Arrhenius Temperature Dependence Research Articles

Investigation of cyclopentene + OH and cyclopentene thermal decomposition reactions

This study presents the first high-temperature measurements of cyclopentene+OH→k1Products reaction over 856 – 1258 K and 1.03 – 4.33 bar. The determined rate coefficients of k1 exhibited Arrhenius temperature dependence with an activation energy ∼ 3.3 kcal mol−1 and negligible pressure dependence. Rate coefficients of OH + cyclopentene are faster than OH + 1-pentene but comparable to OH + 2-pentene, highlighting the significance of allylic CH bonds in these reactions. At 1258 K, our rate coefficient is ∼ 30 % slower than the average room-temperature measurement, indicating the role of OH-addition pathways at low temperatures. Site-specific rate coefficients and branching ratios are determined, with H-abstraction at the allylic CH site accounting for ∼68 % of the reaction and alkylic CH bond contributing ∼22 %. Our measured k1 may be given as (unit: cm3molecule−1s−1):k1=1.64×10−10e(−1660T)Cyclopentene decomposition reaction (cyclopentene→k2cyclopentadiene+H2) is studied over 1186–1472 K and 1.17 – 1.38 bar. Time-resolved yields of the product, cyclopentadiene, are monitored using a sensitive UV laser diagnostic near 220 nm. Absorption cross-sections of cyclopentadiene, measured in two separate mixtures, showed weak positive temperature dependence (8.7 – 9.8 × 10−18 cm2molecule−1) over 961 – 1326 K. Our rate coefficients of k2 exhibited a positive Arrhenius temperature dependence with an activation energy of ∼ 54.7 kcal mol−1. At 1300 K, the decomposition of cyclopentene proceeds 5.5 and 28 times faster than that of cyclopentadiene and cyclopentane, respectively. Our measured k2 may be expressed as (unit: s−1):k2=2.55×1012e(−27,527.6T)The pentagonal structure of cyclopentene influences its H-abstraction and decomposition reactions distinctively. While H-abstraction by OH follows a mechanism akin to cyclohexene and linear alkenes, with comparable rate coefficients at allylic CH bonds, the penta-ring structure significantly impacts the decomposition mechanism. Cyclopentene decomposition predominantly produces cyclopentadiene and H2 in a ring-conserving manner, differing from the cleavage of allylic-alkylic CC bonds in the decompositions of 1-alkenes and cyclohexene.

Electron Transport in a Fluorine-Based Copolymer: Evidence for the Absence of Correlated Disorder

Spatial correlation between two unordered transmission site energies of semiconducting polymers applied to organic electronic devices can impact the charge carrier mobility (CCM). It has been uncertain if this spatial correlation exists in relevant polymers. This study focuses on electronic transmission in a fluorene-based copolymer called poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)](F8BT) commonly applied to polymer light-emitting diodes (PLEDs). In terms of the F8BT-based electron-only device (EOD), the layer thickness dependence (Ltd.) of the current density is analyzed. Two models are adopted, with the intention of depicting the electronic transmission: the improved extended Gaussian disorder model(IEGDM) and extended correlated disorder model (ECDM). The IEGDM considers the dependence of the CCM upon electric field, temperature, and carrier density, incorporating the influences of Arrhenius and non-Arrhenius temperature dependence. In addition, the ECDM includes or excludes the spatial correlations between two site energies. Current-voltage J – V features are analyzed using IEGDM and ECDM. The two models provide eminent fits. A contrast between the parameters of the models reveals a more practical intersite distance by IEGDM (1.3 nm) than the value by ECDM (0.4 nm). This suggests that correlations between the site energies may not be significant or may be absent. Therefore, through the analysis, the evidence is provided for the absence of correlated disorders.

Ultralow-Friction at Cryogenic Temperature Induced by Hydrogen Correlated Quantum Effect.

