non-Arrhenius Dependence Research Articles

Modulating Phase Behavior in Fatty Acid-Modified Elastin-like Polypeptides (FAMEs): Insights into the Impact of Lipid Length on Thermodynamics and Kinetics of Phase Separation.

Although post-translational lipidation is prevalent in eukaryotes, its impact on the liquid-liquid phase separation of disordered proteins is still poorly understood. Here, we examined the thermodynamic phase boundaries and kinetics of aqueous two-phase system (ATPS) formation for a library of elastin-like polypeptides modified with saturated fatty acids of different chain lengths. By systematically altering the physicochemical properties of the attached lipids, we were able to correlate the molecular properties of lipids to changes in the thermodynamic phase boundaries and the kinetic stability of droplets formed by these proteins. We discovered that increasing the chain length lowers the phase separation temperature in a sigmoidal manner due to alterations in the unfavorable interactions between protein and water and changes in the entropy of phase separation. Our kinetic studies unveiled remarkable sensitivity to lipid length, which we propose is due to the temperature-dependent interactions between lipids and the protein. Strikingly, we found that the addition of just a single methylene group is sufficient to allow tuning of these interactions as a function of temperature, with proteins modified with C7-C9 lipids exhibiting non-Arrhenius dependence in their phase separation, a behavior that is absent for both shorter and longer fatty acids. This work advances our theoretical understanding of protein-lipid interactions and opens avenues for the rational design of lipidated proteins in biomedical paradigms, where precise control over the phase separation is pivotal.

Entropy scaling laws in self propelled glass formers

Predicting transport from equilibrium structure is a challenging problem in liquid state physics. Here we probe a glass forming liquid composed of self-propelled “active” particles and show that increasing the duration of self-propulsion makes the pair excess entropy negatively larger. The associated reduction in the number of accessible configurations per particle leads to a reduction in self-diffusivity. At moderate supercooling, the self-diffusivity is Arrhenius and in a reduced form obeys a Dzugutov like scaling law, directly yielding us a pair excess entropy that is inversely proportional to the effective temperature. In the strongly super-cooled regime, Dzugutov law does not apply and we observe that, the pair excess entropy shows a non-Arrhenius (power law) dependence on the effective temperature with an exponent that depends on the self propulsion time of the active particles. To demonstrate the generality of our scaling laws in moderately high temperatures, we set the particle interactions to be purely repulsive in one case and Lennard-Jones in the other, and find that in both the cases, the reported high temperature scaling laws are robust over variations in the duration of self propulsion. Our results may apply to transport in active colloidal suspensions, passive tracers in bacterial baths, and self-propelled granular media, to mention a few.

Introducing effective temperature into Arrhenius equation with Meyer-Neldel rule for describing both Arrhenius and non-Arrhenius dependent drain current of amorphous InGaZnO TFTs

The drain current of the amorphous InGaZnO thin-film transistors (TFTs) shows the Arrhenius and the non-Arrhenius dependence at the high temperature and the low temperature respectively. The gate-voltage-dependent effective temperature is introduced into the Arrhenius equation. Considering the normal Meyer-Neldel (MN) rule and the inverse MN rule, the equation successfully describes both the Arrhenius and the non-Arrhenius dependent drain current at the low and the high gate voltage. The calculated results of the equation are verified by the available experimental data of the amorphous La-doped InZnO TFT and the amorphous InGaZnO (InO3:Ga2O3:ZnO = 1:1:1 mol%) TFT.

Primary α and secondary β relaxation dynamics of meta-toluidine in the liquid state investigated by broadband dielectric spectroscopy.

We report a broadband dielectric spectroscopic (BDS) study on the clustering fragile glass-former meta-toluidine (m-TOL) from 187 K up to 289 K over a wide frequency range of 10-3-109 Hz with focus on the primary α relaxation and the secondary β relaxation above the glass temperature Tg. The broadband dielectric spectra were fitted by using the Havriliak-Negami (HN) and Cole-Cole (CC) models. The β process disappearing at Tβ,disap = 1.12Tg exhibits non-Arrhenius dependence fitted by the Vogel-Fulcher-Tamman-Hesse equation with T0βVFTH in accord with the characteristic differential scanning calorimetry (DSC) limiting temperature of the glassy state. The essential feature of the α process consists in the distinct changes of its spectral shape parameter βHN marked by the characteristic BDS temperatures TB1βHN and TB2βHN. The primary α relaxation times were fitted over the entire temperature and frequency range by several current three-parameter up to six-parameter dynamic models. This analysis reveals that the crossover temperatures of the idealized mode coupling theory model (TcMCT), the extended free volume model (T0EFV), and the two-order parameter (TOP) model (Tmc) are close to TB1βHN, which provides a consistent physical rationalization for the first change of the shape parameter. In addition, the other two characteristic TOP temperatures T0TOP and TA are coinciding with the thermodynamic Kauzmann temperature TK and the second change of the shape parameter at around TB2βHN, respectively. These can be related to the onset of the liquid-like domains in the glassy state or the disappearance of the solid-like domains in the normal liquid state.

