Showing papers on "Glass transition published in 2009"
TL;DR: This work presents a model offering an improved description of the viscosity–temperature relationship for both inorganic and organic liquids using the same number of parameters as VFT and AM, and casts doubt on the existence of a Kauzmann entropy catastrophe and associated ideal glass transition.
Abstract: The low-temperature dynamics of ultraviscous liquids hold the key to understanding the nature of glass transition and relaxation phenomena, including the potential existence of an ideal thermodynamic glass transition. Unfortunately, existing viscosity models, such as the Vogel–Fulcher–Tammann (VFT) and Avramov–Milchev (AM) equations, exhibit systematic error when extrapolating to low temperatures. We present a model offering an improved description of the viscosity–temperature relationship for both inorganic and organic liquids using the same number of parameters as VFT and AM. The model has a clear physical foundation based on the temperature dependence of configurational entropy, and it offers an accurate prediction of low-temperature isokoms without any singularity at finite temperature. Our results cast doubt on the existence of a Kauzmann entropy catastrophe and associated ideal glass transition.
791 citations
TL;DR: Direct nanopatterning of metallic glasses by hot embossing is demonstrated, generating feature sizes as small as 13 nm, and it is shown that another amorphous sample of the same alloy can be formed on the crystallized mould.
Abstract: Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds. Silicon-based moulds are brittle and have limited longevity. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations. Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this 'spawning' process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials.
659 citations
TL;DR: In this article, the main phenomenological traits of supercooled liquids are discussed and a few theoretical ideas on the subject are discussed in a very partial way, and the correlation length associated to the sharp increase of the relaxation time is discussed.
Abstract: When we lower the temperature of a liquid, at some point we meet a first order phase transition to the crystal. Yet, under certain conditions it is possible to keep the system in its metastable phase and to avoid crystallization. In this way the liquid enters in the supercooled phase. Supercooled liquids have a very rich phenomenology, which is still far from being completely understood. To begin with, there is the problem of how to prevent crystallization and how deeply the liquid can be supercooled before a metastability limit is hit. But by far the most interesting feature of supercooled liquids is the dynamic glass transition: when the temperature is decreased below a certain point, the relaxation time increases so much that a dramatic dynamical arrest intervenes and we are unable to equilibrate the system within reasonable experimental times. The glass transition is a phenomenon whose physical origin has stirred an enormous interest in the last hundred years. Why does it occur? Is it just a conventional reference point, or does it have a more profound physical meaning? Is it a purely dynamical event, or the manifestation of a true thermodynamic transition? What is the correlation length associated to the sharp increase of the relaxation time? Can we define a new kind of amorphous order? A shared theory of supercooled liquids and the glass transition does not yet exist and these questions are still largely open. Here, I will illustrate in the most elementary fashion the main phenomenological traits of supercooled liquids and discuss in a very partial way a few theoretical ideas on the subject.
563 citations
TL;DR: It is shown that deformable colloidal particles, when studied through their concentration dependence at fixed temperature, do exhibit the same variation in fragility as that observed in the T dependence of molecular liquids at fixed volume.
Abstract: Glass formation in colloidal suspensions has many of the hallmarks of glass formation in molecular materials. For hard-sphere colloids, which interact only as a result of excluded volume, phase behaviour is controlled by volume fraction, phi; an increase in phi drives the system towards its glassy state, analogously to a decrease in temperature, T, in molecular systems. When phi increases above phi* approximately 0.53, the viscosity starts to increase significantly, and the system eventually moves out of equilibrium at the glass transition, phi(g) approximately 0.58, where particle crowding greatly restricts structural relaxation. The large particle size makes it possible to study both structure and dynamics with light scattering and imaging; colloidal suspensions have therefore provided considerable insight into the glass transition. However, hard-sphere colloidal suspensions do not exhibit the same diversity of behaviour as molecular glasses. This is highlighted by the wide variation in behaviour observed for the viscosity or structural relaxation time, tau(alpha), when the glassy state is approached in supercooled molecular liquids. This variation is characterized by the unifying concept of fragility, which has spurred the search for a 'universal' description of dynamic arrest in glass-forming liquids. For 'fragile' liquids, tau(alpha) is highly sensitive to changes in T, whereas non-fragile, or 'strong', liquids show a much lower T sensitivity. In contrast, hard-sphere colloidal suspensions are restricted to fragile behaviour, as determined by their phi dependence, ultimately limiting their utility in the study of the glass transition. Here we show that deformable colloidal particles, when studied through their concentration dependence at fixed temperature, do exhibit the same variation in fragility as that observed in the T dependence of molecular liquids at fixed volume. Their fragility is dictated by elastic properties on the scale of individual colloidal particles. Furthermore, we find an equivalent effect in molecular systems, where elasticity directly reflects fragility. Colloidal suspensions may thus provide new insight into glass formation in molecular systems.
