Interchain coupled chain dynamics of poly(ethylene oxide) in blends with poly(methyl methacrylate): coupling model analysis

Quasielastic neutron scattering and molecular dynamics simulation data from poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends found that for short times the self-dynamics of PEO chain follows the Rouse model, but at longer times past t(c) = 1-2 ns it becomes slower and departs from the Rouse model in dependences on time, momentum transfer, and temperature. To explain the anomalies, others had proposed the random Rouse model (RRM) in which each monomer has different mobility taken from a broad log-normal distribution. Despite the success of the RRM, Diddens et al. [Eur. Phys. Lett. 95, 56003 (2011)] extracted the distribution of friction coefficients from the MD simulations of a PEO/PMMA blend and found that the distribution is much narrower than expected from the RRM. We propose a simpler alternative explanation of the data by utilizing alone the observed crossover of PEO chain dynamics at t(c). The present problem is just a special case of a general property of relaxation in interacting systems, which is the crossover from independent relaxation to coupled many-body relaxation at some t(c) determined by the interaction potential and intermolecular coupling/constraints. The generality is brought out vividly by pointing out that the crossover also had been observed by neutron scattering from entangled chains relaxation in monodisperse homopolymers, and from the segmental α-relaxation of PEO in blends with PMMA. The properties of all the relaxation processes in connection with the crossover are similar, despite the length scales of the relaxation in these systems are widely different.     

Investigating the effect of nanolayered silicates on blend segmental dynamics and minor component relaxation behavior in poly(ethylene oxide)/poly(methyl methacrylate) miscible blends

Polymer–silicate nanocomposites based on poly (ethylene oxide), PEO, poly(methyl methacrylate), PMMA, and sodium montmorillonite clay were fabricated and characterized to investigate the effect of nanolayered silicates on segmental dynamics of PEO/PMMA blends. X‐ray results indicate the formation of an exfoliated morphology in the nanocomposites. At low silicate contents, an enhancement in segmental dynamics of blend nanocomposites and also PEO, minor component in blend, is observed at temperature region below blend glass transition. This result can be attributed to the improvement of the confinement effect of rigid PMMA matrix on the PEO chains by introducing a low amount of layered silicates. On the other hand, at high silicate contents, an enhancement in segmental dynamics of blend nanocomposites and PEO is observed at temperature region above blend glass transition. This behavior could be interpreted based on the reduction of monomeric friction between two polymer components, which can facilitate segmental motions of blend components in nanocomposite systems. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Deuterium solid echo line shape study of poly(ethylene oxide) dynamics in a blend with poly(methyl methacrylate)

Deuterium solid echo line shapes were measured on deuterated poly(ethylene oxide) (d₄PEO) in a blend with protonated poly(methyl methacrylate) to characterize chain dynamics of this component in the blend. Line shapes were observed as a function of temperature from 183 to 243 K and echo delay times from 10 to 100 μs on a blend containing 20 wt % d₄PEO. The line shapes and the associated relative intensities were quantitatively interpreted in terms of segmental motion and libration. The results of the interpretation are compared to an earlier study of deuterium spin‐lattice relaxation times over the temperature range of 313 to 413 K. A combined interpretation of both sets of data is developed based on bimodal distribution of correlation times that are separated by about 2 orders of magnitude in time. The faster mode is 30% of the correlation function with a stretched exponent near one while the slower mode is characterized by an exponent of 0.5. The source of the bimodal character is not revealed by the line shape and relaxation data but is consistent with the presence of two glass transition temperatures in this miscible blend and anomalous translational diffusion of diethyl ether through the blend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2433–2444, 2005     

Anomalous penetrant diffusion as a probe of the local structure in a blend of poly(ethylene oxide) and poly(methyl methacrylate)

Pulse field gradient (PFG) NMR measurements have been made to study the diffusion of diethyl ether in blends of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA). The blends have 10–30 wt % PEO, a composition range within which these materials are amorphous glasses. The diffusion of diethyl ether through the blends is quite rapid, with diffusion constants in the range of 10^?7 to 10^?8 cm²/s. In PFG NMR experiments, the apparent diffusion constant depends on the timescale over which diffusion is observed. The values decrease to a plateau as the time increases, this being the signature of tortuous diffusion. Tortuous diffusion is usually observed in heterogeneous systems in which there are regions that support fast diffusion and regions that support slow diffusion or act as barriers. In these blends, PEO is known to undergo rapid segmental motion typical of a rubbery state well below the glass transition, whereas the segmental motion of PMMA is slower by many orders of magnitude. Mobile PEO provides a pathway for the diffusion of structurally similar diethyl ether, whereas solid‐like PMMA acts as a barrier. The size of the domains can be estimated either from a lattice model or from equations for tortuous diffusion. Micrometer sizes are indicated that are unexpectedly large, given the size of the polymer chains and the size of the concentration fluctuations, both of which are thought to be in the tens of nanometers. The lattice model and the equations for tortuous diffusion assume a random dispersion of impenetrable or less penetrable objects. This may not be the appropriate morphology for the diffusion pathway. Recently, large sizes have been indicated by PFG NMR experiments, in which a penetrant is thought to diffuse in a curvilinear fashion. In these blends, the pathway for diethyl ether is along the PEO backbone. A plot of the logarithm of the mean‐square displacement versus the logarithm of time has a slope of about 0.6, close to the value of 0.5 for pure curvilinear diffusion. Exponents with values in this range can also be associated with diffusion in a fractal space, which, in this situation, still consists of mobile PEO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1053–1067, 2004     

