Transport Properties Of Poly Research Articles

Structure and Transport Properties of Poly(ethylene oxide)-Based Cross-Linked Polymer Electrolytes─A Molecular Dynamics Simulations Study

We present an extensive molecular dynamics (MD) simulation study of poly(ethylene oxide) (PEO) based densely cross-linked polymers, focussing on structural properties as well as the systems dynamics in the presence of lithium salt. Motivated by experimental findings for networks with short PEO strands we employ a combination of LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide) and LiDFOB (Lithium difluoro(oxalato)borate). Recently, it has been shown that such multi-salt systems outperform classical single salt systems (Shaji et al., Energy Storage Materials, 2022, 44, 263). To analyse the microscopic scenario we employ an analytical model, originally developed for non-cross-linked polymer electrolytes or blends (Maitra et al., Phys. Rev. Lett., 2007, 98, 227802 and Diddens et al., J. Electrochem. Soc., 2017, 164, E3225-E3231). Excluding very short PEO strands, the local dynamics is only slightly restricted compared to linear PEO and is not significantly dependent on the network structure. The transfer of lithium ions between PEO chains and the motion along the polymer backbone may be controlled through the employed salt.

Dynamical Ion Association and Transport Properties in PEO-LiTFSI Electrolytes: Effect of Salt Concentration.

The association of ions describes the formation of ion species in electrolyte solutions and is strongly related to the salt concentration. However, the discussion of ion species and their transport is ambiguous in some studies on electrolyte materials due to the assumption of ideal solutions. Accordingly, in this work, molecular dynamics simulations are used to study ion association and transport properties of poly(ethylene)oxide (PEO)-lithium bis(trifluoromethanesulfonyl)imide electrolytes over a range of salt concentrations (r = [Li]/[EO]) from 0.01 to 0.20. Based on the analysis of the solvation environment and ion species, it is revealed that the distinct ion-ion correlations exist in two different characteristic areas, with a salt concentration of 0.10 as the limit. Below the critical concentration, the dynamic equilibrium between free ions and ion pairs is the most important process affecting the transport properties of electrolytes, but the process may have a minor influence on the applicability of the Nernst-Einstein relation. In concentrated solutions, a large number of ion pairs, triplets, and so forth appear in the electrolytes. The high-order ion clusters, with an average size of 3.95 at r = 0.20, are the main stable structures for transporting Li+, but the trapped free ions are the most abundant ion species. Meanwhile, the effect of salt concentrations on the average transport of ion clusters is to increase their average lifetime, but their transport rates remain unchanged. In addition, the coupling dynamics between ions and polymers is also discussed in order to gain a complete insight into the importance of salt concentrations.

The transport properties of poly(G)-poly(C) DNA oligomers in the Harrison's model

Using the tight-binding Hamiltonian of the Harrison's model and the Landauer-Büttiker formalism, some of the electron transport properties of short poly(G)-poly(C) DNA segments lying between two semi-infinite carbon chains as the nanoleads are investigated. The analytical results of the self-energies due to the leads are represented by solving the discretized form of the one-dimensional Schrödinger's equation. Under the Harrison's model, with considering in-phase overlap between the nearest neighbors' all kinds of atomic orbitals, the influences of more atomic orbitals in central channel and backbone of DNA (according to Fishbone model) on the electron transmission probability are discussed. Transmission probabilities for both the single- and many-orbital states are calculated and compared with each other. Furthermore, the effect of increasing length of the DNA nanowire and the coupling strength of nanolead/DNA interface on transmission probability and the current-voltage (I–V) curves and also the effect of different temperatures of the leads on the I–V characteristics are studied. Our results show that the poly(G)-poly(C) DNA oligomer exhibits a semiconducting behavior and that the vertical coupling strength between base pairs and the sugar-phosphate backbone in poly(G)-poly(C) DNA structure can induce the semiconducting gap.

The role of coordination strength in solid polymer electrolytes: compositional dependence of transference numbers in the poly(ε-caprolactone)-poly(trimethylene carbonate) system.

