Polymer Segmental Motion Research Articles

Ion Transport Study in CS: POZ Based Polymer Membrane Electrolytes Using Trukhan Model.

In this work, analysis of ion transport parameters of polymer blend electrolytes incorporated with magnesium trifluoromethanesulfonate (Mg(CF3SO3)2) was carried out by employing the Trukhan model. A solution cast technique was used to obtain the polymer blend electrolytes composed of chitosan (CS) and poly (2-ethyl-2-oxazoline) (POZ). From X-ray diffraction (XRD) patterns, improvement in amorphous phase for the blend samples has been observed in comparison to the pure state of CS. From impedance plot, bulk resistance (Rb) was found to decrease with increasing temperature. Based on direct current (DC) conductivity (σdc) patterns, considerations on the ion transport models of Arrhenius and Vogel–Tammann–Fulcher (VTF) were given. Analysis of the dielectric properties was carried out at different temperatures and the obtained results were linked to the ion transport mechanism. It is demonstrated in the real part of electrical modulus that chitosan-salt systems are extremely capacitive. The asymmetric peak of the imaginary part (Mi) of electric modulus indicated that there is non-Debye type of relaxation for ions. From frequency dependence of dielectric loss (ε″) and the imaginary part (Mi) of electric modulus, suitable coupling among polymer segmental and ionic motions was identified. Two techniques were used to analyze the viscoelastic relaxation dynamic of ions. The Trukhan model was used to determine the diffusion coefficient (D) by using the frequency related to peak frequencies and loss tangent maximum heights (tanδmax). The Einstein–Nernst equation was applied to determine the carrier number density (n) and mobility. The ion transport parameters, such as D, n and mobility (μ), at room temperature, were found to be 4 × 10−5 cm2/s, 3.4 × 1015 cm−3, and 1.2 × 10−4 cm2/Vs, respectively. Finally, it was shown that an increase in temperature can also cause these parameters to increase.

On the Relation between Ionic Transport Properties and Viscoelastic Response of Solid Polymer Electrolytes

The need for high energy density and micro-scaled power sources is pushing researchers and industries towards the development of three-dimensional architecture micro-batteries and structural batteries. In this perspective, solid polymer electrolytes (SPEs) represents an appealing alternative to conventional (liquid) electrolyte. Due to their intrinsic multifunctionality, SPEs can serve as the structural matrix of fiber-reinforced composites and as the electrolyte of a battery. In addition, the improved safety features, excellent flexibility and processability, allow to cast SPEs into complex three-dimensional geometries without leakage. Experimental studies indicate that mechanical and electrochemical responses of SPEs are related. In particular, the segmental motion of the polymer molecules is crucial for both the viscoelastic properties and the ionic conductivity of the material. A limited polymer segmental motion generally results in a stiffer mechanical response and a reduced ionic conductivity, while the opposite applies when the polymer segmental motion is enhanced. This results in a trade-off between mechanical and electrical performance from a material design point of view [1] and a deformation-dependent ionic transport mechanism in the polymer during service [2]. In this work we present a coupled electrochemo-mechanical model for SPEs. The polymer is modeled as a solid through which the transport of multiple charged species takes place and is described in terms of molar concentration of ions, electric potential and displacement field. Since the molar concentration of ions in the SPE is notably non-uniform during battery service [3,4], the model explicitly accounts for concentration-dependent diffusion coefficients and viscoelastic properties. Results of a finite element method formulation are presented, and the impact of the viscoelastic mechanical behavior on the overall battery response is discussed.