Polymer chain diffusion in polymer blends: A theoretical interpretation based on a memory function formalism

The diffusion of polymer chains in miscible polymer blends with large dynamic asymmetry—those where the two blend components display very different segmental mobility—is not well understood yet. In the extreme case of the blend system of poly(ethylene oxide) (PEO) and poly(methyl methacrylate)(PMMA), the diffusion coefficient of PEO chains in the blend can change by more than five orders of magnitude while the segmental time scale hardly changes with respect to that of pure PEO. This behavior is not observed in blend systems with small or moderate dynamic asymmetry as, for instance, polyisoprene/poly(vinyl ethylene) blends. These two very different behaviors can be understood and quantitatively explained in a unified way in the framework of a memory function formalism, which takes into account the effect of the collective dynamics on the chain dynamics of a tagged chain. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1239–1245     

Effect of chain length on fragility and thermodynamic scaling of the local segmental dynamics in poly(methylmethacrylate)

Local segmental relaxation properties of poly(methylmethacrylate) (PMMA) of varying molecular weight are measured by dielectric spectroscopy and analyzed in combination with the equation of state obtained from PVT measurements. Significant variations of glass transition temperature and fragility with molecular weight are observed. In accord with the general properties of glass-forming materials, single molecular weight dependent scaling exponent gamma is sufficient to define the mean segmental relaxation time taualpha and its distribution. This exponent can be connected to the Gruneisen parameter and related thermodynamic quantities, thus demonstrating the interrelationship between dynamics and thermodynamics in PMMA. Changes in the relaxation properties ("dynamic crossover") are observed as a function of both temperature and pressure, with taualpha serving as the control parameter for the crossover. At longer taualpha another change in the dynamics is apparent, associated with a decoupling of the local segmental process from ionic conductivity.     

Thermal oxidation of blends of poly(ethylene oxide) and poly(methyl methacrylate)

Thermal oxidation of poly(ethylene oxide) (PEO) and its blends with poly(methyl methacrylate) (PMMA) were studied using oxygen uptake measurements. The rates of oxidation and maximum oxygen uptake contents were reduced as the content of PMMA was increased in the blends. The results were indicative of a stabilizing effect by PMMA on the oxidation of PEO. The oxidation reaction at 140°C was stopped at various stages and PMMA was separated from PEO and its molecular weights were measured by gel permeation chromatography (GPC). The decrease in the number-average molecular weight of PMMA was larger as the content of PEO increased in the blends. The visual appearance of the films suggested that phase separation did not occur after thermal oxidation. The activation energy for the rates of oxidation in the blends was slightly increased compared to pure PEO. © 1992 John Wiley & Sons, Inc.     

Rheology of poly(methyl methacrylate) Langmuir monolayers: percolation transition to a soft glasslike system

An experimental study of the equilibrium properties and of the surface rheology of Langmuir monolayers of poly(methyl methacrylate) (PMMA) at the air/water interface has been carried out as a function of polymer concentration (Γ) and molecular weight (M(w)). Dilational and shear complex elasticity moduli covering a frequency range from 10(-3) to 0.2 Hz have been discussed. It was found that the air∕water interface behaves as a poor solvent for PMMA monolayers, thus suggesting that the polymer coils take collapsed soft-disks (pancakes) shape at the interface. The equilibrium and dynamic results suggest a fluid-to-soft-glass transition as the polymer concentration increases above a critical packing fraction at constant temperature. This two-dimensional transition is in agreement with results previously discussed for the dilational rheology of poly(4-hydroxystyrene) [F. Monroy, F. Ortega, R. G. Rubio, H. Ritacco, and D. Langevin, J. Chem. Phys. 95, 056103 (2005)]. Furthermore, the Γ-dependence of the relaxation dynamics of the monolayers suggests that the gel state may be considered as a fragile soft glass.     