Influence of Mo-doping on structure and oxygen permeation properties of SrCo0.8−xFe0.2MoxO3-δ perovskite membranes for oxygen separation

The effect of cobalt substitution by highly charged Mo6+ cations in SrCo0.8Fe0.2O3-δ (SCF) on the structure, microstructure, oxygen permeation performance and stability in the atmosphere containing carbon dioxide was systematically investigated by XRD, HT-XRD, Mossbauer spectroscopy, oxygen release technique and oxygen permeation experiments. The decrease in oxygen stoichiometry of SrCo0.8-xFe0.2MoxO3-δ (SCFM) materials was accompanied by nanostructuring with observed formation of nanosized domains with ordered oxygen vacancies. Equilibrium "3−δ−lg pO2−T" diagrams showed that SCF doping by molybdenum leads to broadening of the P1 (cubic perovskite phase) stability region. The obtained SCFM membrane materials possess improved phase stability in the intermediate temperature range (T < 700°C) and low oxygen partial pressure (pO2 < 0.06atm) compared to the undoped SCF oxide. The observed non-Arrhenius dependence of oxygen fluxes across SCFM disc membranes is related to combined control by bulk diffusion and surface exchange reactions.

Relaxor state and electric relaxations induced by the addition of Bi and Mn ions to Pb(Zr0.70Ti0.30)O3 ceramics

Abstract The (1 − x)Pb(Zr0.70Ti0.30)O3–xBiMn2O5 ceramics (PZT-BM), where x = 0, 0.02, 0.055, 0.11, 0.15, 0.22 and 1, were studied. We determined how addition of nonpolar BM influenced electrical properties of the ferroelectric PZT ceramics. Impedance spectroscopy measurements in broad frequency and temperature ranges were performed and several contributions to impedance response were identified. A crossover to the relaxor state was observed in the PZT-BM ceramics by doping with Bi and Mn ions. The relaxation times for the electric conductivity relaxation and dipole relaxation were estimated from electric modulus representation of the data. Activation energy values of the conductivity process, estimated for T > 510 K, decreased from 0.82 to 0.37 eV when BM content increased. The occurrence of the high-frequency dipole relaxation was assigned to the charge transfer of Ti3+/Ti4+, Zr3+/Zr4+ and Mn3+/Mn4+ ions. Occurrence of the ferroelectric relaxor features were deduced from the non-Arrhenius dependence of the relaxation times. Superposition of the relaxor features and electric relaxations provides high value permittivity (e′ > 1000) in wide temperature range (~ 250–573 K). This effect corresponds to the disorder and precipitation of ions that were shown using x-ray photoelectron spectroscopy and the time of flight–secondary ion mass spectrometry.

Crystallization Kinetics of GeSbTe Phase-Change Nanoparticles Resolved by Ultrafast Calorimetry.

Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime. Therefore, we present here an innovative exploration of the crystallization kinetics of Ge2Sb2Te5 (GST) nanoparticles (NPs) exploiting differential scanning calorimetry with ultrafast heating up to 40 000 K s–1. Our results demonstrate that the non-Arrhenius thermal dependence of viscosity at high temperature becomes an Arrhenius-like behavior when the glass transition is approached, indicating a fragile-to-strong (FS) crossover in the as-deposited amorphous GST NPs. The overall crystal growth rate of the GST NPs is unraveled as well. This unique feature of the FS crossover is favorable for memory applications as it is correlated to improved data retention. Furthermore, we show that methane incorporation during NP production enhances the stability of the amorphous NP phase (and thereby data retention), while a comparable maximum crystal growth rate is still observed. These results offer deep insight into the crystallization kinetics of nanostructured GST, paving the way for designing nonvolatile memories with PCM dimensions smaller than 20 nm.