Functionalized Silica Particle Based Single Ion Conducting Hybrid Electrolyte for Li-Ion Battery

For advanced energy storage (batteries and supercapacitors), energy conversion (fuel cells and solar cells), and electromechanical transduction devices (electroactive ionic actuators and sensors), it is vital to utilize single-ion polymer conductors (ionomers) that have been designed by covalently attaching anions (or cations) to the polymer chains. This allows the high lithium transference number in lithium polymer batteries as well as the fast response time under low voltage operating conditions in ionic polymer actuators. However, current single-ion conductors exhibit relatively low conductivities, precluding use of these materials in potential applications. This is predominantly due to relatively slow polymer segmental motion, resulting in decreased ion mobility, and large ion dissociation energy, lowering the number of simultaneous charge carries. In order to overcome the issues, we have synthesized porous silica-based lithium single-ion conducting nanoparticles containing anions with lithium counter ions. These nanoparticles are then introduced into poly(ethylene oxide) matrix, allowing us to prepare nanocomposite polymer electrolytes. Anion functionalized mesoporous silica (FMS-TFSISPE) nanoparticles were prepared by the two-step selective functionalization method. Poly(ethylene glycol) group was attached using sol-gel method on mesoporous silica particles. Trifluoromethanesulfonimide group functionalized to silica particles for binding lithium cation. The particles are uniformly distributed with an average size of 50 nm. HRTEM measurement further suggests that the clear mesoporous structure is observed. In order to extensively investigate the structural information on FMS-TFSISPE, the N2 adsorption/desorption isotherm is obtained as shown, where FMS-TFSISPE shows type IV isotherms of typical mesoporous materials, and the BET surface area is 995 m2 g- 1. The average pore size of the FMS-TFSISPE nanoparticles is about 3 nm which is close to that observed by the HRTEM measurement. The small angle XRD analysis shows three resolved peaks from which the pore structure corresponds to a 2D hexagonal (P6mm) structure. From the structure analysis, we successfully synthesized the FMS-TFSISPE nanoparticles with well-ordered hexagonal arrays of mesopore channels and exceptionally high surface area and pore volume. It is apparent that FMS-TFSISPE nanoparticles have a considerable effect on the enhancement of the ionic conductivity of these electrolytes, and their conductivities increase monotonically with increasing FMS-TFSISPE content. The maximum enhancement in conductivity is found for the nanohybrid electrolyte containing 30 wt % FMS-TFSISPE and order of sDC ~ 10- 3 S/cm at 25 oC, 10 times higher than the minimum practical requirement for single-ion conductors. We develop a novel nanohybrid single-ion conductor based porous silica structure. These systems display exceptional ionic conductivity and lithium transference number. It is shown that such nanohybrid electrolytes significantly immobilize the anion movement and pave the way for fast lithium ion-only conducting pathway. Provided that the optimization of the nanohybrid electrolytes with high-energy and -power electrodes is realized, the use of our highly conducting single-ion conductor in practical polymer electrolyte batteries will be envisaged.

Investigation of the free volume characteristics of PEO based solid state polymer electrolyte by means of positron annihilation spectroscopy

Ion conduction in poly (ethylene oxide), PEO, based electrolytes are explained considering the ion movement coupled with polymer segmental motions or free volume. Herein, we describe the application of positron annihilation spectroscopy to investigate the free volume structure of PEO-LiTFSI solid state electrolyte with varying electrolyte concentration. Addition of LiTFSI indicates plasticization effect through the increase in free volume size of polymer matrix. Depth dependent Doppler broadening measurements have shown a decrease in positron/positronium diffusion length and S-parameter value on addition of electrolyte. The observed decrease in S-parameter and positronium intensity could not be ascribed to positronium reaction (inhibition) with dissociated ions or salt aggregates as the variation does not follow the established inhibition expression. The SW correlation curves indicate that the chemical environment at positron/positronium annihilation sites in PEO-LiTFSI is similar to pristine PEO. It again confirms that reduction in positronium intensity and S-parameter cannot be attributed to positronium inhibition. The present study shows that resultant positron/positronium annihilation parameters can be directly attributed to the change in molecular packing or free volume structure of the solid state electrolytes.