Temperature is one of the governing factors affecting friction of solids. Undesired high friction state has been generally reported at cryogenic temperatures due to the prohibition of thermally activated processes, following conventional Arrhenius equation. This has brought huge difficulties to lubrication at extremely low temperatures in industry. Here, the study uncovers a hydrogen-correlated sub-Arrhenius friction behavior in hydrogenated amorphous carbon (a-C:H) film at cryogenic temperatures, and a stable ultralow-friction over a wide temperature range (103-348 K) is achieved. This is attributed to hydrogen-transfer-induced mild structural ordering transformation, confirmed by machine-learning-based molecular dynamics simulations. The anomalous sub-Arrhenius temperature dependence of structural ordering transformation rate is well-described by a quantum mechanical tunneling (QMT) modified Arrhenius model, which is correlated with quantum delocalization of hydrogen in tribochemical reactions. This work reveals a hydrogen-correlated friction mechanism overcoming the Arrhenius temperature dependence and provides a new pathway for achieving ultralow friction under cryogenic conditions.

Activation energy and molecular weight dependence of cooperative tracer chains diffusion in highly entangled polymer melts

AbstractThe generalized Langevin equation for cooperative dynamics of Guenza predicts the dynamics of chains in entangled polymers is cooperative with anomalous properties, and at variance with the tube‐reptation model. The center‐of‐mass mean‐square displacements at shorter times are subdiffusive with with β < 1, contradicting the common assumption of reptation within the tube. At some longer time the subdiffusive dynamics exhibits the crossover to free diffusion with . Moreover the subdiffusive dynamics is heterogeneous, non‐Gaussian, and cooperative. These predictions have been confirmed by using neutron spin echo spectroscopy in entangled polyethylene melts [M. Zamponi, et al. J. Phys. Chem. B 2008, 112, 16220], and in tracer diffusion of short polyethylene chains in a highly entangled polyethylene melt [M. Zamponi et al. Phys. Rev. Lett. 2021, 126, 187801]. The latter was confirmed in poly(ethylene oxide) tracer diffusion in highly entangled poly(ethylene oxide) melt [M. Kruteva et al. Macromolecules 2021, 54, 11384]. Notwithstanding, there are other important data sets obtained in the NSE experiments but were left unexplained. One set consists of the activation energies of the Arrhenius temperature dependence of D for each tracer. Another is the molecular weight dependence of D of the tracers determined at the same temperature. In this article the predictions of the Coupling Model are applied to these two sets of data. Good quantitative agreements of the CM predictions with experimental data provide additional support to the cooperativity dynamics of entangled polymers as concluded by others. Additionally, all the properties of cooperative diffusion of entangled polymer chains are shown to be isomorphic to those found in cooperative diffusions in totally different systems. Diffusion in all are governed by interaction between the diffusing units, and from which the universal properties originate.

Arrhenius temperature dependence of the crystallization time of deeply supercooled liquids

Arrhenius temperature dependence of the crystallization time of deeply supercooled liquids