495 citations
TL;DR: In this paper, the shape memory transition temperature of an amorphous SMP polymers is tuned by changing the crosslink density and the aliphatic epoxy chain length.
482 citations
TL;DR: Numerical evidence is presented for the existence of a novel first-order dynamical phase transition in atomistic models of structural glass formers, offering the possibility of a unified picture of glassy phenomena.
Abstract: The glass transition is the freezing of a liquid into a solid state without evident structural order. Although glassy materials are well characterized experimentally, the existence of a phase transition into the glass state remains controversial. Here, we present numerical evidence for the existence of a novel first-order dynamical phase transition in atomistic models of structural glass formers. In contrast to equilibrium phase transitions, which occur in configuration space, this transition occurs in trajectory space, and it is controlled by variables that drive the system out of equilibrium. Coexistence is established between an ergodic phase with finite relaxation time and a nonergodic phase of immobile molecular configurations. Thus, we connect the glass transition to a true phase transition, offering the possibility of a unified picture of glassy phenomena.
384 citations
TL;DR: In this article, isolated graphene sheets were achieved by graphite intercalation and charge-induced exfoliation, and the resultant graphene oxide sheets were incorporated into polymer composites and thermal expansion was investigated by a thermo-mechanical analyzer.
Abstract: Isolated graphene sheets were achieved by graphite intercalation and charge-induced exfoliation. The resultant graphene oxide sheets were incorporated into polymer composites and thermal expansion was investigated by a thermo-mechanical analyzer. The test results indicated that inclusion of graphene into composites resulted in low coefficients of thermal expansion (CTEs), and increasing graphene fraction reduced CTEs more significantly. The 5 wt % graphene oxide-based composite shows 31.7% reduction below the glass transition temperature. Preliminary measurement of thermal conductivity also indicated that graphene composites significantly improved the thermal conductivity of polymer matrix. Thermal conductivity of 5% graphene composites showed about 4-fold increment in comparison to the polymer matrix. This finding will provide a solid foundation for graphene-enabled thermal management in microelectronics.
361 citations
TL;DR: The observed glass transition temperature (Tg) defines the operating window for the thermal annealing and explains the long-term instability of both the morphology and the photovoltaic performance of the P3HT/PCBM solar cells.
Abstract: In this work, the phase diagram of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends is measured by means of standard and modulated temperature differential scanning calorimetry. Blends were made by solvent-casting from chlorobenzene, as blends cast from toluene or 1,2-dichlorobenzene prove to retain effects of phase segregation during casting, hindering the determination of the phase diagram. The film morphology of P3HT/PCBM blends cast from chlorobenzene results from a dual crystallization behavior, in which the crystallization of each component is hindered by the other component. A single glass transition is observed for all compositions. The glass transition temperature (Tg) increases with increasing concentration of PCBM: from 12.1 degrees C for pure P3HT to 131.2 degrees C for pure PCBM. The observed Tg defines the operating window for the thermal annealing and explains the long-term instability of both the morphology and the photovoltaic performance of the P3HT/PCBM solar cells.
357 citations
TL;DR: This work addresses several unsolved problems regarding calorimetry of polymers, for example determination of baseline heat capacity, which is related to the problem of crystallinity determination by DSC, or the occurrence of multiple melting peaks.