Monodisperse and Telechelic Polyethylenes Form Extended Chain Crystals with Ionic Layers

We report the synthesis of ionic telechelic low-molecular-weight polyethylenes (PEs) with precise chain lengths that are derived from plant oils along with their morphologies and temperature-dependent ionic conductivities. Starting from the C48 telechelic dimethyl ester, or the C23 analogue for comparison, different ionic carboxylate end groups (H+, Na+, Cs+, Zn2+) were introduced by microwave-assisted saponification chemistry. Because of the precise length of the polymethylene sequence, these difunctional telechelic PEs crystallize into exceptionally well-ordered nanoscale-layered structures at room temperature. As a consequence of their extended chain crystal nature, the layer thickness is directly encoded by the telechelic molecules methylene chain length. Notably, C21(COONa)2, C46(COONa)2, and C46(COOCs)2 exhibit transitions in the crystalline structure prior to the fully disordered melt state, as evidenced by differential scanning calorimetry and in situ X-ray scattering. The melting transition is typically accompanied by a transition from layered ionic nanoaggregates between the crystallites to disordered ionic aggregates, with an interesting exception wherein the ionic layers transform to hexagonal symmetry. The temperature-dependent ionic conductivities of layered crystalline morphologies in the C48 materials exhibit an Arrhenius-like behavior, indicating a decoupling from the slower polymer segmental motions at T < Tm. These new precise ionic telechelic PEs produce well-defined nanoscale-layered morphologies with tunable ion transport properties that could be further developed as solid-state electrolytes.

Superior charge discharge ability of reduced graphene oxide/Li-ion embedded polymer composite films

Electroactive polymeric composites are recent generation material for energy application in lithium batteries, solar cells and supercapacitors. In present study, reduced graphene oxide is prepared from graphite powder using liquid exfoliation. The synthesized reduced graphene oxide is embedded with polystyrene sulfonic acid/lithium phosphate polymer electrolyte to obtain polymer composite films. The dielectric studies of composite reveals huge change in relaxation time with addition of rGO in polymeric lithium ion composites. This attributes to decrease in ion-dipolar interaction strength and enhanced polymer segmental motion in presence of carbon. It also implies the activation of electrochemical properties of polystyrene sulfonic acid/lithium phosphate/reduced graphene oxide (PL–rGO) composites which can be effectively utilize for charge storage applications. The PL–rGO composite exhibits an improved electrochemical performance with different scan rate on potential window ranged between − 0.5 and 1.2 V. The specific capacitance value of ~ 17 F/g with high rate charge–discharge capability over 8000 cycles was observed. Higher electrochemical stability and steady charge/discharge behavior makes PL–rGO composites a promising candidate for charge storage applications.

Structural, electrical and dielectric studies of nano-composite polymer blend electrolyte films based on (70–x) PVA–x PVP–NaI–SiO2

Nano-composite polymer electrolytes (NCPEs) films based on PVA-PVP-NaI-SiO2 have been prepared using solution casting technique. Investigation of prepared films have been made using various experimental techniques like x-ray diffraction (XRD), attenuated total reflection–fourier transform infrared (ATR-FTIR), differential scanning calorimetric (DSC) and ac impedance spectroscopy. XRD determines the structural properties and shows the significant variation in the characteristic peaks related to semi-crystalline/amorphous phase of different PVA-PVP polymer blend ratio for fixed loading of NaI and SiO2. Complexation of PVA-PVP polymer blend with NaI and SiO2 has been confirmed by ATR–FTIR analysis. Variation in glass transition temperature (Tg) and melting temperature (Tm) of PVA-PVP-NaI-SiO2 NCPE system having various concentration of PVP were observed by DSC analysis. It has been observed that ac conductivity spectra strongly obeys the Jonscher's universal power law [σ=σdc+Afn] with power exponent, n < 1. The dielectric permittivity (ε′&ε″) and electric modulus (M′&M″) measurements were performed in a wide frequency range (10 mHz-10 MHz). Variation of conductivity with temperature shows that the ion conduction and polymer segmental motions are closely related and are governed by Arrhenius mechanism. A couple of peaks observed in loss tangent (tan δ) shows two types of relaxation processes interpreted in terms of dipole segmental motion (α-relaxation) and side chain dipole group motion (β-relaxation).