From Entropic to Energetic: The Transformation Behavior of Potential Barriers

The diffusion of biased Brownian particles over an entropic barrier in a confined medium is investigated. By altering the direction of the external bias, the nature of the potential barriers changes from purely entropic to energetic. The strong non-Arrhenius dependence of the escape rate is observed due to a crossover between the entropy-dominated regime and energy-dominated regime under the cooperative effect of external bias and thermal motion.

A simple diatomic potential that prevents crystallization in supercooled liquids simulations

We study a simple and versatile diatomic potential function coined to prevent crystallization in supercooled liquids. We show that the corresponding liquid does not crystallize even with very long simulation runs at the lowest temperature that we can access with ergodic simulations. The medium displays the usual features of supercooled materials and a non-Arrhenius dependence of the diffusion coefficient and α relaxation time with temperature. We also observe the breakdown of the Stokes–Einstein relation at low temperatures.

Femtosecond and temperature-dependent picosecond dynamics of ultrafast excited-state proton transfer in water-dioxane mixtures.

Synthetic flavylium salts like the 7-hydroxy-4-methylflavylium (HMF) cation have been used as prototypes to study the chemistry and photochemistry of anthocyanins, the major group of water-soluble pigments in the plant kingdom. In this work, a combination of fluorescence upconversion with femtosecond time resolution and time-correlated single photon counting (TCSPC) with picosecond time resolution have been employed to investigate in details the excited-state proton transfer (ESPT) of HMF in water and in binary water/1,4-dioxane mixtures. TCSPC measurements as a function of temperature provide activation parameters for all of the individual rate constants involved in the proton transfer, including those for dissociation and recombination of the geminate excited base-proton pair (A*···H(+)) that can be detected in the water/dioxane mixtures (but not in water). Unlike the other rate constants, the deprotonation rate constant kd shows a non-Arrhenius dependence on temperature in both water and water/dioxane mixtures. At low temperatures kd is close to the dielectric relaxation rate of the solvent with a barrier of ca. 8 kJ mol(-1), suggesting that the solvent reorganization is the rate-limiting step. At higher temperatures (>30 °C) the proton transfer process is nearly barrierless and solvent-dependent. Fluorescence upconversion results in H2O, D2O, and water/dioxane mixtures confirm the two-step model for the ESPT of HMF and provide additional details of the early events prior to the onset of proton transfer, attributed to conformational relaxation and solvent reaccommodation around the initially formed excited state. The results are consistent with DFT calculations that indicate that charge redistribution occurs after rather than prior to the onset of the ESPT process.

Inorganic Electron Transfer: Sharpening a Fuzzy Border in Mixed Valency and Extending Mixed Valency across Supramolecular Systems

This article describes research from our laboratory on the chemistry and spectroscopic properties of inorganic mixed-valence complexes. After a brief review of the seminal work of Taube, Creutz, Day, Robin, Hush, and others in the 1960s and the confounding efforts to identify the borderline between class II and III mixed-valence systems in the 1990s and early 2000s, we describe our first experiments to observe and analyze the coalescence of ν(CO) band shapes in the 1D IR spectra of mixed-valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}(-), where L = a pyridyl ligand and BL = pyrazine or 4,4'-bipyridine, to estimate rate constants of intramolecular electron transfer (ET). The strong involvement of the bridging ligands in mixed-valence complexes of this type was first identified in the appearance of totally symmetric vibrational modes of pyrazine bridging ligands in the IR because of strong vibronic coupling within a three-state metal cluster-bridge-metal cluster model. Application of the Brunschwig-Creutz-Sutin semiclassical three-state model of mixed valency accounts well for the appearance of two intervalence charge-transfer bands that are observed in the near-IR region of the electronic absorption spectra of these mixed-valence ions. The direct spectroscopic observation of "mixed-valence isomers", the two alternate charge distributions of a mixed-valence ion, are described. The equilibrium constants of mixed-valence isomers provide quantitative thermodynamic estimates of the electronic coupling, H(ab). The extent of delocalization in many of the mixed-valent bridged dimers of triruthenium clusters produces unusual behavior, especially rate constants for ET that are independent of normal solvent reorganization energies but do depend on solvent dynamical dipolar reorientation times. The strong dependence of rates on solvent dynamics is also found to produce a non-Arrhenius dependence of ET rate constants on temperature, faster rates in frozen solutions compared to fluid solutions. The studies of these mixed-valence systems have provided generalized guidelines for establishing where a particular mixed-valence system lies along the class II/III delocalization transition, and they have increased our understanding of the ET dynamics at the delocalization threshold.

