Reaction Time Constant Research Articles

Physical analysis of self-discharge mechanism for supercapacitor electrode for hybrid electric energy storage system

Self-discharge is a spontaneous process that has considerable adverse effects on the performance of supercapacitors. In order to quantitatively investigate the contribution of self-discharge mechanism, this paper proposed a theoretical self-discharge model for carbon electrode of supercapacitors based on electric double layer theory. Three physical contributions, i.e., side reactions, ion diffusion, and ohmic leakage, were investigated. In addition, self-discharge measurement of carbon electrode was performed to validate such theoretical model. The results indicated that the potential drop due to side reactions was negligible throughout the self-discharge process in all cases. In addition, ion diffusion dominated for low initial potential and short holding time, accounting for 50%–80% of self-discharge. On the other hand, ohmic leakage dominated for high initial potential and long holding time. Furthermore, the potential drop due to ion diffusion increased monotonously with time while the potential drop due to ohmic leakage remained constant throughout the self-discharge. Moreover, the potential drop due to ohmic leakage increased with the increase in holding time, which compensated for the decreasing potential drop due to ion diffusion. This could explain the fact that the total electrode potential decay during the self-discharge was independent of holding time. Finally, dimensional analysis was performed to predict self-discharge. Time constants of side reactions, ion diffusion, and ohmic leakage were derived. Overlapping dimensionless electrode potential versus dimensionless time indicated that such dimensional analysis was generally applicable to predict self-discharge of carbon-based supercapacitors at a given initial potential and time.

Effects of Molecular Structure on Organic Contaminants' Degradation Efficiency and Dominant ROS in the Advanced Oxidation Process with Multiple ROS.

In this study, the previously overlooked effects of contaminants' molecular structure on their degradation efficiencies and dominant reactive oxygen species (ROS) in advanced oxidation processes (AOPs) are investigated with a peroxymonosulfate (PMS) activation system selected as the typical AOP system. Averagely, degradation efficiencies of 19 contaminants are discrepant in the CoCaAl-LDO/PMS system with production of SO4•-, •OH, and 1O2. Density functional theory calculations indicated that compounds with high EHOMO, low-energy gap (ΔE = ELUMO - EHOMO), and low vertical ionization potential are more vulnerable to be attacked. Further analysis disclosed that the dominant ROS was the same one when treating similar types of contaminants, namely SO4•-, 1O2, 1O2, and •OH for the degradation of CBZ-like compounds, SAs, bisphenol, and triazine compounds, respectively. This phenomenon may be caused by the contaminants' structures especially the commonly shared or basic parent structures which can affect their effective reaction time and second-order rate constants with ROS, thus influencing the contribution of each ROS during its degradation. Overall, the new insights gained in this study provide a basis for designing more effective AOPs to improve their practical application in wastewater treatment.

Optical and Structural Characteristics of PANI capped PbS Nanoparticles

The modern research communities are now-a-days immensely attracted towards the semi-conductor nanoparticles due to their budding application in both traditional optical devices and new generation of nano-electronic and nano-optoelectronic devices because of their unexpected chemical and physical properties. In this present work, Lead Sulphide (PbS) nanoparticles with diameter in the range of 26–58 nm were synthesized by varying concentration of the conducting matrix Poly-aniline (PANI), using a wet Chemical technique in a non-acidic medium. The precursors used here are Lead Nitrate (Pb(NO3)2) and Sodium Sulphide (Na2S). Polyaniline (PANI) has been used as a conductive capping agent. PbS is synthesized by varying the concentration of conducting matrix PANI while keeping the reaction time constant (i.e 3 hrs). The PANI concentration has been changed from 0.5 gm to 2.0 gm in 5 different samples. Finally the synthesized samples are characterized by using various characterization techniques such as UV–Vis Spectroscopy (UV), Photoluminescence Spectroscopy (PL), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-rayAnalysis (EDAX) and Transmission Electron Microscopy (TEM).