Crystallization of poly(ethylene oxide) in binary polymer blends: Influence of tacticity of poly(methyl methacrylate)

Kinetics of the crystallization of poly(ethylene oxide) (PEO) from the PEO blends with syndiotactic, atactic, or isotactic poly(methyl methacrylate) (s-, a-, and i-PMMA) was investigated. The isothermal spherulitic growth rates were measured with an optical microscope. The influence of the composition of the blends, the tacticity of PMMA, and temperature on the growth rates were studied. Linear growth rates were observed regardless of the tacticity. The growth rates of spherulites are markedly reduced by a-PMMA and s-PMMA. However the growth rates of PEO are hardly influenced by i-PMMA. Such observations are interpreted by assuming that PEO forms miscible blends with a- and s-PMMA in the molten states, whereas it does not from with i-PMMA.     

Enhanced ionic conductivity in PEO/PMMA glassy miscible blends: Role of nano‐confinement of minority component chains

AC impedance spectroscopy was used to investigate the ionic conductivity of solution cast poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends doped with lithium perchlorate. At low PEO contents (below overlap weight fraction w^*), ionic conductivities are almost low. This could be due to nearly distant PEO chains in blend, which means ion transportation cannot be performed adequately. However, at weight fractions well above w^*, a significant increase in ionic conductivity was observed. This enhanced ionic conductivity mimics the PEO segmental relaxation in rigid PMMA matrix, which can be attributed to the accelerated motions of confined PEO chains in PMMA matrix. At PEO content higher than 20 wt % the conductivity measured at room temperature drops due to crystallization of PEO. However by increasing temperature to temperatures well above the melting point of PEO, a sudden increase of conductivity was observed which was attributed to phase transition from crystalline to amorphous state. The results indicate that some PEO/PMMA blends with well enough PEO content, which are structurally solid, can be considered as an interesting candidate for usage as solid‐state electrolytes in Lithium batteries. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2065–2071, 2010     

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (M _N)=6.0×10³, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35?°C. ESR spectra were measured at various temperatures after the samples were completely dried. The ESR spectra are composed of two spectra arising from spin-labels attached to “train” and “tail” segments, which are strongly and weakly interacted with the silica surface, respectively. The fractional amount of the “tail” segments increases extremely with the grafting ratio of PMMA. Molecular mobility of the PEO chains estimated from the temperature dependence of the ESR spectra also decreases significantly with the grafting ratio of PMMA. Structure and molecular motion of the PMMA chains tethered on the silica were also studied using the spin-labelled PMMA. Consequently, parts of the PEO segments penetrate into the PMMA chains and is adsorbed on the silica surface (“train” segments), whereas parts of the PMMA segments protrude from the surface. The other PEO segments are entangled with the tethered PMMA chains (“tail” segments).     

Free volume holes diffusion to describe physical aging in poly(mehtyl methacrylate)/silica nanocomposites

The spontaneous thermodynamically driven densification, the so-called physical aging, of glassy poly(mehtyl methacrylate) (PMMA) and its nanocomposites with silica has been described by means of the free volume holes diffusion model. This mechanism is able to account for the partial decoupling between physical aging and segmental dynamics of PMMA in nancomposites. The former has been found to be accelerated in PMMA/silica nanocomposites in comparison to "bulk" PMMA, whereas no difference between the segmental dynamics of bulk PMMA and that of the same polymer in nanocomposites has been observed. Thus, the rate of physical aging also depends on the amount of interface polymer/nanoparticles, where free volume holes disappear after diffusing through the polymer matrix. The free volume holes diffusion model is able to nicely capture the phenomenology of the physical aging process with a structure dependent diffusion coefficient.     

Neutron scattering investigation of a diluted blend of poly(ethylene oxide) in polyethersulfone

By using quasielastic neutron scattering (QENS) with isotopic labeling we have investigated the component dynamics in a miscible blend of polyethersulfone (PES) and poly(ethylene oxide) (PEO) with 75% content in weight of PES. Due to the large difference in the glass-transition temperatures, T(g)'s, of the two polymers (T(g) (PEO) approximately equal to 220 K, T(g) (PES) approximately equal to 382 K) the dynamic asymmetry in the system dramatically increases when approaching the average T(g) of the blend, . For the fast (PEO) component, this leads to a behavior which hints a crossover from typical glass-forming liquidlike dynamics at high temperatures to confined dynamics close to induced by the freezing of the segmental motions of the slow PES. The features of the confined PEO motion observed by QENS are similar to those of the secondary gamma-relaxation detected for pure (semicrystalline) PEO. A neutron diffraction study of the short-range order of the homopolymers and the blend suggests that this coincidence could be due to similarities in the intermolecular packing of PEO and PES polymers.     

