共查询到20条相似文献,搜索用时 15 毫秒
1.
In this work, a numerical procedure based on the continuum model is developed and applied to the solvation energy for ground state and the spectral shift against the position and the orientation of the interfacial molecule. The interface is described as a sharp boundary separating two bulk media. The polarizable continuum model (PCM) allows us to account for both electrostatic and nonelectrostatic solute-solvent interactions when we calculate the solvation energy. In this work we extend PCM to the interfacial system and the information about the position and orientation of the interfacial molecule can be obtained. Based on the developed expression of the electrostatic free energy of a nonequilibrium state, the numerical procedure has been implemented and used to deal with a series of test molecules. The time-dependent density functional theory (TDDFT) associated with PCM is used for the electron structure and the spectroscopy calculations of the test molecules in homogeneous solvents. With the charge distribution of the ground and excited states, the position- and orientation-dependencies of the solvation energy and the spectrum have been investigated for the interfacial systems, taking the electrostatic interaction, the cavitation energy, and the dispersion-repulsion interaction into account. The cavitation energy is paid particular attention, since the interface portion cut off by the occupation of the interfacial molecule contributes an extra part to the stabilization for the interfacial system. The embedding depth, the favorable orientational angle, and the spectral shift for the interfacial molecule have been investigated in detail. From the solvation energy calculations, an explanation has been given on why the interfacial molecule, even if symmetrical in structure, tends to take a tilting manner, rather than perpendicular to the interface. 相似文献
2.
Analysis of the electrolyte diode. Electro-diffusion and chemical reaction within a hydrogel reactor
A reaction–diffusion system describing the electrolyte diode is investigated. This consists of a chemically crosslinked polyvinylalcohol (PVA) hydrogel cylinder in which a pH gradient is provided by having an acid and a base maintained at constant concentrations in reservoirs at each end of the one-dimensional reactor. A potential difference of a given strength is also applied across the gel cylinder. Previous experimental studies of the current–voltage characteristics (CVC) have shown two distinct cases, depending on whether a positive or negative potential difference was applied. The slopes of the linear current–voltage response curve are substantially different in the two cases, that in the 'forward' case being typically several orders of magnitude greater than that in the 'backward' case. Thus the system behaves like a semiconductor diode. The stationary concentration distribution for the different ions is described by a system of reaction–diffusion equations involving migration caused by the electric field. An approximate solution of these equations, using a simplified model, is presented and compared with results obtained by solving the full system numerically. The concentration profiles obtained from the numerical solution confirm the validity of the simplified model. 相似文献
3.
The Influence of Divalent Anions on the Rectification Properties of Nanofluidic Diodes: Insights from Experiments and Theoretical Simulations 下载免费PDF全文
Gonzalo Pérez‐Mitta Dr. Alberto G. Albesa Dr. María Eugenia Toimil Molares Prof. Dr. Christina Trautmann Prof. Dr. Omar Azzaroni 《Chemphyschem》2016,17(17):2718-2725
During the last decade, the possibility of generating synthetic nanoarchitectures with functionalities comparable to biological entities has sparked the interest of the scientific community related to diverse research fields. In this context, gaining fundamental understanding of the central features that determine the rectifying characteristics of the conical nanopores is of mandatory importance. In this work, we analyze the influence of mono‐ and divalent salts in the ionic current transported by asymmetric nanopores and focus on the delicate interplay between ion exclusion and charge screening effects that govern the functional response of the nanofluidic device. Experiments were performed using KCl and K2SO4 as representative species of singly and doubly charged species. Results showed that higher currents and rectification efficiencies are achieved by doubly charged salts. In order to understand the physicochemical processes underlying these effects simulations using the Poisson‐Nernst‐Planck formalism were performed. We consider that our theoretical and experimental account of the effect of divalent anions in the functional response of nanofluidic diodes provides further insights into the critical role of electrostatic interactions (ion exclusion versus charge screening effects) in presetting the ionic selectivity to anions as well as the observed rectification properties of these chemical nanodevices. 相似文献
4.