Allylic-alkylic C-C bond decomposition in 1-butene and 1-pentene

1-Butene and 1-pentene are critical intermediates in the oxidation and pyrolysis of larger alkanes and alcohols. Their thermal decomposition plays important role in fuel consumption under combustion conditions, yet seldom investigated. In this work, we studied the title reactions behind reflected shock waves over temperatures of 1178 – 1416 K and pressures near 1.2 bar. We monitored absorbance time-history of the product allyl radicals by employing a sensitive UV diagnostic scheme at a wavelength of 220 nm. We extracted the target rate coefficients by simulating the measured absorbance profiles with detailed kinetic models. Our determined rate coefficients of 1-butene (k1) and 1-pentene (k2) thermal decomposition may be expressed as (unit s−1):k1(1C4H8→CH3+aC3H5)=1.52×1016e(−37937T)k2(1C5H10→C2H5+aC3H5)=3.84×1014e(−31434T)We believe the current work provides the first direct measurements of these reactions. Our 1-butene thermal decomposition rate coefficients exhibit a positive Arrhenius temperature dependence. Around 1350 K and 1 bar, 1-butene decomposition proceeds ∼ 4.5 times faster than n-butane, and ∼ 66 times faster than 1,3-butadiene. Our work extends the literature measurements of 1-butene decomposition to temperatures higher than 1310 K. Literature measurements above 1000 K underestimate our rate coefficients by ∼ 20 %. Additionally, our 1-butene rate coefficients provide an analogy to bio-derived molecules containing similar allylic-alkylic C-C bonds, such as methyl-3-hexenoate. For 1-pentene thermal decomposition, we observed the product allyl radicals starting from 1178 K compared to 1213 K in 1-butene measurements. Thus 1-pentene decomposition proceeds 2 – 6 times faster than 1-butene, and shows a gentler Arrhenius temperature dependence. The current literature models exhibit a range of rate values that vary by an order of magnitude, resulting in noticeable discrepancies. Our study addresses this issue by providing much-needed clarity and precision. Furthermore, we implemented our rate coefficients in literature kinetic models and evaluated their influence on ignition delay time (IDT) and speciation measurements. The results indicate that our rate coefficients generally improved the model performance.

Solute influence in transitions from non-Arrhenius to stick-slip Arrhenius grain boundary migration

Synthetic driving force based molecular dynamics simulations are used to evaluate the grain boundary velocities for an incoherent Σ3 [111] 60° {11 8 5} GB in elemental nickel and its copper-based alloys in the dilute limit. We examine the effects of temperature, solute content, and magnitude of the driving force on grain boundary velocity trends and their associated mechanisms. We observe that, for pure nickel and its copper alloys in the dilute limit at high driving forces, these special grain boundaries exhibit non-Arrhenius or anti-thermal migration behavior, where temperature and grain boundary velocity are inversely related. For lower driving forces, the increased copper content leads to stick-slip migration behavior and a likely transition from non-Arrhenius to Arrhenius temperature dependence. Interestingly, the ordered atomic motions are frustrated but unchanged by the solute content and stick-slip migration. While the results are generally consistent with the Cahn-Lücke-Stüwe (CLS) model, no solute drag is observed; rather, the solute effects are likely the result of solute pinning.

A framework for modeling of catalyst deactivation and coking free of main-reaction kinetics in methanol to gasoline process

Optimizing the methanol-to-gasoline technology necessitates a profound comprehension of catalyst deactivation and coke formation kinetics. However, conventional mathematical models cannot capture catalyst deactivation without relying on complex main-reaction kinetic models, and they treat the prediction of coking as a separate problem. Addressing these challenges, this research introduces a computational framework to identify the optimal model for the kinetics of deactivation and coking. The key novelty is leveraging the concept of active site loss to eliminate the requirement for main-reaction kinetic models while facilitating the prediction of coking according to the site loss model. Experimental data of an HZSM-5 catalytic bed under diverse operating conditions (WHSV: 10–100 h−1, temperature: 325–375 °C) were employed to validate method efficiency for predicting reactor outputs, including oxygenates, light olefins, and gasoline. The proposed approach demonstrates a 0.52 % Root-Mean-Square-Error in simulating product weights and a 66 % reduction in deactivation kinetic constants. This study reveals assuming a critical volume for each grown coke precursor justifies experimental data by R2 of 99.71 %. This volume was computed around 100 Å3 and exhibits a linear Arrhenius temperature dependency. These results highlight the high accuracy and extreme simplicity this framework offers. Moreover, the method transforms deactivated catalyst data at varying WHSVs into a larger unified dataset for the fresh catalyst at each isotherm. Hence, it also positively impacts the kinetic study of main reactions. Consequently, the developed framework is a promising tool for direct assessment of catalyst deactivation and coking in similar processes toward advancing catalyst design strategies and fuel production efficiency.

