show nearly identical features. In addition, neutron diffraction experiments with polarization analysis indicate that, while blending hardly affects the short-range order of PVAc chains, it leads to larger and more distributed characteristic distances involving PEO segments.

Effect of cation exchange capacity on the structure and dynamics of poly(ethylene oxide) in Li+ montmorillonite nanocomposites

AbstractMolecular dynamics computer simulations are used to study the structure and dynamics of 1‐nm wide films of poly(ethylene oxide) (PEO) confined between mica‐type layered silicates of different cation exchange capacities (CEC). The simulation setup mimics experimental systems formed by intercalation of PEO in montmorillonite alumino‐silicates with varied inherent charges. It is shown that the presence and population of lithium has a significant influence on the behavior of the system, in addition to the confinement‐induced effects caused by the extreme spatial restriction. The structural features of the confined PEO are strongly altered with the number of Li+, which determines the polymer/inorganic interactions. The combination of the nanoconfinement and the presence of lithium preclude regular ordered arrangements of PEO, similar to those observed in the bulk unconfined polymer. The segmental dynamics of PEO in confinement are also greatly influenced by the presence of lithium, because of the strong interaction between Li+ and the oxygen of the PEO backbone. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3460–3477, 2005