Abstract: Differential scanning calorimetry (DSC) is an effective analytical tool to characterize the physical properties of a polymer. DSC enables determination of melting, crystallization, and mesomorphic transition temperatures, and the corresponding enthalpy and entropy changes, and characterization of glass transition and other effects that show either changes in heat capacity or a latent heat. Calorimetry takes a special place among other methods. In addition to its simplicity and universality, the energy characteristics (heat capacity CP and its integral over temperature T—enthalpy H), measured via calorimetry, have a clear physical meaning even though sometimes interpretation may be difficult. With introduction of differential scanning calorimeters (DSC) in the early 1960s calorimetry became a standard tool in polymer science. The advantage of DSC compared with other calorimetric techniques lies in the broad dynamic range regarding heating and cooling rates, including isothermal and temperature-modulated operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of DSCs. Rates as low as 1 μK s−1 are possible and at the other extreme heating and cooling at 1 MK s−1 and higher is possible. The broad dynamic range is especially of interest for semicrystalline polymers because they are commonly far from equilibrium and phase transitions are strongly time (rate) dependent. Nevertheless, there are still several unsolved problems regarding calorimetry of polymers. I try to address a few of these, for example determination of baseline heat capacity, which is related to the problem of crystallinity determination by DSC, or the occurrence of multiple melting peaks. Possible solutions by using advanced calorimetric techniques, for example fast scanning and high frequency AC (temperature-modulated) calorimetry are discussed.
303 citations
TL;DR: In this paper, the authors used dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres, and found that the system remains ergodic above c and enters a new dynamical regime where the amplitude of dynamic heterogeneity grows slower than a power law.
Abstract: We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, � � , including equilibrium measurements above ’c, the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above ’c and enters a new dynamical regime where � � increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with � � , as found in molecular glass formers close to the glass transition.
292 citations
TL;DR: An analytical expression is derived for the scaling of glass transition temperature and fragility in the binary Ge(x)Se(1-x) system with temperature-dependent constraints that freeze in as the system is cooled from high temperature.
Abstract: We present a topological model for the composition dependence of glass transition temperature and fragility. Whereas previous topological models are derived for zero temperature conditions, our approach incorporates the concept of temperature-dependent constraints that freeze in as the system is cooled from high temperature. Combining this notion of temperature-dependent constraints with the Adam-Gibbs model of viscosity, we derive an analytical expression for the scaling of glass transition temperature and fragility in the binary Ge(x)Se(1-x) system. In the range of 0
TL;DR: In this paper, the potential of lignin as a bio-resource is discussed, focusing on its characteristic structure and properties, such as its ability to be used as starting materials for synthetic polymers such as polyesters, polyethers and polystyrene derivatives.
Abstract: Polymeric features of lignin and its potential as a bio-resource are reviewed, focusing on its characteristic structure and properties. Lignin is a random copolymer consisting of phenylpropane units having characteristic side chains. Lignin slightly crosslinks and takes an amorphous structure in the solid state. The molecular motion is observed as glass transition by thermal, viscoelastic and spectroscopic measurements. The hydroxyl group of lignin plays a crucial role in interaction with water. By chemical and thermal decomposition, a wide range of chemicals can be obtained from lignin that can be used as starting materials for synthetic polymers, such as polyesters, polyethers, and polystyrene derivatives. At the same time, a variety of polymers can be derived from lignin by simple chemical modification. The hydroxyl group acts as a reaction site for the above chemical reaction.
TL;DR: It is shown that PNCs, prepared from athermal mixtures of polymer-chain-grafted gold nanoparticles and unentangled polymer chains, may exhibit increases or decreases in their relaxation dynamics, and viscosity, by over an order of magnitude through control of nanoparticle concentration, nanoparticle size, grafting density and grafting chain degree of polymerization.
Abstract: Tailoring the properties of polymer nanocomposites—polymers incorporating nanoparticles—is essential to develop biomedical, or even electronic, applications. It is now shown that accurate control of the nanoparticle concentration in nanocomposites prepared from athermal mixtures considerably varies the physical properties with respect to the host polymer.