Laser direct submicron fabrication by controlling reaction time constant of photoresist

This paper focuses on fabrication of submicron structures onto photoresist films by use of a continuous wave (CW) laser. Conventional CW laser fabrication has low accuracy, because the laser beam affects the periphery of a beam exposed area; it is unsuitable for three-dimensional submicrofabrication. Therefore, we have developed a high-accuracy exposure method with CW lasers that use controlling the reaction time constant of photoresists. This method makes it possible to restrict the exposure area by making the response of the photochemical reaction depend on the exposure intensity nonlinearly. In our study, we realized to expose the line pattern having 180 nm minimum width, which is smaller than the focused beam spot diameter, by using the CW laser with wavelength of 532 nm.

Effect of the transition rate between two excited states on the spectral dynamics of dual fluorescence: Blurring of the isoemissive point

We study the fluorescence spectral dynamics of a molecule with two excited fluorescent states (called the precursor and product) within the stochastic point transition model, which includes a consistent description of the dynamics of the particles distribution in excited states and transitions between them. Crucial changes in spectral dynamics with increasing the transition rate between the precursor and the product are discovered. Analysis of the results of spectral dynamics modeling allows us to determine how the transition rate between the precursor and the product affects the isoemissive point in the spectra collected with an increasing time delay. The following main regularities were revealed: fluorescence spectra with a short delay not exceeding several solvent relaxation times (τL) may not pass through the isoemissive point; the isoemissive point shifts to the red with a decrease in reaction time constant (τeff). The shifted isoemissive point exists in the range 10τL<τeff<40τL. For faster reactions with 5τL<τeff<10τL, the isoemissive point blurs. When the reaction proceeds in the ultrafast regime τeff<5τL, the fluorescence spectrum shifts from a vicinity of the precursor spectrum to the product spectrum as a whole, changing its shape.

(Invited) On Deconvoluting the Contributions of the Cathode and Anode to SOFC Electrode Performance

In SOFC research, it is well know that deconvoluting the contributions of the cathode and anode to the total electrode performance is of significant importance, but is also extremely challenging because of the overlap of reaction time constants from both electrodes. Due to the difficulty in placing a reference electrode, currently there are two approaches to address this challenge. The first approach is to use the distribution of relaxation times (DRT) to analyze the spectra acquired from electrochemical impedance spectroscopy (EIS). The second method is to measure the SOFC performance by changing the oxygen partial pressure while other operating parameters are fixed. In doing so, one assumes that the changes in EIS spectra are resulted from the change of cathode performance. In this presentation, a theoretical model is developed to show what the requirements are for this assumption. Various cathode- and anode- materials are then utilized to validate our theoretical analysis. DRT analysis is used to cross validate this model. Criteria on deconvoluting electrode performance will be provided.

Assessment of biomass alterations during hydrothermal pretreatment by in-situ dynamic mechanical analysis

This work proposes an original innovative in-house device able to characterize the evolution of viscoelastic properties of lignocellulosic products during hydrothermal pretreatment (water-saturated conditions up to 190 °C). The main objective is to assess the cooking phase before steam explosion. We designed and built a novel experimental device for analyzing the dynamic mechanical analysis of the biomass soaked in water or acidic water. The device allows the sample to be loaded/unloaded during the test with an accurate measurement of deformation and force despite the severe conditions. This system can perform the mechanical test on immersed samples under controlled pressure (up to 1.5 MPa) and temperature (up to 190 °C). Experiments were performed with poplar via harmonic and periodic tests. The experimental data collected on poplar allows the characteristic time constants of the thermo-chemical reactions to be obtained as a function of the operating conditions.

Engineering Functions into Platinum and Platinum-Rhodium Nanoparticles in a One-Step Microwave Irradiation Synthesis.