(Invited) Polymer Simulations Under External Fields

In order to design next generation functional polymers, not only the structure but the dynamics under external field should be understood. In this paper we report our simulation approach to investigate the structure and dynamics. Polymer brush is used for the model system of very low friction such as synovial joints. Recently, polymer brush is focused as a functional binder of sodium ion secondary battery. Since sodium ions are hard to make passive film, or SEI (solid electrolyte interphase) layer on the negative electrode, functional polymer binder help to stabilize the atmosphere around the electrode. We simulate the ionic conductivity of polyelectrolyte binder system under external electric field. The conductivity depend on the polymer structure, such as hardness and linear charge density of the polymer chain. The other important function of polymers are the fluid dynamics effect of polymers under external fluid field. As a model system of VII (viscosity index improver) polymers, we simulate the dynamics under shear filed. The dynamics of polymers are studied for bulk system and the confined system. We made simulation algorithm. The Brownian motion of polymer segments are treated by Langevin Dynamics, and the solvent flow is treated by Lattice Boltzmann Method, in order to obtain both high computational efficiency and precise dynamics. We succeed to reproduce the flow dynamics of polymers under shear. Moreover, the model is extended to include long-range interactions of functional groups. In low dielectric constant medium such as lubricant oils, the functional groups interact as ionic groups in high dielectric constant medium such as waters. The specific results shows that the colloidal science in oils have many problems to be solved.

Interfacial Diffusion of Silver Nanocrystals into Polymer Surfaces Monitored by Hybrid Plasmon Modes

Functional response of polymer–nanoparticle nanocomposites depend strongly on physical organization and interactions between constituting components. In this work, we study thermally induced embedding of silver nanocrystals (nanocubes, AgNC) into different polymer films to probe the interfacial nanoparticle diffusion dynamics and to determine temperature of embedding (Te) into the polymer substrates. The spatial sensitivity of the AgNCs hybrid plasmonic modes allowed the detection of a thin layer on top of the polymer film with increased polymer segmental motion and Te lower than the glass transition temperature Tg of the bulk polymer. Utilizing supported AgNCs as a nanoruler, diffusion constants of the nanocubes embedding into thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and polyvinyl chloride (PVC) were determined, and an Arrhenius temperature dependence on the diffusion constants was observed. The activation energies for the AgNCs embedding into the polymers were found to be 220 ± ...

Nuclear Magnetic Resonance Investigations of a Next-Generation Battery Lithium Polymer Electrolyte

The Li-ion battery has served as the workhorse of many industries for a generation. The technology has advanced incrementally over the years, but the underlying chemistry has undergone only minimal changes since its commercialization in the early 90’s. A novel solvent-free polymer electrolyte developed by Ionic Materials, Inc. threatens to shift this paradigm. The polymer electrolyte is based on a crystalline thermoplastic polymer which is treated with an oxidizing agent and then reacted with a lithium salt. This electrolyte displays transport properties suitable for commercial battery use, while retaining the mechanical and safety advantages associated with a solid, and sufficient electrochemical stability to allow its use with Li-metal and high voltage intercalation electrodes. We report here Nuclear Magnetic Resonance (NMR) investigations of this polymer electrolyte. Pulsed-field gradient self-diffusion studies, in tandem with relaxometry and magic angle spinning (MAS), allow characterization of the structure and dynamics of this revolutionary material. Our measurements show room-temperature Li+ self-diffusion coefficients on the order of 10-9 m2/s (an order of magnitude higher than previously reported solid electrolyte candidates), as well as cation transference numbers approaching 0.5. We have also established further evidence that the ionic motion is decoupled from polymer segmental or chain motion, in contrast to the mechanism governing ionic transport in the widely studied polyether-based electrolytes. We discuss some of the challenges of studying this material, as well as the implications of the results for its suitability as an electrolyte for secondary Li metal batteries.