Computational models including electrode polarization can be essential to study electrode/electrolyte interfacial phenomena more realistically. We present here a constant-potential classical molecular dynamics simulation method based on the extended Lagrangian formulation where the fluctuating electrode atomic charges are treated as independent dynamical variables. The method is applied to a graphite/ionic liquid system for the validation and the interfacial kinetics study. While the correct adiabatic dynamics is achieved with a sufficiently small fictitious mass of charge, static properties have been shown to be almost insensitive to the fictitious mass. As for the kinetics study, electrical double layer (EDL) relaxation and ion desorption from the electrode surface are considered. We found that the polarization slows EDL relaxation greatly whereas it has little impact on the ion desorption kinetics. The findings suggest that the polarization is essential to estimate the kinetics in nonequilibrium processes, not in equilibrium. © 2019 Wiley Periodicals, Inc. 相似文献
5.
D. Megías-Alguacil F. J. Arroyo F. Carrique A. V. Delgado 《Colloid and polymer science》2000,278(7):647-653
This article describes an experimental and theoretical investigation of the so-called primary electroviscous effect, i.e.,
the increase in suspension viscosity due to the existence of an electrical double layer around the particles. By measuring
the viscosity of ethylcellulose latex suspensions, the electroviscous coefficient, the quantity measuring the effect, was
estimated for different concentrations of 1-1 electrolyte in the dispersion medium. These data were compared with the predictions
of Watterson and White's model, using the zeta potential of the particles deduced from electrophoretic mobility measurements.
It was found that the theory considerably underestimates the effect. In an attempt to improve the agreement between data and
predictions, the model was generalized to include the possibility (dynamic Stern layer) that ions in the inner part of the
double layer have nonzero mobility. The general theory, however, predicts even lower values of the electroviscous coefficients,
thus increasing the separation between calculated and measured electroviscous coefficients. A careful analysis of the ionic
concentrations and velocity profiles with and without dynamic Stern layer corrections can account for this fact, but leaves
unsolved the problem of the large discrepancies found in the theoretical explanation of the strength of the electroviscous
effect.
Received: 19 October 1999/Accepted: 17 December 1999 相似文献
6.
Ping Chen Jing Wang Baichen Wang Wei Li Chengshuang Zhang Hong Li Baolei Sun 《Surface and interface analysis : SIA》2009,41(1):38-43
Interfacial adhesion between the fiber and the matrix in a composite is a primary factor for stress transfer from the matrix to the fiber. In this study, oxygen plasma treatment method was applied to modify the fiber surface for improving interfacial adhesion of aramid fiber‐reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite. Composite interfacial adhesion properties were determined by interlaminar shear strength (ILSS) using a short‐beam bending test. The composite interfacial adhesion mechanism was discussed by SEM. The changes of chemical composition and wettability for plasma‐treated fiber surfaces stored in air as long as 10 days were investigated by XPS and dynamic contact angle analysis (DCAA), respectively. Results indicated that oxygen plasma treatment was an effective method for improving interfacial adhesion; plasma‐treated fiber surface suffered aging effects during storage in air. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
7.
Dr. Matthew A. Brown Alok Goel Prof. Dr. Zareen Abbas 《Angewandte Chemie (International ed. in English)》2016,55(11):3790-3794
The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO2) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles’ surface potential by X‐ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased. 相似文献
8.
The relationships among cure temperature, chemical kinetics, microstructure, and mechanical performance have been investigated for vinyl–ester resins. Fourier transform infrared spectroscopy was used to follow the reactions of vinyl–ester and styrene during isothermal curing of Dow Derakane 411‐C‐50 at 30 and 90°C. Reactivity ratios of vinyl–ester and styrene vinyl groups were evaluated using the copolymer composition equation. The results indicate that the ratio of vinyl–ester to styrene double bonds incorporated into the network is greater for 30 than for 90°C cure. Mechanical properties were obtained for systems subjected to isothermal cures at 30 and 90°C and postcured above ultimate Tg. The results show that the initial cure temperature significantly affects the mechanical behavior of vinyl–ester resin systems. In particular, values of strength and fracture toughness for postcured samples initially cured isothermally at 30°C are significantly higher than those obtained for samples cured isothermally at 90°C. Examination of fracture surfaces using atomic force microscopy revealed the existence of a nodular microstructure possessing characteristic nodule dimensions that are affected by the temperature of cure. Such features suggest the existence of phase separation during cure. A binary interaction model in conjunction with chemical kinetic data and estimated solubility parameters was used to evaluate enthalpic interactions between the growing polymer network and monomers of the vinyl–ester system. The results indicate that the interaction energy becomes increasingly endothermic as cure progresses and that this energy is affected by the temperature of cure through differences in copolymerization behavior. Hence, in addition to entropic factors, the changes in enthalpic contribution to the Gibbs free energy suggest that the probability of phase separation increases with extent of cure and that its onset is potentially affected by cure temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 725–744, 1999 相似文献
9.