Effects of the volume and temperature on the global and segmental dynamics in poly(propylene glycol) and 1,4‐polyisoprene

Published dielectric relaxation measurements for poly(propylene glycol) and 1,4‐polyisoprene are analyzed to determine the relative effects that thermal energy and volume have on the temperature dependence of the normal‐mode relaxation times, and these are compared with their effects on the temperature dependence of the local segmental relaxation times. For both polymers at temperatures well above the glass‐transition temperature, both relaxation modes are governed more by the thermal energy than by the volume, although the latter's contribution is not negligible. Such a result is consistent with an assumption underlying models for polymer viscoelasticity, such as the Rouse and tube models, that the friction coefficient governing motions over large length scales can be identified with the local segmental friction coefficient. Moreover, the relaxation data for both the segmental and normal modes superimpose when expressed as a function of the product of the temperature and volume, the latter being raised to a power. This scaling form arises from an inverse power law for the repulsive part of the intermolecular potential. The value of the exponent on the volume is the same for the normal and segmental motions and for both polymers indicates a relatively soft potential. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4313–4319, 2004     

Uniaxial drawing of poly(ethyleneoxide)/poly(methyl methacrylate) blends by solid-state extrusion

Ultradrawn ribbons of solution-cast blends of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) have been prepared by a solid-state coextrusion in a capillary rheometer. An increase of noncrystallizable PMMA in the blends drastically decreased the drawability from a draw ratio of 36 for pure PEO to 5 for a mixture of PEO/PMMA 40/60% by weight. A low crystallinity and depression of melting temperature for PEO were observed with increasing draw. The Flory-Huggins theory for melting temperature depression has been used to derive the binary interaction parameter for these blends.     

Dielectric relaxation and aging effect in interpenetrating network polymers of poly(urethane)-poly(methyl methacrylate)

The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol-1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 10⁵ Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, α_pu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature-frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)-PMMA causes its γ process to become indiscernible and the α_pu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided.     

Ion conduction and polymer dynamics of poly(2-vinylpyridine)-lithium perchlorate mixtures

Ion conduction and polymer dynamics of homogeneous mixtures of poly(2-vinylpyridine) (P2VPy) with 0.1 to 10 mol % lithium perchlorate (LiClO(4)) were investigated using broadband dielectric spectroscopy. Interpretation of the relaxation behavior was assisted by findings from differential scanning calorimetry, Fourier transform infrared spectroscopy, dynamic mechanical analysis, and wide-angle and small-angle X-ray scattering experiments. Five dielectric relaxations were observed: a local beta-process in the glassy state, a segmental relaxation, a slow segmental process, an ion-mode relaxation, and electrode polarization. The local P2VPy beta-relaxation was strongly suppressed with increasing LiClO(4) content arising from the formation of transient crosslinks, which lead to a subsequent decrease in the number of free pyridine groups and/or a reduction in the local free volume in the presence of LiClO(4). Ion conduction at low LiClO(4) concentrations (<10 mol %) is governed by the diffusion of anions through the matrix, which is strongly coupled with the segmental relaxation. At relatively high LiClO(4) concentration (10 mol %), partial decoupling between ion motion and the segmental relaxation was observed, leading to increased conductivity.     

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SC CO₂) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO₂ treatment. The enhancement of PEO crystallization with SC CO₂ treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO₂ treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO₂ treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004     

Using neutron reflectivity to determine the dynamic properties of a copolymer in a homopolymer matrix

A protocol for using neutron reflectivity to monitor the dynamic properties of a copolymer in a homopolymer matrix is described. This technique may be used to monitor a broad range of systems, as long as the copolymer and homopolymer form a miscible blend at low copolymer concentrations. Moreover, with knowledge of the Flory–Huggins interaction parameter between the copolymer and homopolymer, the molecular dynamic parameters of the copolymer, such as the tracer diffusion coefficient, segmental friction factor, and longest relaxation time, can be quantitatively determined. This technique is demonstrated by the determination of these parameters for a series of styrene/methyl methacrylate alternating copolymers dispersed in a matrix of deuterated poly(methyl methacrylate). Interestingly, the segmental friction factor of these alternating copolymers is significantly different from that of similar diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3235–3247, 2004     

A generalized method to calculate diffusion rates in polydisperse systems. Further results on Rouse dynamics in the concentrated regime

Experiments designed to thoroughly test a recently proposedgeneralized method to calculate diffusion rates in polydisperse systems have been carried out. Polydisperse polystyrene (PS) samples were allowed to diffuse in a poly(phenylene oxide) (PPO) matrix. Designed blends were made from anionically polymerized PS with molecular weights which cover most of the ranges where Rouse dynamics control the diffusion processes. The diffusion temperatures range from (T_g – 1 K) to (T_g + 105 K), causing the monomeric friction factor values for PS to change by up to seven orders of magnitude along the diffusion coordinate. Calculations performed with the above mentioned method agree with Raman and DMA experimental data.