TL;DR: In this paper, the effects of four dietary fiber sources (oat, wheat, apple and inulin) on the rheological and thermal properties of model sucrose-polysaccharides solutions and ice cream mixes were investigated.
TL;DR: A new topological modeling approach is developed that enables accurate prediction of the scaling of both glass transition temperature and fragility with composition and reveals a natural explanation for the presence of the constant T(g) regime observed in alkali borate systems.
Abstract: Glass transition temperature and fragility are two important properties derived from the temperature dependence of the shear viscosity of glass-forming melts. While direct calculation of these properties from atomistic simulations is currently infeasible, we have developed a new topological modeling approach that enables accurate prediction of the scaling of both glass transition temperature and fragility with composition. A key feature of our approach is the incorporation of temperature-dependent constraints that become rigid as a liquid is cooled. Using this approach, we derive analytical expressions for the composition (x) dependence of glass transition temperature, Tg(x), and fragility, m(x), in binary alkali borate systems. Results for sodium borate and lithium borate systems are in agreement with published values of Tg(x) and m(x). Our modeling approach reveals a natural explanation for the presence of the constant Tg regime observed in alkali borate systems.
TL;DR: In this paper, hollow glass microsphere (HGM)-filled epoxy composites, with filler content ranging from 0 to 51.3vol%, were prepared in order to modify the dielectric properties of the epoxy.
TL;DR: In this article, the effects of the coupling agent on composite properties was highly beneficial leading to increased moduli and heat deflection temperatures as well as reduced water swelling in a headliner.
TL;DR: In this article, a new class of aggregation-induced emission (AIE) compounds with strong blue-light-emitting properties and a high thermal stability, derived from triphenylethylene carbazole, has been synthesized.
Abstract: A new class of aggregation-induced emission (AIE) compounds with strong blue-light-emitting properties and a high thermal stability, derived from triphenylethylene carbazole, has been synthesized. Their glass transition temperatures range from 126–151 °C and the maximum fluorescence emission wavelengths are 451–466 nm.
TL;DR: It was concluded that, when an amorphous molecular level solid dispersion containing a hydrophobic drug and hydrophilic polymer is subjected to moisture, drug crystallization can occur via one of two routes: crystallization from the plasticized one-phaseSolid dispersion, or crystallized from a plasticized drug-rich amorphously phase in a two-phasesolid dispersion.
Abstract: The objective of this study was to investigate the phase behavior of amorphous solid dispersions composed of a hydrophobic drug and a hydrophilic polymer following exposure to elevated relative humidity. Infrared (IR) spectroscopy, differential scanning calorimetry (DSC) and moisture sorption analysis were performed on five model systems (nifedipine-poly(vinylpyrrolidone) (PVP), indomethacin-PVP, ketoprofen-PVP, droperidol-PVP, and pimozide-PVP) immediately after production of the amorphous solid dispersions and following storage at room temperature and elevated relative humidity. Complete miscibility between the drug and the polymer immediately after solid dispersion formation was confirmed by the presence of specific drug-polymer interactions and a single glass transition (T(g)) event. Following storage at elevated relative humidity (75-94% RH), nifedipine-PVP, droperidol-PVP, and pimozide-PVP dispersions formed drug-rich and polymer-rich amorphous phases prior to crystallization of the drug, while indomethacin-PVP and ketoprofen-PVP dispersions did not. Drug crystallization in systems exhibiting amorphous-amorphous phase separation initiated earlier ( or=46 days at 94% RH). Evidence of moisture-induced amorphous-amorphous phase separation was observed following storage at as low as 54% RH for the pimozide-PVP system. It was concluded that, when an amorphous molecular level solid dispersion containing a hydrophobic drug and hydrophilic polymer is subjected to moisture, drug crystallization can occur via one of two routes: crystallization from the plasticized one-phase solid dispersion, or crystallization from a plasticized drug-rich amorphous phase in a two-phase solid dispersion. In the former case, the polymer is still present in the same phase as the drug, and can inhibit crystallization to a greater extent than the latter scenario, where the polymer concentration in the drug phase is reduced as a result of the amorphous-amorphous phase separation. The strength of drug-polymer interactions appears to be important in influencing the phase behavior.