Fabrication of Li-Polymer/Silica Aerogel Nanocomposite Electrolyte for an All-Solid-State Lithium Battery

The demand for solid-state lithium ion electrolytes has increased owing to the safety concerns regarding the use of lithium ion batteries, which contain flammable organic solvent electrolytes. The liquid electrolyte can give rise to serious problems such as leakage and gas explosions when the operating temperature rises. The use of an organic or inorganic solid electrolyte not only results in improved safety, but also facilitates the fabrication of miniature batteries using thin films. A solid electrolyte is required to have high lithium ion conductivity, mechanical strength, and transference number for lithium ions as well as good thermal/electrochemical stability and compatibility with the electrodes. Recently, polymer-based solid electrolytes have been widely studied for a possible replacement for liquid electrolytes. Various types of polymer-based solid electrolytes for lithium ion batteries exist, such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyvinylidene fluoride (PVDF). Among them, the PEO-based polymer has attracted considerable attention, owing to its flexible skeleton and good interfacial stability with lithium electrodes. The mechanism of lithium ion conduction in the PEO-based solid-polymer electrolyte involves the coordination of the lithium ion from the Li-salt by the ether oxygen from the PEO, which moves according to the polymer segmental motion. In this study, a polymer blend of PEO and PVDF, containing fluorine as a polar element, was fabricated to improve the dissociation degree of the Li-salt. In addition, we anticipate that the addition of ultra-porous silica aerogels, which has a high porosity and specific surface area, would increase the lithium ion conductivity. The silica aerogel was fabricated from water glass using the emulsion polymerization method, as was previously described by our research group. We also investigated the effects of the PEO:PVDF molar ratio, polymer:Li-salt molar ratio, and silica aerogel content on the structural, thermal, and electrical properties.

Non-constant link tension coefficient in the tumbling-snake model subjected to simple shear.

The authors of the present study have recently presented evidence that the tumbling-snake model for polymeric systems has the necessary capacity to predict the appearance of pronounced undershoots in the time-dependent shear viscosity as well as an absence of equally pronounced undershoots in the transient two normal stress coefficients. The undershoots were found to appear due to the tumbling behavior of the director u when a rotational Brownian diffusion term is considered within the equation of motion of polymer segments, and a theoretical basis concerning the use of a link tension coefficient given through the nematic order parameter had been provided. The current work elaborates on the quantitative predictions of the tumbling-snake model to demonstrate its capacity to predict undershoots in the time-dependent shear viscosity. These predictions are shown to compare favorably with experimental rheological data for both polymer melts and solutions, help us to clarify the microscopic origin of the observed phenomena, and demonstrate in detail why a constant link tension coefficient has to be abandoned.

Polyimide-SiO2-TiO2 nanocomposite structural study probing free volume, physical properties, and gas transport

Polyimide-SiO2-TiO2 nanocomposite membrane permeability, diffusivity, and selectivity were evaluated using polyimide block copolymers designed from 6F and [6F-DABA], and [SiO2-TiO2] using He, H2, CO2, O2, N2, and CH4. Nanocomposite membranes were synthesized using an in-situ sol-gel method to improve the integration of inorganic and organic phases. Metal alkoxide type and polymer functional groups were key factors affecting physical properties and gas transport. [6F-DABA]-[SiO2-TiO2] nanocomposite fractional free volume (FFV) increased 29% as compared to the unmodified [6F-DABA] polyimide. Dynamic Mechanical Thermal Analysis revealed that [SiO2-TiO2] and [TiO2] within functionalized multi-block reduced chain mobility. This led to a Tg increase from 334°C to 359°C, and tanδ to decrease from 1.9 to 0.35. In general, inorganic concentration and composition retarded polymer segmental motions, inhibited polymer chain packing, and increase predicted FFV. [6F-DABA-50]-[SiO2-TiO2] membrane's exhibited a simultaneous gas selectivity and permeability improvement. He permeability improved from 58 (unmodified polyimide) to 83 Barrers, and He/CH4 gas selectivity increased from 221 (unmodified) to 334. Membrane gas separation performance of several organic-inorganic materials exceeded Robeson's “upper bound.”