Platinum (Pt) and platinum–rhodium (PtRh) nanoparticles (NPs) are active catalysts for a range of important industrial reactions, and their response has been shown to be affected by size, morphology, composition, and architectural configuration. We report herein the engineering of these functionalities into NPs by suitably modifying our single‐step fabrication process by using microwave irradiation dielectric heating. NPs with different morphologies are acquired by manipulating the reaction kinetics with the concentration of the capping agent while keeping the reaction time constant. Pt@Rh core@shell octopod‐cube, Pt‐truncated‐cube, and cube and small‐sphere NPs having “near‐monodisperse” distributions and average sizes in the range of 4 to 18 nm are obtained. By increasing the microwave time the composition of Pt@Rh can be tuned, and NPs with a Rh‐rich shell and a tunable Pt100−xRhx (x≤41 at %) core are fabricated. Finally, alloy bimetallic PtRh NPs with controlled composition are designed by simultaneous tuning of the relative molar ratio of the metal precursors and the microwave irradiation time.

Preparation and photochromic properties of pyrazolones/polyvinyl alcohol composite films

Novel photochromic composite films have been successfully fabricated by dispersing pyrazolone derivative: 1,3-Diphenyl-4-(3-chlorobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (1a) into hydrosol of polyvinyl alcohol (PVA). The microstructure, photochromic behaviors and thermal bleaching properties were investigated by Raman spectroscopy, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet–visible absorption spectroscopy (UV–vis). The results showed that 1a was not only blended but also well dispersed in the PVA polymer films with a suitable content of chromophore. Upon UV light irradiation, the composite films gradually changed from colorless to yellow and recovered fully to the initial state upon thermal bleaching. The time constants of photochromic reactions were almost the same as those of 1a observed in their crystalline state, indicating that the photochromic phenomenon is barely disturbed by the polymer matrix.

Fabrication of moth-eye structure on photoresist film by laser control of reaction time constant

ABSTRACTWe have proposed the fabrication of high-contrast-moth-eye structure using continuous wave (CW) laser. Nonlinear-optical reaction time constant of the photoresist can be controlled by manipulating the exposure intensity and scanning speed of the laser. As a result, shortening the time constant in the intense beam area and lengthening that in the weak beam area compared with the scanning speed, we can limit the exposed area.

Optimization of Alkali Catalyzed Transesterification of Safflower Oil for Production of Biodiesel

The Central Composite Design is used for the optimization of alkaline catalyzed transesterification parameters such as methanol quantity, catalytic concentration, and rotational speed by keeping the temperature and reaction time constant. The Central Composite Design method is employed to get the maximum safflower oil methyl ester yield. The combined effects of catalyst concentration, rotational speed, and molar ratio of alcohol to oil were investigated and optimized using response surface methodology. A statistical model has predicted the maximum yield of safflower oil methyl ester (94.69% volume of oil) parameters such as catalyst concentration (0.6 grams), methanol amount (30 mL), rotational speed (600 rpm), and keeping constant reaction temperature (55°C to 65°C) and reaction time (60 minutes). Experimental maximum yield of 91.66% was obtained at above parameters. XLSTAT is used to generate a linear model to predict the methyl ester yield as a function of methanol quantity, catalyst concentration, and rotational speed by keeping constant reaction temperature (55°C to 65°C) and reaction time (60 minutes). MINITAB is used to draw the 3D response surface plot and 2D contour plot to predict the maximum biodiesel yield.

Membrane-mediated amyloid formation of PrP 106–126: A kinetic study

PrP 106–126 conserves the pathogenic and physicochemical properties of the Scrapie isoform of the prion protein. PrP 106–126 and other amyloidal proteins are capable of inducing ion permeability through cell membranes, and this property may represent the common primary mechanism of pathogenesis in the amyloid-related degenerative diseases. However, for many amyloidal proteins, despite numerous phenomenological observations of their interactions with membranes, it has been difficult to determine the molecular mechanisms by which the proteins cause ion permeability. One approach that has not been undertaken is the kinetic study of protein–membrane interactions. We found that the reaction time constant of the interaction between PrP 106–126 and membranes is suitable for such studies. The kinetic experiment with giant lipid vesicles showed that the membrane area first increased by peptide binding but then decreased. The membrane area decrease was coincidental with appearance of extramembranous aggregates including lipid molecules. Sometimes, the membrane area would increase again followed by another decrease. The kinetic experiment with small vesicles was monitored by circular dichroism for peptide conformation changes. The results are consistent with a molecular simulation following a simple set of well-defined rules. We deduced that at the molecular level the formation of peptide amyloids incorporated lipid molecules as part of the aggregates. Most importantly the amyloid aggregates desorbed from the lipid bilayer, consistent with the macroscopic phenomena observed with giant vesicles. Thus we conclude that the main effect of membrane-mediated amyloid formation is extraction of lipid molecules from the membrane. We discuss the likelihood of this effect on membrane ion permeability.