As a new type of green environment‐friendly cementitious material, microbial‐induced mineralization products have garnered more and more attention. In this paper, the synthesis of mineralization products under microbial inducement was conducted. The composition and microstructure of mineralization products were studied using energy‐dispersive spectrometer (EDS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results showed that mineralization products were calcite, while the shape was similar to globular type, and particle size was about 5 μm. The effect of microbial culture solution, secretion solution, and concentration on the conductivity of the solution was compared and analyzed. During the formation of mineralization products, bacterial bodies not only played the role of nucleation sites but also accelerated the deposition of mineralization products. Thus, it could be seen that the bacterial bodies had a certain influence on the reaction kinetics. The adhesion force of mineralization products was evaluated by the interfacial adhesion properties between the mineralization products and glass slides. The results of the sonication test and scratch test indicated that the interfacial adhesion strength between mineralization products and glass slides was closely related to the mass of mineralization products deposited. The larger the mass of mineralization products deposited, the greater the interfacial adhesion strength. Based on the above research and analysis, the reaction process and mechanism model of microbial‐induced mineralization were defined. 相似文献
10.
Ran Y. Suckeveriene Ron Rahman Irina Shtein Nadia Kharlamova Moshe Narkis 《先进技术聚合物》2012,23(12):1536-1542
This paper summarizes a study on emulsifier‐free ultrasonically assisted in situ dynamic interfacial emulsion copolymerization process of acrylamide and styrene. The resulting emulsions are stable and uniform for several months. Thermogravimetric analysis (TGA) curves and reaction conversion measurements have provided an important knowledge regarding the emulsifier‐free polymerization method. Solvent extractions (water, methanol, and xylene) have shown that the polymerization product is essentially a styrene–acrylamide copolymer. The copolymer produced is a block copolymer, PS‐b‐PAM, where each block contains small amounts of the other comonomer. The produced emulsions are film forming at room temperature in spite of the very high block Tgs, owing to a unique water plasticization effect of the polyacrylamide blocks. Some films prepared from the PS‐b‐PAM have resulted in clear and transparent films. The presented interfacial dynamic polymerization process is fast, reaching 81% conversion within 2 hr of sonication at 4°C (low temperature owing to molecular weight and kinetic considerations), and produces very stable PS‐b‐PAM emulsions. TGA was extensively used as an analytical tool for determination of the reaction parameters and composition of the acrylamide–styrene copolymers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
11.
Joydeb Chanda Pulok K. Mukherjee Rajarshi Biswas Dipankar Malakar Manoj Pillai 《Biomedical chromatography : BMC》2019,33(4)
The different parts of Momordica charantia have been reported to have several therapeutic applications against hyperglycemia and hypercholesterolemia associated with pancreatic lipase (PL). Inhibition of this enzyme prevents the absorption of dietary triglyceride in the intestine, and thus exerts an anti‐obesity effect. This study aimed to investigate the bioactive constituents of the fruits of M. charantia (MCF) extract and fractions against pancreatic PL followed by study of their inhibition kinetics. The PL inhibitory assay was performed spectrophotometrically by measuring the change in absorbance of the products at 405 nm, using p‐nitrophenylcaprylate as substrate. The results indicated that the ethyl acetate fraction of MCF (EFMC) offered significant, dose‐dependent inhibition against PL, compared with the positive control, Orlistat. The enzyme kinetics study revealed the inhibition to be a mixed type in nature. Additionally, the total phenol and flavonoid content of the fractions was estimated. A positive correlation between phenolic content of EFMC and its PL inhibitory activity was established statistically, which implied that higher inhibition potential was contributed by the phenolic compounds. The identification of the bioactive constituents was further confirmed by LC–QTOF–MS study. This finding suggested that phenolic compounds of MCF can serve as functional food components to address obesity‐related disorders linked with PL. 相似文献
12.