The relaxation dynamics and dielectric properties of cyanobiphenyl-based nematic tripod liquid crystals

We present a detailed investigation of the phase behaviour, molecular relaxation dynamics, rheology and dielectric properties of two cyanobiphenyl-based liquid crystal (LC) tripods, differing only in the length of their spacer units (6 or 9 carbons). These LC tripods combine properties of low molecular weight LCs and LC polymers, resulting in a range of advantageous properties including a wide nematic range (ΔT>90 K) and a large birefringence (0.3 at T−TNI=-80 K for the 6 spacer tripod). Using broadband dielectric relaxation spectroscopy, calorimetry, oscillatory and steady state shear rheology, we identified four molecular relaxation processes: the structural (α) relaxation (defining the glass transition temperature, Tg); the δ relaxation (reorientation of the mesogen unit around its short axis); the β relaxation (reorientation around its long axis); and the γ relaxation (internal tripod arm fluctuations). The β and γ relaxations follow Arrhenius temperature dependencies in the glass, whereas the α and δ relaxations merge above, but near Tg, where they follow a non-Arrhenius VFT behaviour. For higher temperatures, the two relaxations separate and for T>T⁎, where T⁎ marks a dynamic crossover, the α relaxation transitions from VFT to Arrhenius behaviour. For the two tripods, ratios of T⁎/Tg=1.14 and T⁎/Tg=1.13 were observed respectively, consistent with the ratio observed for many side-chain LC polymers (and other LC systems), and consistent with the ratio where a dynamic crossover is typically observed also for non-LC glass-formers. However, for non-LC systems, the transition to Arrhenius behaviour happens at significantly higher temperatures relative to Tg and the dynamic crossover at T⁎ is typically observed as a transition between two different VFT behaviours. We argue that for the tripods these differences arise from differences in the molecular relaxation mechanisms induced by the LC order. Finally, for temperatures where δ and α relaxations are separated, we find that ion conductivity decouples from the α relaxation, instead following the δ relaxation; this demonstrates that the ion transport properties for the tripods can be tuned by the design of the tripod mesogen arm.

The effect of a temperature-dependent viscosity on cooling droplet-droplet collisions

A detailed understanding of the collision dynamics of liquid droplets is relevant to natural phenomena and industrial applications. These droplets could experience temperature changes altering their physical properties, which affect the droplet collisions. As viscosity is one of the relevant physical properties, this study focuses on the effect of temperature on viscosity, with an Arrhenius temperature dependence, of collisions of two equal-sized droplets using the Volume of Fluid Method. The results show that the higher temperature of the droplets leads to an effectively lower viscosity, leading to increased interface oscillations. This leads to the onset of separation at lower Weber numbers as expected. The local cooling droplets will create a local viscosity profiles, which results in the formation of a ridge upon combination of droplets. In addition, the collision outcomes sometimes cannot be explained solely on basis of an effective viscosity, undermining the usefulness of existing collision regime maps.

Efficacy of an off-line constructed wetland for mitigating nitrogen loss from a pastoral catchment

ABSTRACT Constructed wetlands are an established mitigation option for reducing contaminant loads from pastoral land in New Zealand. We assess the long-term performance of a 0.5 ha, off-line, horizontal surface flow wetland, installed on a dairy farm with the primary objective of nitrate removal. Over seven years the median removal rates for nitrate-nitrogen (NO3–N), total nitrogen and total suspended solids were 45%, 33% and 74%, respectively. Whilst dissolved reactive phosphorus (DRP) was initially removed, over time the wetland progressed to a small exporter of DRP. Median NO3–N mass removal was 417 kg yr−1 , which is considerable for such a small wetland, and equivalent to 7% of total modelled ‘farm-scale’ losses. Nitrate removal was found to be seasonal and although it could be simulated using a conventional wetland model with Arrhenius temperature dependence, the resulting joint estimates of k 20 and Θ were uncertain. We estimate the NO3–N removal cost-effectiveness of the wetland (over a 25-year lifespan) to be NZ$34 kg N−1. We foresee opportunities for off-line constructed treatment wetlands to be an effective nitrate mitigation option in perennial drains and lowland streams in pastoral catchments, but also emphasise the need for on-going maintenance to ensure longevity of performance.