Diffusion over an entropic barrier: Non-Arrhenius behavior

We have examined the temperature dependence of noise-induced escape rate of brownian particles between two distinct regions in a two-dimensional enclosure through a narrow bottleneck. Varying cross section of the confinement results in an effective entropic barrier in reduced dimension. The strong non-Arrhenius dependence of the escape rate is observed, which can be explained in terms of a crossover between entropy-dominated regime and energy-dominated regime in presence of an interplay of gravitational bias and thermal motion.

Thermosensitive Water-Dispersible Hairy Particle-Supported Pd Nanoparticles for Catalysis of Hydrogenation in an Aqueous/Organic Biphasic System

We report in this article the use of thermosensitive water-dispersible polymer brush-grafted polymeric particles as carriers for Pd nanoparticles for the catalysis of hydrogenation of styrene in an aqueous/organic biphasic system. Thermoresponsive poly(methoxytri(ethylene glycol) methacrylate) brushes were grown from initiator-functionalized core-shell cross-linked poly( t-butyl acrylate) (P tBA) particles via surface-initiated atom-transfer radical polymerization. The t-butyl group of P tBA in the core was removed with trifluoroacetic acid, followed by loading of Pd2+ cations through ion exchange. Pd nanoparticles were prepared by reduction of Pd2+ ions with ethanol at 70 degrees C. Dynamic light scattering studies showed that the Pd nanoparticle-loaded thermosensitive hairy particles in water began to shrink when the temperature was above 30 degrees C. The supported Pd nanoparticles efficiently catalyzed hydrogenation of styrene in an aqueous/octane biphasic system and were reused five times with no changes in the yields in the first three cycles and slight decreases in the fourth and fifth cycles after the same period of time. Kinetics studies showed that the catalytic activity of Pd nanoparticles was modulated by the phase transition of the thermosensitive brush layer, resulting in a non-Arrhenius dependence of apparent initial rate constant, k app, on temperature.

Aqueous peptides as experimental models for hydration water dynamics near protein surfaces

We report quasi-elastic neutron scattering experiments to contrast the water dynamics as a function of temperature for hydrophilic and amphiphilic peptides under the same level of confinement, as models for understanding hydration dynamics near chemically heterogeneous protein surfaces. We find that the hydrophilic peptide shows only a single non-Arrhenius translational process with no evidence of spatial heterogeneity unlike the amphiphilic peptide solution that exhibits two translational relaxations with an Arrhenius and non-Arrhenius dependence on temperature. Together these results provide experimental proof that heterogeneous dynamical signatures near protein surfaces arise in part from chemical heterogeneity (energy disorder) as opposed to mere topological roughness of the protein surface.

Can models of charged rods show features of undercooled liquids?

We have performed molecular dynamic simulations of linear charged particle models. They are defined by rods with discrete charges at the ends. Intermolecular interactions are described by a coulombic term plus a Kihara potential for the rest of interactions. Our simulations were carried out for low and high charged systems either at thermodynamic states corresponding to the liquid branch of vapor–liquid equilibrium curve of non-charged rods or at supercritical temperatures of the non-charged systems. Our results show that rods with null or small discrete charge behave as normal liquids: the viscosity increases with rod length and they present short range velocity self-correlation function (VSCF). However, for medium and large discrete charges VSCF shows a very long range tail and the apparent viscosity increases by several orders of magnitude with a non-Arrhenius dependence with temperature. In some cases a transition from Arrhenius to non-Arrhenius behavior for medium charges is observed. Our results strongly suggest that systems behave as normal liquids when the rods have null or small charges and show undercooled liquid behavior for larger discrete charges at low temperatures.