Both polyesters and polycarbonates have been proposed as alternatives to polyethers as host materials for future polymer electrolytes for solid-state lithium-ion batteries. While being comparatively similar functional groups, the electron density on the coordinating carbonyl oxygen is different, thereby rendering different coordinating strength towards lithium ions. In this study, the transport properties of poly(ε-caprolactone) and poly(trimethylene carbonate) as well as random copolymers of systematically varied composition of the two have been investigated, in order to better elucidate the role of the coordination strength. The cationic transference number, a property well-connected with the complexing ability of the polymer, was shown to depend almost linearly on the ester content of the copolymer, increasing from 0.49 for the pure poly(ε-caprolactone) to 0.83 for pure poly(trimethylene carbonate). Contradictory to the transference number measurements that suggest a stronger lithium-to-ester coordination, DFT calculations showed that the carbonyl oxygen in the carbonate coordinates more strongly to the lithium ion than that of the ester. FT-IR measurements showed the coordination number to be higher in the polyester system, resulting in a higher total coordination strength and thereby resolving the paradox. This likely originates in properties that are specific of polymeric solvent systems, e.g. steric properties and chain dynamics, which influence the coordination chemistry. These results highlight the complexity in polymeric systems and their ion transport properties in comparison to low-molecular-weight analogues, and how polymer structure and steric effects together affect the coordination strength and transport properties.

Molecular dynamics and Monte Carlo simulation of the structural properties, diffusion and adsorption of poly (amide-6-b-ethylene oxide)/Faujasite mixed matrix membranes

Molecular simulation has been undertaken to study the structural and transport properties of Poly (amide-6-b-ethylene oxide) (PEBA 1657)/Faujasite (FAU) mixed matrix membranes. Membranes were built with different amounts of FAU nanomaterials to investigate the influence of nanomaterial content on the membrane performances. Structural characterizations such as ractional free volume (FFV), radial distribution function (RDF), wide angle XRD (WAXD) and glass transition temperature were done on the simulated membrane cells to study their structural properties. Also, by using MSD and adsorption isotherms, diffusivity and selectivity of these membranes were measured, respectively. The two main transport factors (permeability and permselectivity) were examined using calculated diffusivity and solubility, and the membrane properties were investigated at two different operating temperatures (298K, 318K). Results show that by increasing the nanomaterials content, structural properties improve and transport properties increase which is due to the increase of the pathways for penetrant molecules to move through the membranes. Compared to the published results, the current simulation study is more accurate in describing the structural and transport properties of PEBA/FAU mixed matrix membranes. It was found that increasing the FAU content from 0 to 20wt% increased the permeability of the membrane to CO2, as well as the permselectivity for CO2/NO2 from 69.4 barrer to 89.23 barrer at 298K. This change in FAU content also decreased the glass transition temperature from 212K to 204.1K.

Structure and mechanisms underlying ion transport in ternary polymer electrolytes containing ionic liquids.

We use all atom molecular dynamics simulations to investigate the influence of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) ionic liquid on the structure and transport properties of poly(ethylene oxide) (PEO) polymer electrolytes doped with LiPF6 salt. We observe enhanced diffusivities of the Li+, PF6-, and BMIM+ ions with increasing loading of the ionic liquid. Interplay between the different ion-ion and ion-polymer interactions is seen to lead to a destabilization of the Li-PF6 coordination and increase in the strength of association between the Li+ cations and the polymer backbone. As a consequence, the polymer segmental relaxation times are shown to be only moderately affected by the addition of ionic liquids. The ionic-liquid induced changes in the mobilities of Li+ ions are seen to be correlated to polymer segmental relaxation times. However, the mobilities of BMIM+ ions are seen to be more strongly correlated to the BMIM-PF6 ion-pair relaxation times.

Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance.

Field-effect mobility of a polymer semiconductor film is known to be enhanced when the gate dielectric interfacing with the film is weakly polarizable. Accordingly, gate dielectrics with lower dielectric constant (k) are preferred for attaining polymer field-effect transistors (PFETs) with larger mobilities. At the same time, it is also known that inducing more charge carriers into the polymer semiconductor films helps in enhancing their field-effect mobility, because the large number of traps presented in such a disorder system can be compensated substantially. In this sense, it may seem that employing higher k dielectrics is rather beneficial because capacitance is proportional to the dielectric constant. This, however, contradicts with the statement above. In this study, we compare the impact of the two, i.e., the polarizability and the capacitance of the gate dielectric, on the transport properties of poly[(diketopyrrolopyrrole)-alt-(2,2'-(1,4-phenylene)bisthiophene)] (PDPPTPT) semiconductor layers in an FET architecture. For the study, three different dielectric layers were employed: fluorinated organic CYTOP (k = ∼2), poly(methyl methacrylate) (k = ∼4), and relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (k = ∼60). The beneficial influence of attaining more carriers in the PDPPTPT films on their charge transport properties was consistently observed from all three systems. However, the more dominant factor determining the large carrier mobility was the low polarizability of the gate dielectric rather than its large capacitance; field-effect mobilities of PDPPTPT films were always larger when lower k dielectric was employed than when higher k dielectric was used. The higher mobilities obtained when using lower k dielectrics could be attributed to the suppressed distribution of the density of localized states (DOS) near the transport level and to the resulting enhanced electronic coupling between the macromolecules.