Thermal and dynamic mechanical thermal analysis of lignocellulosic material-filled polyethylene bio-composites

Thermal and rheological properties of plant-based natural filler-reinforced polyethylene bio-composites applying various filler loadings as well as the impacts of the different compatibilizers were investigated by means of differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA). As lignocellulosic materials, such as rice-husk flour and wood flour, are eco-friendly biomaterials and a thermoplastic polymer, for example, high-density polyethylene, has good physico-mechanical and thermal properties, therefore their bio-composites can combine and utilize these two advantages at the same time. The temperature of the α-relaxation (T α) slightly increased and melting temperatures (T m) of the matrix polymer in the case of the studied bio-composites did not shift significantly as the filler loading changed, because the rigid interphase hinders the motion of polymer segments resulting in the increase in T α and only weak interactions developed at the interface between the matrix polymer and the reinforcement in the case of non-compatibilized composites. However, compatibility between the reinforcement and the matrix polymer was enhanced by incorporating compatibilizers, which further improved stiffness. From the DMTA experiment, the reinforcements result in composite samples having higher storage modulus (E′) than the neat polymer sample, indicating that incorporating lignocellulosic filler increased their stiffness.

Decoupling of ion conductivity from segmental dynamics in oligomeric ethylene oxide functionalized oxanorbornene dicarboximide homopolymers

In order to design more effective solid polymer electrolytes, it is important to decouple ion conductivity from polymer segmental motion. To that end, novel polymers based on oxanorbornene dicarboximide monomers with varying lengths of oligomeric ethylene oxide side chains have been synthesized using ring opening metathesis polymerization. These unique polymers have a fairly rigid and bulky backbone and were used to investigate the decoupling of ion motion from polymer segmental dynamics. Ion conductivity was measured using broadband dielectric spectroscopy for varying levels of added lithium salt. The conductivity data demonstrate six to seven orders of separation in timescale of ion conductivity from polymer segmental motion for polymers with shorter ethylene oxide side chains. However, commensurate changes in the glass transition temperatures Tg reduce the effect of decoupling in ion conductivity and lead to lower conductivity at ambient conditions. These results suggest that both an increase in decoupling and a reduction in Tg might be required to develop solid polymer electrolytes with high ion conductivity at room temperature.

Fundamental aspects of electrochemically controlled wetting of nanoscale composite materials.

Electroactive films based on conducting polymers have numerous potential applications, but practical devices frequently require a combination of properties not met by a single component. This has prompted an extension to composite materials, notably those in which particulates are immobilised within a polymer film. Irrespective of the polymer and the intended application, film wetting is important: by various means, it facilitates transport processes - of electronic charge, charge-balancing counter ions ("dopant") and analyte/reactant molecules - and motion of polymer segments. While film solvent content and transfer have been widely studied for pristine polymer films exposed to molecular solvents, extension to non-conventional solvents (such as ionic liquids) or to composite films has been given much less attention. Here we consider such cases based on polyaniline films. We explore two factors, the nature of the electrolyte (solvent and film-permeating ions) and the effect of introducing particulate species into the film. In the first instance, we compare film behaviours when exposed to a conventional protic solvent (water) with an aprotic ionic liquid (Ethaline) and the intermediate case of a protic ionic liquid (Oxaline). Secondly, we explore the effect of inclusion of physically diverse particulates: multi-walled carbon nanotubes, graphite or molybdenum dioxide. We use electrochemistry to control and monitor the film redox state and change therein, and acoustic wave measurements to diagnose rheologically vs. gravimetrically determined response. The outcomes provide insights of relevance to future practical applications, including charge/discharge rates and cycle life for energy storage devices, "salt" transfer in water purification technologies, and the extent of film "memory" of previous environments when sequentially exposed to different media.

Molecular Dynamics Study of a Dual-Cation Ionomer Electrolyte.