Predicted viscosity of liquid HMX up to 40 GPa

AbstractViscous flow serves as a significant heating mechanism during the formation of hot spots, but the shear viscosity which determines this response is poorly characterized for most high explosives. Recently, a model was proposed for the shear viscosity of liquid HMX (1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane) that was fit to pressures reaching 5 GPa, but this work uncovered uncertainties in the viscosity at 0 GPa and remains untested at higher pressures. We use molecular dynamics (MD) simulations and the Green‐Kubo formalism to predict the temperature‐ and pressure‐dependent shear viscosity of HMX over the pressure interval 0 GPa≤P≤40 GPa. Reassessment of the viscosity at 0 GPa rules out several potential explanations for discrepancies between earlier reports; we attribute these differences to details of MD trajectory integration impacting molecular flexibility. The shear viscosity of HMX exhibits an Arrhenius temperature dependence at each pressure considered, with exponential prefactor and activation energy terms that are also strong functions of pressure. An analytic form for the viscosity is developed based on an extension of the well‐known Andrade equation that simultaneously captures the temperature and pressure dependencies in the MD data up to 40 GPa. Comparison against a recently developed model for the viscosity of liquid RDX (1,3,5‐trinitro‐1,3,5‐triazinane) shows that both materials exhibit similar functional dependencies with the viscosity of HMX being higher by roughly an order of magnitude at a given temperature‐pressure state.

Analytic models for organic field-effect transistors based on exponential and power mobility models

The fundamental I–V formula of an organic field effect transistor (OFET) is improved to overcome the divergence of the integrand, so it is very convenient for both numerical calculations and analytic derivations. The analytic I–V formulae are derived based on the exponential mobility model and power-function mobility model, respectively, and the derived analytic formulae are applied to three OFET devices. The results calculated from the reformulated analytic I–V formulae taking in exponential and power function mobility models are all in good agreement with the experimental I–V data. The parameters μ 0 and γ that are extracted from the mobility model and fitted by experimental data show simple Arrhenius temperature dependence and inverse linear relationship with temperature, respectively. These findings are very useful for practical applications and device simulations.

Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins.

Hydrated proteins undergo a transition in the deeply supercooled regime, which is attributed to rapid changes in hydration water and protein structural dynamics. Here, we investigate the nanoscale stress-relaxation in hydrated lysozyme proteins stimulated and probed by X-ray Photon Correlation Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamics in the deeply supercooled regime (T = 180 K), which is typically not accessible through equilibrium methods. The observed stimulated dynamic response is attributed to collective stress-relaxation as the system transitions from a jammed granular state to an elastically driven regime. The relaxation time constants exhibit Arrhenius temperature dependence upon cooling with a minimum in the Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is attributed to an increase in dynamical heterogeneity, which coincides with enhanced fluctuations observed in the two-time correlation functions and a maximum in the dynamic susceptibility quantified by the normalized variance χT. The amplification of fluctuations is consistent with previous studies of hydrated proteins, which indicate the key role of density and enthalpy fluctuations in hydration water. Our study provides new insights into X-ray stimulated stress-relaxation and the underlying mechanisms behind spatiotemporal fluctuations in biological granular materials.