Ionic conductivity and transport properties of poly(vinylidene fluoride-co-hexafluoropropylene)-based solid polymer electrolytes

Polymer electrolytes containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and various concentrations of lithium triflate were prepared to determine the optimal polymer-salt composition for maximum ionic conductivity. Complex formation was ascertained from X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) studies. The conductivity measurements reveal that the ionic conductivity of the polymer electrolytes containing various salt concentrations increases with temperature and obeys the Arrhenius rule. It is found that the electrolyte containing 25wt.% of lithium triflate exhibits the highest room temperature conductivity. Moreover, Ionic transference measurements show predominance of ionic motion.

Molecular dynamics approach to the structural characterization and transport properties of poly(acrylonitrile)/N,N-dimethylformamide solutions

Poly(acrylonitrile) (PAN) in N,N-dimethylformamide (DMF) is a popular solution for producing large variety of polymer products. To precisely describe the behaviours of PAN and DMF in the synthesis processes, it is significant to call for more details about the structure, some thermodynamic and dynamical properties of PAN-DMF solutions. A PAN-DMF solution was simulated via molecular dynamics with an all-atom OPLS type potential in both the NPT and NVT ensembles. The simulation results were evaluated with quantum mechanical calculations (MP2/6-311++G(d,p) and counterpoise procedure) and were compared with available experimental results. The liquid structure was illustrated with pair correlation functions and transport and dynamics properties were calculated with the mean-square displacements MSD and the velocity autocorrelation functions. The strong H-bonds of CN⋯HCO, CH⋯OCH and CH2⋯OCH, with distances of 2.55Å, 2.55Å and 2.65Å, respectively, were found. The largest interaction energy of −7.157kcal/mol between DMF molecules and PAN molecules was found at 4.9Å center-of-mass distance. A potential profile of intermolecular interaction of DMF with PAN along the interaction distance was presented, clearly showing an increase of DMF vaporisation heat when it getting close to PAN molecules. This provided very useful information to analyse the vaporisation behaviours of DMF at the microscopic level, which is essential to comprehensively understand molecular rearrangements towards the design of synthetic processes. The impact of the presence of the PAN on the DMF solution properties were also benchmarked with pure DMF solution.

Gas transport properties of reverse-selective poly(ether-b-amide6)/[Emim][BF4] gel membranes for CO2/light gases separation

The present research investigates deeply the effect of 1-ethyl-3 methylimidazolium tetrafluoroborate ([Emim][BF4]) ionic liquid on separation performance and transport properties of poly(ether-b-amide6) (Pebax1657) at different operating pressures from 2 to 20bar and temperatures from 25 to 65°C. [Emim][BF4] showed interesting separation factor for CO2/light gases as a solvent and it was expected that its addition to Pebax1657 leads to more amorphous structure, thereby increasing diffusion and permeability of gases. [Emim][BF4] was added to the polymer solution up to 100wt% of Pebax1657 weight and permeation coefficients of CO2, H2, CH4 and N2 through the prepared membranes were measured. The results showed remarkable increment in permeation of all the tested gases, particularly CO2 and ideal selectivity of CO2/H2 enhanced significantly due to high solubility selectivity of the added compound. Effect of operating conditions on solubility coefficients was also investigated; thus sorption isotherms and activation energies of permeability, solubility and diffusion were calculated. In addition, the membranes were characterized by SEM, DSC, FT-IR spectroscopy and Tensile analysis to inspect changes in their physical and thermal properties, precisely.

Transport properties of sulfonated poly (styrene‐isobutylene‐styrene) membranes with counter‐ion substitution

AbstractIn this study, the transport properties of poly(styrene‐isobutylene‐styrene) (SIBS) were determined as a function of sulfonation level (0–94.9%) and counter‐ion substitution (Ba+2, Ca+2, Mg+2, Mn+2, Cu+2, K+1) for fuel cell applications. Increasing the sulfonation level improved the ion exchange capacity (IEC) of the membranes up a maximum (1.71 mequiv/g), suggesting a complex three‐dimensional network at high sulfonation levels. Results show that proton conductivity increases with IEC and is very sensitive to hydration levels. Methanol permeability, although also sensitive to IEC, shows a different behavior than proton conductivity, suggesting fundamental differences in their transport mechanism. The incorporation of counter‐ion substitution decreases both methanol and proton transport. Methanol permeability seems to be related to the size of the counter‐ion studied, while proton conductivity is more sensitive to water content, which is also reduced upon the incorporation of counter‐ions. To complement the studies, selectivity (i.e., proton conductivity/methanol permeability) of the studied membranes was determined and compared to Nafion® 117. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Miscibility and Transport Properties of Poly(lactide)/Phenoxy System

AbstractSummary: The addition of Phenoxy to Polylactide causes a decrease of the permeability coefficients proportional to the amount of Phenoxy, even in spite of the lack of miscibility between both polymers. The effect of a Poly(caprolactone‐b‐lactide) multiblock copolymer as a compatibilizer of a Poly(lactide)/Phenoxy blend was analyzed,1 achieving miscibility and providing an improvement in the barrier properties of the blend.