The poly(N1222 )x Li1-x [AMPS] ionomer system (AMPS=2-acrylamido-2-methylpropane sulfonic acid) with dual cations has previously shown decoupled Li ion dynamics from polymer segmental motions, characterized by the glass-transition temperature, which can result in a conductive electrolyte material whilst retaining an appropriate modulus (i.e. stiffness) so that it can suppress dendrite formation, thereby improving safety when used in lithium-metal batteries. To understand this ion dynamics behavior, molecular dynamics techniques have been used in this work to simulate structure and dynamics in these materials. These simulations confirm that the Li ion transport is decoupled from the polymer particularly at intermediate N1222+ concentrations. At 50 mol % N1222+ concentration, the polymer backbone is more rigid than for higher N1222+ concentrations, but with increasing temperature Li ion dynamics are more significant than polymer or quaternary ammonium cation motions. Herein we suggest an ion-hopping mechanism for Li+ , arising from structural rearrangement of ionic clusters that could explain its decoupled behavior. Higher temperatures favor an aggregated ionic structure as well as enhancing these hopping motions. The simulations discussed here provide an atomic-level understanding of ion dynamics that could contribute to designing an improved ionomer with fast ion transport and mechanical robustness.

Heterogeneity during Plasticization of Poly(vinylpyrrolidone): Insights from Reorientational Mobility of Single Fluorescent Probes.

While dynamics of single-molecule (SM) fluorescent probes have been used to investigate the structure and relaxation processes in polymers near the glass transition temperature (Tg), it is difficult to perform SM imaging at elevated temperatures which restricts such studies to a limited number of polymers for which Tg is close to room temperature (RT). Plasticization, solvent (or additive) induced lowering of Tg, offers an alternate avenue to access various effective temperatures in the glassy and rubbery phases of polymers under ambient conditions. By investigation of the reorientational propensity of individual Rhodamine 6G (Rh6G) probes, which is governed by rigidity/dynamics of the polymer cavities, we have explored the extent of spatiotemporal heterogeneity during moisture induced plasticization of poly(vinylpyrrolidone) (PVP), far below and near (below and above) bulk Tg. Lack of any probe reorientation suggests that the matrix remains extremely rigid up to a certain level of hydration, as expected for probes buried deep within the glassy state. At intermediate levels of hydration, SMs undergo a wide variety of rotational dynamics ranging from being static/wobbling motion to slow, hindered large-angle reorientation, as well as facile, intermittently hindered fast rotation, which reflects that swelling/softening of network cavities is spatiotemporally extremely diverse as the effective Tg approaches RT. SM probes exhibit temporally nonuniform rotational mobility even at relatively high moisture contents of the matrix beyond which probes can undergo translational motion, which indicates that relatively slow time scale polymer segmental motion can be operational for plasticized PVP (in the rubbery state). Our inferences are supported by the non-Gaussian nature of angular jump distributions for dipolar reorientation, similar to those reported for translational diffusion of SM tracers in polymers and cellular media, suggesting the existence of slow time-varying local environmental changes around individual probe molecules during plasticization.

Diffusive Flux as a New Metric for Ion-Conducting Soft Materials

7Li NMR diffusion measurements for single-ion conducting ionomers with strong solvation for lithium reveal that diffusion is considerably faster than expected from ionic conductivity measurements, suggesting that neutral ion pairs dominate lithium transport in this class of materials. Ion aggregation is controlled by the overlap parameter for ion pair polarizability volumes; at ion contents higher than the polarizability volume overlap threshold, ion pairs aggregate strongly, making the dielectric constant saturate and the glass transition temperature increase more rapidly with ion content. Neutral ion pairs hop from one aggregate to a neighboring one by polymer segmental motion. Only when the ion pair has an extra lithium (i.e., a positive triple ion) do such hops contribute to ionic conductivity.

Effect of relaxation processes during deformation on electrical resistivity of polyethylene composites filled with carbon black

This work is dedicated to the study of the influence of the deformation and relaxation processes on electrical resistivity of polyethylene composites filled with carbon black. It was shown that bending deformation of specimens, in particular at elevated temperatures, leaded to the reversible change in electrical resistivity. Obtained results imply relationship between electrical relaxation and mechanical relaxation conditioned by segmental motion of polymers.