Definition of kinetic characteristics of biochemical oxidation of substances of sewage butter-fat industries

The analysis of existing methods of sewage treatment of butter-fat industries, that the most effective way - biological clearing. Experimental studying kinetic oxidations represents the big practical interest. Authors receive for the first time constants of the equations enzyme process reactions of own-step biological sewage treatment of butter-fat industries.

Enzyme kinetics determined by single-injection isothermal titration calorimetry

The purposes of this paper are (a) to examine the effect of calorimeter time constant (τ) on heat rate data from a single enzyme injection into substrate in an isothermal titration calorimeter (ITC), (b) to provide information that can be used to predict the optimum experimental conditions for determining the rate constant (k2), Michaelis constant (KM), and enthalpy change of the reaction (ΔRH), and (c) to describe methods for evaluating these parameters. We find that KM, k2 and ΔRH can be accurately estimated without correcting for the calorimeter time constant, τ, if (k2E/KM), where E is the total active enzyme concentration, is between 0.1/τ and 1/τ and the reaction goes to at least 99% completion. If experimental conditions are outside this domain and no correction is made for τ, errors in the inferred parameters quickly become unreasonable. A method for fitting single-injection data to the Michaelis–Menten or Briggs–Haldane model to simultaneously evaluate KM, k2, ΔRH, and τ is described and validated with experimental data. All four of these parameters can be accurately inferred provided the reaction time constant (k2E/KM) is larger than 1/τ and the data include enzyme saturated conditions.

Kinetics study of living microemulsion polymerization mediated by reversible addition-fragmentation chain transfer

Reversible addition-fragmentation chain transfer (RAFT) polymerization is usually carried out in emulsion or miniemulsion, often encounters problems of rate retardation, phase separation, and loss of activity in these systems. Compared with emulsion or miniemulsion, microemulsion remains stable during polymerization because of presence of large amount surfactant that promotes formation of large number of monomer swollen micelles. Therefore, microemulsion typically shows fast polymerization rate and produces latex nanoparticles composed of high molecular weights polymers. Until now, only few RAFT polymerizations have been successfully conducted in microemulsion and related kinetics studies are very limited. Here, kinetics studies on RAFT microemulsion polymerization were carried out and the factors that affected kinetics were detailedly investigated. Kinetic parameters, theoretical molecular weights, chain transfer constant, propagate rate constant, half reaction time and polymerization rate constant were all calculated. Experimental results indicated temperature and concentration of chain transfer agent were important factors which influenced polymerization kinetics. In addition, the chemical structure of chain transfer agent, molecular weights and its distribution, and the morphologies structure of polymers were characterized by 1H NMR, FT-IR, GPC and TEM, respectively.

Enhanced Sensitivity of Pt/NiO Gate Based AlGaN/GaN C-HEMT Hydrogen Sensor

In this article we demonstrate the high sensitivity AlGaN/GaN circular HEMT (C-HEMT) hydrogen gas sensor with new gate interfacial Pt/NiO layer. The wide band-gap III-nitride semiconductor heterostructure allows the sensor operation at elevated temperatures. Likewise, the C-HEMT sensing device is easy to prepare because the MESA insulation step can be omitted. Moreover, the I-V characteristics of ring gate diodes with a dominant thermionic emission of electrons can be easly achieved by elimination of tunneling currents induced on the MESA-etched edges. The Pt/NiO stacked gate absorption layer has nanocrystalline structure, what increases the surface-to-volume ratio. Consequently, the hydrogen gas is more efficiently dissociated at low temperature. Comparing to reference Pt/AlGaN/GaN diode sensor, the optimum operation temperature decreases from 250 oC towards 50oC and the hydrogen detection efficiency is enhanced about 10 times. This is desirable for battery-powered sensors with low current consumption. On the other hand, the fabricated sensor shows longer reaction and regeneration time constants. This is due to longer diffusion path that hydrogen atoms must overcome to reach the AlGaN semiconductor surface.