Synthesis and Ionic Conductivity of Polymer Electrolytes Based on a Polyphosphazene with Short Side Groups

Random copolymers of the polyphosphazene [NPR2]n have been synthesized via living ionic polymerization with mixed substituents at the phosphorus atoms (i.e., R = bis(2-methoxy-ethyl)amino and n-propylamino). The polymers melt at 190 °C and start to decompose above 300 °C. Thin polymer electrolyte membranes were prepared by solution casting with dissolved lithium triflate (LiSO3CF3) and with NaI. The transparent membranes showed favorable mechanical properties below 100 °C. Tg values ranged between −50 and −36 °C. Membranes with 10 wt % LiSO3CF3 (corresponding to the atomic ratio Li/(O + N) = 1/30) showed rather low conductivities between 3.2 × 10-7 S cm-1 at 30 °C and 1.9 × 10-5 S cm-1 at 100 °C as determined from impedance measurements. The dispersion of 4 wt % Al2O3 nanoparticles in the polyphosphazene membranes with 10 wt % LiSO3CF3, however, leads to an increase of the conductivities by 2 orders of magnitude, that is, 1.0 × 10-5 S cm-1 at 30 °C and 1.5 × 10-3 S cm-1 at 100 °C. The heterogeneously doped salt-in-polymer membranes thus combine good mechanical stability with a high ionic conductivity. The temperature dependence of the conductivity data was analyzed in terms of the MIGRATION model, which gives a consistent explanation of the non-Arrhenius dependence.

Synthesis, characterization, and electrical, electrochemical and gas sensing properties of a novel ball-type four t-butylcalix[4]arene bridged binuclear zinc(ii) phthalocyanine

1,3 dimethoxy-4-t-butylcalix[4]arene has been used to synthesize a novel ball-type dimeric zinc(II) phthalocyanine, [Zn2Pc2(tbca)4] that exhibits mixed-valence behaviour and non-Arrhenius type dependence of conductivity.

Phase morphology and molecular dynamics of a polyurethane ionomer reinforced with a liquid crystalline filler

Solution-blended binary composites of ionic segmented polyurethane (SPU-I) and liquid crystalline oligomer (LCO) were characterized by wide-angle (WAXS) and small-angle (SAXS) X-ray scattering, differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and dielectric relaxation spectroscopy (DRS). Both components mutually influenced their states of aggregation in blends (most significantly, promoting smearing-out of interfaces between stiff and soft chain fragments of SPU-I into broad interfacial regions of intermediate composition). Apparently, the blend with w=0.10 happened to be most favorable for crystallization of the LCO, while the degree of microphase separation for SPU-I became lower and the distribution of stiff domains by sizes became broader, the higher the LCO content. The overall molecular mobility of SPU-I in blends was significantly reduced. This reduction included the intensity of the secondary and the primary relaxations, and of the interfacial Maxwell–Wagner–Sillars (MWS) relaxation, whereas the transition temperatures remained essentially composition-invariant. The Arrhenius-like behavior for the dc conductivity concomitant to the non-Arrhenius (i.e., Vogel–Tammann–Fulcher) frequency dependence for the α relaxation in blends suggested a decoupling of conductivity from the motion of the SPU-I soft chain segments.

Conductivity and Transport Properties of Aqueous Phosphotungstic and Silicotungstic Acid Electrolytes for Room-Temperature Fuel Cells

Conductivity measurements were performed on phosphotungstic and silicotungstic aqueous electrolyte solutions. The conductivity obtained from complex impedance plots had non-Arrhenius dependence on temperature and could be fit by the Vogel-Tamman-Fulcher expression, Conductivities reached 0.257 and at 298 K for the 60 wt % phosphotungstic and silicotungstic solutions, respectively. Low concentration silicotungstic solutions obeyed the Kohlrausch relation allowing for the determination of infinite dilution molar conductivity, with the anionic species having a molar conductivity of The diffusion coefficient of the anionic species at 303 K was with a hydrodynamic radius of 5.78 Å. Analysis of the charge transference numbers indicated that the conductivity was predominantly protonic, and suitable for room-temperature fuel cells. © 2003 The Electrochemical Society. All rights reserved.

Dielectric Relaxations in a Hyperbranched Polyester with Terminal Hydroxyl Groups: Effects of Generation Number

Relaxation processes in a hyperbranched polyester with terminal hydroxyl groups have been investigated. The study emphasizes the molecular weight dependence of conductivity and γ-relaxations as the α- and β-relaxations are masked by the conductivity. It is found that the conductivity relaxation follows a non-Arrhenius dependence while the γ-relaxation follows an Arrhenius dependence. There is a slight increase in the temperature location of the γ-relaxation with generation. The activation energies of the conductivity relaxation and γ-relaxation decrease with increasing generation number from the second to the fourth. This behavior is rationalized by relating molecular weight dependence of the chain end concentrations and possible conformational changes of the hyperbranched macromolecules.