Development of a new approach for the kinetic modeling of the lithium reactive hydride composite (Li-RHC) for hydrogen storage under desorption conditions

Among some promising candidates for high-capacity energy and hydrogen storage is the Lithium-Boron Reactive Hydride Composite System (Li-RHC: 2 LiH + MgB2/2 LiBH4 + MgH2). This system desorbs hydrogen only at relatively high temperatures and presents a two-step series of reactions occurring in different time scales: first, MgH2 desorbs, followed by LiBH4. Hitherto, the dehydrogenation kinetic behavior of such a system has been described for different temperatures at specific values of operative pressure. However, a comprehensive model representing its dehydrogenation kinetic behavior under different operative conditions has not yet been developed. Herein, the separable variable method is applied to develop a comprehensive kinetic model, including the two-step dehydrogenation series reaction. The MgH2 decomposition is described with the one-dimensional interface-controlled reaction rate Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) with a (Pequilibrium/Poperative) pressure functionality and an Arrhenius temperature dependence activation energy of 63 ± 3 kJ/mol H2. The LiBH4 decomposition is modeled applying the autocatalytic Prout-Tompkins model. A novel approach to describe the Prout-Tompkins t0 parameter as a function of the operative temperature and pressure model is proposed. This second reaction step presented a (Pequilibrium – Poperative/Pequilibrium)2 pressure dependence and an Arrhenius temperature dependence with activation energy 94 ± 13 kJ/mol H2. The proposed approach is experimentally and computationally validated, successfully describing the decomposition kinetic behavior of MgH2 and LiBH4 under three-phase gas, liquid and solid environment and shows good agreement between experimental and modeled curves.

Molecular Mechanism of the Debye Relaxation in Monohydroxy Alcohols Revealed from Rheo-Dielectric Spectroscopy.

Rheo-dielectric spectroscopy is employed to investigate the effect of external shear on Debye-like relaxation of a model monohydroxy alcohol, i.e., the 2-ethyl-1-hexanol (2E1H). Shear deformation leads to strong acceleration in the structural relaxation, the Debye relaxation, and the terminal relaxation of 2E1H. Moreover, the shear-induced reduction in structural relaxation time, τ_{α}, scales quadratically with that of Debye time, τ_{D}, and the terminal flow time, τ_{f}, suggesting a relationship of τ_{D}^{2}∼τ_{α}. Further analyses reveal τ_{D}^{2}/τ_{α} of 2E1H follows Arrhenius temperature dependence that applies remarkably well to many other monohydroxy alcohols with different molecular sizes, architectures, and alcohol types. These results cannot be understood by the prevailing transient chain model, and suggest a H-bonding breakage facilitated sub-supramolecular reorientation as the origin of Debye relaxation of monohydroxy alcohols, akin to the molecular mechanism for the terminal relaxation of unentangled "living" polymers.

Physical Aging Behavior of the Side Chain of a Conjugated Polymer PBTTT

This paper provides a viewpoint of the technology of the fast-scanning calorimetry with the relaxation behavior of disordered side chains of poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C12) around the glass transition temperature of the side chains (Tg,γ). PBTTT is an ideal model of the high-performance copolymer of poly(alkylthiophenes) with side chains. The γ1 relaxation process of the disordered side chains of PBTTT was detected as a small endothermic peak that emerges before the γ2 relaxation process. It shows an increase with increasing temperature as it approaches the glass transition temperature of the disordered side chains of PBTTT. The ductile-brittle transition of PBTTT in low temperatures originating from the thermal relaxation process is probed and illustrated by physical aging experiments. The signature is shown that the relaxation process of the disordered side chain of PBTTT at low temperatures varies from Arrhenius temperature dependence to super Arrhenius temperature dependence at high temperatures. These observations could have significant consequences for the stability of devices based on conjugated polymers, especially those utilized for stretchable or flexible applications, or those demanding mechanical robustness during tensile fabrication or use in a low-temperature environment.

Application of amber suppression to study the role of Tyr M210 in electron transfer in R. sphaeroides photosynthetic reaction centers.