TL;DR: In this article, a correlation was made between crystallization, various morphological parameters and the barrier properties of poly(lactic acid) and showed that the presence of a rigid amorphous fraction with lower density can have strong impact on PLA gas permeability, in particular on the gas solubility coefficient.
Abstract: Poly(lactic acid) is at present the most promising and commercially available bio-based and biocompostable (bio)plastic. The properties of PLA, however, are rather poor, notably its low glass transition temperature Tg of ∼55 °C, its intrinsic low crystallization rate and the limited barrier properties with respect to water, oxygen and carbon dioxide in comparison with to oil-based counterparts, notably polyesters (PET). In this manuscript we address the question of what could ultimately be achieved in terms of barrier properties when PLA is crystallized fully. In fact, this question is rather academic in view of the long crystallization/annealing times needed to obtain maximum crystallinity but serves the purpose of better understanding current limits and notably a better understanding of the role of crystallinity on the barrier properties. A correlation is made between crystallization, various morphological parameters and the barrier properties of PLA. Crystallization of PLA causes a decrease of the oxygen permeability, but not in linear proportion with the decrease in amorphous volume. We explain this in terms of influence of the space filling and the inner crystalline structure on gas transport properties. Furthermore we suggest that the presence of a rigid amorphous fraction with lower density can have strong impact on PLA gas permeability, in particular on the gas solubility coefficient of PLA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2247–2258, 2009
TL;DR: In this article, the compatibility, phase structure, and component interaction of poly(lactic acid) (PLA) and glycidyl methacrylate grafted poly(ethylene octane) (GMA-g-POE denoted as mPOE) blend by Fourier transform infrared (FTIR) spectra, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD), respectively.
TL;DR: In this paper, the authors performed magnetic susceptibility measurements on RuSr2Eu15Ce05Cu2O10−δ (Ru1222) material and found that the magnetization versus applied field loops do not saturate even at very high applied fields, resulting in the short range magnetic order in the system, which facilitates the formation of clusters that freeze at low temperature.
Abstract: Systematic dc and ac magnetic susceptibility measurements performed on RuSr2Eu15Ce05Cu2O10−δ (Ru1222) demonstrate a paramagnetic to ferromagnetic transition around 95 K The third harmonic of the ac susceptibility reveals that the system undergoes a spin glass transition below 75 K The features of the zero-field cooled and field cooled dc magnetization curves of Ru1222 material resemble those of a cluster glass state, rather than those of a canonical spin glass state The magnetization versus applied field loops do not saturate, even at very high applied fields, resulting in the short range magnetic order in the system, which facilitates the formation of clusters that freeze at low temperature The temperature dependence of the second and third harmonic ac susceptibilities further confirms the coexistence of a cluster glass state and ferromagnetic order in the Ru1222 system
TL;DR: In this paper, an ionic liquid monomer was synthesized and polymerized into random copolymers and their ionic conductivity and structure were investigated as a function of copolymer composition.
Abstract: Ionic conductivity in new polymerized ionic liquids is of great interest as it applies to solid-state electrolytes for electrochemical and electromechanical applications. In this study, an ionic liquid monomer was synthesized and polymerized into random copolymers and their ionic conductivity and structure were investigated as a function of copolymer composition. Both nonionic−ionic and ionic−ionic copolymers were synthesized, where the nonionic and ionic monomers were hexyl methacrylate (HMA) and a methacrylate-based imidizolium neutralized with tetrafluoroborate (BF4) or bis(trifluoromethane sulfonyl)imide (TFSI). In the nonionic−ionic copolymer, the ionic conductivity increased by over an order of magnitude with increasing HMA composition, even though the overall charge content decreased, because the addition of HMA significantly lowered the glass transition temperature. The ionic conductivity also increased by more than an order of magnitude in the ionic−ionic copolymer with increasing TFSI content, e...
TL;DR: In this article, the effect of annealing on the bending ductility, the isoconfigurational elastic constants, the structure and the thermal stability of bulk metallic glasses was examined.