Current Conduction in Poly(3-Hexylthiophene) and in Poly(3- Hexylthiophene) doped [6,6]-Phenyl C61-Butyric Acid Methylester Composite Thin Film Devices

Transport properties of poly(3-hexylthiophene) (P3HT), and of its blend with [6,6]-phenyl C61- butyric acid methylester (PCBM), were studied by analysing temperature dependent current-voltage characteristics of spin cast thin films sandwiched between aluminium electrodes in a metal-insulator- metal (MIM) configuration. It was found that in Al/P3HT/Al devices, the current is limited by space charge that accumulates near the hole injecting electrode due to the poor bulk transport properties of P3HT. At low temperatures and high applied electric fields the current density obeys a power law of the form J _ Vm, characteristic of space charge limited current (SCLC) in the presence of exponentially distributed traps within the band gap. These traps are filled by charge that is injected by quantum mechanical tunnelling, which is adequately described by the Fowler-Nordheim (FN) theory. By calculating the majority charge carrier mobility in Al/P3HT/Al and Al/P3HT:PCBM/Al devices from the Ohmic, SCLC, and FN tunnelling fits at different temperatures, we have obtained that the charge carrier mobility in P3HT is two orders smaller than the electron mobility in the P3HT:PCBM blend at room temperature, but comparable at low temperatures. This information is important in determining the origin of open circuit voltage and short circuit current limit in solar cells that employ this blend as the active layer.

The thickness dependence of Matrimid films in water vapor permeation

Composite or asymmetric membranes with thin active layers are used in industrial spiral-wound and hollow fiber modules to maximize productivity. These thin active layers are more susceptible to plasticization and undergo physical aging more rapidly than thick films. In this work, the sorption and transport properties of poly(3,3′-4, 4′-benzophenone tetracarboxylic-dianhydride diaminophenylindane) (Matrimid® 5218) as membranes of thickness 1–58μm were studied with mixed gas/water vapor feed streams (CH4, CO2 and H2O) at 7.5bar and 35°C. The fractional free volume (FFV) of the films decreased significantly with decreasing film thickness for films below 10–15μm. Water vapor solubility was independent of thickness, but water permeability reduced by an order of magnitude as film thickness decreased. This loss in permeability was related to a decrease in the diffusion coefficient, which was in turn related to the loss of fractional free volume. The net effect of competitive sorption between water vapor and gas components and CO2 induced plasticization effect resulted in a reduction in both carbon dioxide and methane permeabilities and CO2/CH4 selectivities as vapor activity increased.

Macrochain configuration, stucture of free volume and transport properties of poly(1-trimethylsilyl-1-propyne) and poly(1-trimethylgermyl-1-propyne)

The relationship between poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(1-trimethylgermyl-1-propyne) (PTMGP) microstructure, gas permeability and structure of free volume is reported. n-Butane/methane mixed-gas permeation properties of PTMSP and PTMGP membranes with different cis-/trans-composition have been investigated. The n-butane/methane selectivities for mixed gas are by an order higher than the selectivities calculated from pure gas measurements (the mixed-gas n-butane/methane selectivities are 20–40 for PTMSP and 22–35 for PTMGP). Gas permeability and n-butane/methane selectivity essentially differ in polymers with different cis-/trans-composition. Positron annihilation lifetime spectroscopy investigation of PTMSP and PTMGP with different microstructure has determined distinctions in total amount and structure of free volume, i.e. distribution of free volume elements. The correlation between total amount of free volume and gas transport parameters is established: PTMSP and PTMGP with bigger free volume exhibit higher n-butane permeability and mixed-gas n-butane/methane selectivity. Such behavior is discussed in relation to the submolecular structure of polymers with different microstructure and sorption of n-butane in polymers with different free volume.