Submicron Channel Fabrication in Photoresist Film Using Continuous Wave Laser

Laser fabrication of submicron hollow channel using a continuous wave (CW) light source is investigated. In conventional laser fabrication, CW laser beam affects the immediate vicinity of a beam exposure area because the fabrication employs a heat mode process. Our method proposed, however, three-dimensionally localizes the exposure area in a focal plane by controlling the reaction time constant of a photoresist film. As a result, we have fabricated a submicron hollow channel in the photoresist film using the CW laser source.

Hollow tube fabrication in photoresist film using continuous wave laser

This paper is a study of three-dimensional (3D) micron/submicron fabrication with a continuous wave (CW) laser. The fabrication forms vertical and horizontal hollow tubes in a photoresist film with nonlinear optical properties. We controlled beam intensities and dose amounts to manipulate a reaction time constant of the photoresist; we fabricated the 3D hollows in high contrast.

Excited-State Intermolecular Proton Transfer of Firefly Luciferin V. Direct Proton Transfer to Fluoride and Other Mild Bases

We studied the direct proton transfer (PT) from electronically excited D-luciferin to several mild bases. The fluorescence up-conversion technique is used to measure the rise and decay of the fluorescence signals of the protonated and deprotonated species of D-luciferin. From a base concentration of 0.25 M or higher the proton transfer rates to the fluoride, dihdyrogen phosphate or acetate bases are fast and comparable. The fluorescence signals are nonexponential and complex. We suggest that the fastest decay component arises from a direct proton transfer process from the hydroxyl group of D-luciferin to the mild base. The proton donor and acceptor molecules form an ion pair prior to photoexcitation. Upon photoexcitation solvent rearrangement occurs on a 1 ps time-scale. The PT reaction time constant is ∼2 ps for all three bases. A second decay component of about 10 ps is attributed to the proton transfer in a contact pair bridged by one water molecule. The longest decay component is due to both the excited-state proton transfer (ESPT) to the solvent and the diffusion-assisted PT process between a photoacid and a base pair positioned remotely from each other prior to photoexcitation.

Excited state charge transfer reaction in (mixed solvent + electrolyte) systems: Role of reactant–solvent and reactant–ion interactions

Fluorescence spectroscopic techniques have been used to study the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in two sets of mixed solvents, (1-propanol + ethyl acetate) and (propylene carbonate + acetonitrile), in the absence and presence of a strong electrolyte, lithium perchlorate. These two sets of mixed solvent systems represent binary solvent mixtures of low and high polarities, respectively. Density, sound velocity and viscosity measurements indicate that these two mixed solvent systems are structurally different. Stronger ion-reactant interaction is evidenced in the mole fraction independence of emission frequencies in electrolyte solutions of low polar binary solvent mixtures. For both these mixtures, the reaction driving force (− ΔG r ) decreases with increase in mole fraction of the relatively less polar solvent component of the mixture. Interestingly, − ΔG r increases significantly on addition of electrolyte in low polar mixtures and exhibits mixture composition dependence but, in contrast, − ΔG r in high polar mixtures does not sense variation in mixture composition in presence of electrolyte. This insensitivity to mixture composition for high polar mixtures is also observed for the measured reaction time constant. In addition, the reaction time constant does not sense the presence of electrolyte in the high polar solvent mixtures. The reaction time constant in low polar mixtures, which becomes faster on addition of electrolyte, lengthens on increasing the mole fraction of the relatively less polar solvent component of the mixture. These observations have been qualitatively explained in terms of the measured solvent reorganization energy and reaction driving force by using expressions from the classical theory of electron transfer reaction.