TL;DR: A DSC method was developed for measuring the solubility of crystalline drugs in polymers and has the potential of providing useful data for designing physically stable formulations of amorphous drugs.
Abstract: Amorphous pharmaceuticals, a viable approach to enhancing bioavailability, must be stable against crystallization. An amorphous drug can be stabilized by dispersing it in a polymer matrix. To implement this approach, it is desirable to know the drug’s solubility in the chosen polymer, which defines the maximal drug loading without risk of crystallization. Measuring the solubility of a crystalline drug in a polymer is difficult because the high viscosity of polymers makes achieving solubility equilibrium difficult. Differential Scanning Calorimetry (DSC) was used to detect dissolution endpoints of solute/polymer mixtures prepared by cryomilling. This method was validated against other solubility-indicating methods. The solubilities of several small-molecule crystals in polymers were measured for the first time near the glass transition temperature, including d-mannitol (β polymorph) in PVP, indomethacin (γ polymorph) in PVP/VA, and nifedipine (α polymorph) in PVP/VA. A DSC method was developed for measuring the solubility of crystalline drugs in polymers. Cryomilling the components prior to DSC analysis improved the uniformity of the mixtures and facilitated the determination of dissolution endpoints. This method has the potential of providing useful data for designing physically stable formulations of amorphous drugs.
TL;DR: The elastic modulus of a series of poly(methacrylate) films with widely varying bulk T(g)'s as a function of thickness at ambient temperature is measured, exploiting a wrinkling instability of a thin, stiff film on an thick, elastic substrate.
Abstract: Understanding the mechanical properties of polymers at the nanoscale is critical in numerous emerging applications. While it has been widely shown that the glass transition temperature (Tg) in thin...
TL;DR: In this article, single-walled carbon nanotubes (SWCNTs) were used to construct poly(ether ether ketone) based composites using melt processing.
TL;DR: In this article, the effect of unmodified multilayer carbon nanotubes (MWNTs) on the cure behavior of an epoxy resin was investigated and it was found that the cure reaction was promoted in its early stage which may be due to the catalyst particles present in CNT raw material.
Abstract: Motivated by the widespread and contradictory results regarding the glass transition temperature of carbon nan- otube (CNT)/epoxy composites, we reviewed and analyzed the literature results dealing with the effect of unmodified mul- tiwall carbon nanotubes (MWNT) on the cure behaviour of an epoxy resin (as a possible source of this discrepancy). The aim of this work was to clarify the effective role of unmodified multiwall carbon nanotubes on the cure kinetics and glass transition temperature (Tg) of their epoxy composites. It was found that various authors reported an acceleration effect of CNT. The cure reaction was promoted in its early stage which may be due to the catalyst particles present in the CNT raw material. While SWNT may lead to a decrease of Tg due to their bundling tendency, results reported for MWNT suggested an increased or unchanged Tg of the composites. The present status of the literature does not allow to isolate the effect of MWNT on the Tg due to the lack of a study providing essential information such as CNT purity, glass transition tempera- ture along with the corresponding cure degree.
TL;DR: In this article, a spray drying trial was carried out to produce amorphous powder from pure sucrose solutions and spray drying at inlet and outlet temperatures of 160 degrees C and 70 degrees C, respectively.
TL;DR: The segmental and local dynamics as well as the transport of Li(+) cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content are investigated, using dielectric relaxation spectroscopy.
Abstract: We investigate the segmental and local dynamics as well as the transport of Li(+) cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content, using dielectric relaxation spectroscopy. We observe a slowing down of segmental dynamics and an increase in glass transition temperature above a critical ion content, as well as the appearance of an additional relaxation process associated with rotation of ion pairs. Conductivity is strongly coupled to segmental relaxation. For a fixed segmental relaxation frequency, molar conductivity increases with increasing ion content. A physical model of electrode polarization is used to separate ionic conductivity into the contributions of mobile ion concentration and ion mobility, and a model for the conduction mechanism involving transient triple ions is proposed to rationalize the behavior of these quantities as a function of ion content and the measured dielectric constant.