The bacterial photosynthetic reaction center (RC) is an important system to understand the structure and chemistry of the biological process of photosynthesis. In wild type reaction centers and at room temperature, the unidirectional electron transfer from the excited-primary donor P∗ to the A-side bacteriopheophytin HA takes place via a two-step mechanism, where P∗ transfers an electron to the A-side bacteriochlorphyll BA in 3 ps making P+BA-, which then transfers an electron in 1 ps to HA to make P+HA-. Even though RCs have a pseudo-C2 symmetry, electron transfer only occurs along the A-branch. Tyrosine M210 has been a key amino acid of particular interest since it is a clear deviation in symmetry between the two sides of RC, and many mutations have been made at this site. One interesting finding was that when M210 is mutated to phenylalanine, the electron transfer from P∗ and HA slows down from ∼4 ps to ∼11 ps and becomes temperature independent (Nagarajan et al. 1990, PNAS). By using amber suppression, we were able to incorporate phenylalanine variants with different electron-withdrawing/donating capabilities at position M210. To our surprise, transient absorption data shows that YM210F RCs do not exhibit temperature independent primary charge separation. In fact, YM210F RCs and all M210 phenylalanine variants RCs exhibit Arrhenius temperature dependence in contrast to WT, wherein the rate increases at low temperature. Significantly, the 1020 nm band, which is characteristic of P+BA-, was not observed at any time for any of the M210 phenylalanine variants RCs nor YM210F RCs, indicating a change to the one-step superexchange mechanism for electron transfer.

Molecular dynamics and conduction mechanism of poly(vinyl chloride‐co‐vinyl acetate‐co‐2‐hydroxypropyl acrylate) terpolymer containing ionic liquid

AbstractDielectric spectroscopy (DS) measurements were performed to probe the segmental dynamics and ion mobility of poly(vinyl chloride‐co‐vinyl acetate‐co‐2‐hydroxypropyl acrylate) terpolymer dopped with different amounts of tetrabutylammonium tetrafluoroborate ([TBA] [BF4]) ionic liquid (IL). Differential scanning calorimetry (DSC) was also employed to trace the change in the glass transition temperature (Tg) at different loads of IL. The DSC measurements revealed a remarkable reduction in the PVVH Tg from 344 to 310 K just by adding 20 wt% of IL. The DS measurements revealed three relaxation processes named α, β1, and β2. The α‐process is related to the segmental motion of PVVH while the β1 and β2 are due to the restricted local dynamics of side chains. The segmental relaxation times (α‐relaxation) speed up with increasing the concentration of IL due to the plasticization effect of IL on polymer chains. The temperature dependence of α‐relaxation follows the Vogel‐Fulcher‐Tammann (VFT) relation with dynamic glass transition between 323 and 294 K in agreement with the DSC measurements. The β1 and β2‐relaxations have an Arrhenius temperature dependence. The temperature dependence of ionic conductivity obeys the VFT behavior indicating the coupling between the segmental motion of PVVH chains and ion transport. Polaronic tunneling is the predominant conduction mechanism in PVVH and its composites. The specific capacitance increases with increasing both the temperature and IL concentration.

Effects of Ni dopant on morphology, crystal and electronic structure, electrical properties of sodium trititanate

Sodium trititanate doped with nickel in different amounts for the first time have been prepared through one-step hydrothermal synthesis. Both cation substitution and interstitial doping are realized with a formation of oxygen-deficient Na2+xTi3–yNix+yO7–δ solid solutions. The Ni-doping results in the sodium trititanate unit cell expansion. The morphology was found to be evolved with increasing dopant concentration from nanotubes to nanosheets. The specific surface area ranges from 121 to 78 m2 g–1 depending on dopant content. With nickel-doping, the bandgap narrowed from 3.45 up to 2.94eV. The conductivity of sodium trititanate increases in 3–6 fold after the nickel incorporation. A deviation from the Arrhenius temperature dependence of the conductivity is observed above 350 K indicating that mixed ionic-electronic conductors based on Ni-doped sodium trititanate are formed. This paper contributes to the advance understanding doping principles and effects for Na2Ti3O7-based materials, which are currently under consideration.