Molecular simulation on the transport properties of poly[1-trimethylsilyl-1-propyne] for organic-vapor/permanent-gas separation

Molecular dynamics simulation and Grand canonical Monte Carlo (GCMC) simulation are used to investigate the performance of Poly [1-trimethylsilyl-1-propyne] (PTMSP) membrane for organic-vapor/permanent-gas separation. In general, the calculated diffusion and solubility coefficients of permanent gases and organic vapors in PTMSP are consistent with the experimental data, and correlate well with the square of the effective molecule diameter and critical temperature of each penetrant molecule. The simulation results reveal that the high organic-vapor/permanent-gas permeability selectivity of PTMSP can be attributed to the high organic-vapor/permanent-gas solubility selectivity. A comprehensive microscopic interpretation is provided based on the analysis of the center-of-mass displacements of penetrant molecules and the study of the free-volume size and distribution in PTMSP.

Fabrication and transport properties of poly(N-vinylcarbazole)-cellulose triacetate Langmuir-Schaefer films

Cellulose triacetate (CTA) was doped with poly(N-vinylcarbazole) during the oxidative polymerization of N-vinylcarbazole using ferric chloride as an initiator to form polymer blends. The blends were characterized by Fourier transform infrared and UV-vis spectroscopy. The surface morphology was further studied using both scanning electron microscopy and transmission electron microscopy. Langmuir-Schaefer films of the polymer blends were fabricated. The DC conductivity of the polymer films at room temperature was found to increase with an increase in CTA content up to a value of 0.001 S cm ―1 . The temperature-dependent DC conductivity of the polymer films studied in the range of 300-500 K shows an increase in conductivity with an increase in temperature indicating a semiconducting behavior with a negative temperature coefficient of resistivity. The apparent activation energy also showed a pronounced effect with an increase in the temperature as well as an increase in the content of CTA. POLYM. COMPOS., 32:79-88, 2011. © 2010 Society of Plastics Engineers.

The effect of acid-base interaction on the thermal and transport properties of poly(etheretherketone) based composite membranes

Binary composite membranes were prepared by the solution casting method from sulfonated poly(etheretherketone) (SPEEK) and organic additives such as hydroxyquinolinesulfonicacid (HQS), 4-tertiary butylpyridine (TBP), imidazole and succinimide. Ternary composite membranes were prepared from SPEEK, inorganic phosphotungstic acid (PWA) and the same organic additives. The acid base interaction characteristics of the composite membranes were not observed by ATR-FTIR analysis. TGA results showed that the thermal stability of the composite membranes was enhanced in the temperature range up to about 400 °C by the addition of the organic additives. The acid-base interaction between SPEEK and the organic additives of HQS, TBP and imidazole decreased the water uptake, methanol permeability and proton conductivity of the binary and ternary composite membranes. However, the addition of succinimide did not decrease the water uptake, proton conductivity and methanol permeability of the composite membranes. The composite membranes containing succinimide made little acid-base interaction but made hydrogen bonding with SPEEK. The hydrogen bonding proved to be weaker than the acid-base interaction. The selectivity of the composite membranes increased by the addition of PWA, and the selectivities of the composite membranes containing succinimide were higher than those of the other composite membranes.

Properties of poly(ethylene terephthalate) track membranes with a polymer layer obtained by plasma polymerization of pyrrole vapors

The structure and the charge transport properties of poly(ethylene terephthalate) track membrane modified by pyrrole plasma were studied. It was found that polymer deposition on the surface of a track membrane via plasma polymerization of pyrrole results in the creation of composite nanomembranes that, in the case of the formation of a semipermeable layer, possess asymmetric conductivity in electrolyte solutions – a rectification effect similar to that of a p–n junction in semiconductors. It is caused by presence in the membranes of two layers with different functional groups and also by the pore geometry. Such membranes can be used to create chemical and biochemical sensors.

Transport properties of poly(GACT)-poly(CTGA) deoxyribonucleic acid: A ladder model approach

In this paper, based on the tight-binding Hamiltonian model and within the framework of a generalized Green’s function technique, the electronic conduction through the poly(GACT)-poly(CTGA) DNA molecule in SWNT/DNA/SWNT structure has been numerically investigated. In a ladder model, we consider DNA as a planar molecule containing M cells and four further sites (two base pair sites and two backbone sites) in each cell, sandwiched between two semi-infinite single-walled carbon nanotubes (SWNT) as the electrodes. Having relied on Landauer formalism, we focussed on studying the current-voltage characteristics of DNA, the effect of the coupling strength of SWNT/DNA interface and the role of tube radius of nanotube contacts on the electronic transmission through the foregoing structure. Finally, a characteristic time was calculated for the electron transmission, which measures the delay caused by the tunnelling through the SWNT/DNA interface. The results clearly show that the calculated characteristic time and also the conductance of the system are sensitive to the coupling strength between DNA molecule and nanotube contacts.