3-(二氰亚甲基)-5,5-二甲基-1-(3-[9-(2-乙基-己基)-咔唑基]-乙烯基)环己烷(DCDHCC)是一种用于光电器件中的有机染料,它具有良好的发光特性.我们使用含时密度泛函方法(TD-PBE0,TD-BMK和TD-M06)以及极化连续模型(PCM)计算了该材料在溶剂中的吸收和发射特性.计算中使用了线性响应(LR)、态定(SS)两种溶剂模型和6-31G(d)、6-31+G(d,p)两种基组.计算了DCDHCC在苯、四氢呋喃和丙酮溶剂中的吸收和发射光谱,并与实验观测进行了比较.结果表明:对于吸收光谱的计算,杂化函数的影响大于基组和溶剂模型,在三种函数中BMK更适于研究DCDHCC的吸收光谱;而对于发射光谱,基组的影响最大,基组通过影响激发态构型从而影响发射光谱,对于激发态构型的优化需要使用6-31+G(d,p)基组.我们希望这些研究能对今后设计类似的发光分子有帮助. 相似文献
13.
S. L. Khursan A. M. Nazarov E. M. Chainikova V. D. Komissarov 《Russian Chemical Bulletin》2001,50(5):793-797
The absorption spectra and rate constants of diphenylcarbonyl oxide recombination in a series of solvents and their binary mixtures were determined by flash photolysis. An increase in the solvent polarity causes hypsochromic shift of the maximum in the absorption spectrum of Ph2COO. The analysis of the solvent effect on the recombination rate constant in terms of the four-parameter Koppel—Palm equation shows that the reactivity of carbonyl oxide depends on both specific and non-specific solvations. Quantum chemical B3LYP/6-31G(d) calculations of H2COO and PhHCOO carbonyl oxides as well as the complexes of H2COO with acetonitrile and ethylene in different media were performed using a polarized continuum model. 相似文献
14.
W. Van der Vegt H. C. Van der Mei Dr. H. J. Busscher W. Norde 《Colloid and polymer science》1996,274(1):27-33
Interfacial tension changes during protein adsorption at both the solid-liquid and the liquid-vapor interface were measured simultaneously by ADSA-P from sessile droplets of protein solutions on fluoroethylenepropylene-Teflon. Four globular proteins of similar size, viz. lysozyme, ribonuclease, -lactalbumin and Ca2+-free -lactalbumin, and one larger protein, serum albumin, were adsorbed from phosphate solutions at varying pH values (pH 3-12). The kinetics of the interfacial tension changes were described using a model accounting for diffusion-controlled adsorption of protein molecules and conformational changes of already adsorbed molecules. The contribution of conformational changes to the equilibrium interfacial pressure was shown to be relatively small and constant with respect to pH when compared to the contribution of adsorption of the protein molecules. The model also yields the diffusion relaxation time and the rate constant for the conformational changes at the interface. Around the isoelectric point of a protein the calculated diffusion relaxation time was minimal, which is ascribed to the absence of an energy barrier to adsorption. Energy barriers to adsorption become larger at pH values away from the isoelectric point and can therefore become rate-limiting for the adsorption process. The rate constants for conformational changes at the liquid-vapor interface were maximal around the isoelectric point of a protein, suggesting a smaller structural stability of the adsorbed protein. At the solid-liquid interface the rate constants were smaller and independent of pH. indicating that conformational changes more readily occur at the liquid-vapor than at the solid-liquid interface. 相似文献
15.
R. A. Shagidullina L. Ya. Zakharova L. A. Kudryavtseva 《Russian Chemical Bulletin》1999,48(2):279-281
Study of the kinetics of alkaline hydrolysis of alkylp-nitrophenyl chloromethylphosphonates in micellar solutions of cetylpyridinium bromide showed that the observed rate constant
depends on the hydrophobicity of the substrates. A minor increase in the length of the alkyl chain in the substituent increases
the catalytic effect in the series Et<Bu<C6H13. Further increase in the substrate hydrophobicity results in a decrease in the bimolecular rate constant in the micellar
phase.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 279–282, February, 1999. 相似文献
16.
Odriozola G Schmitt A Callejas-Fernández J Hidalgo-Alvarez R 《Journal of colloid and interface science》2007,310(2):471-480
We report zeta potential and aggregation kinetics data on colloidal latex particles immersed in water-alcohol media. Zeta potential values show absolute maxima for volume fractions of alcohol of 0.10 and 0.05 for ethanol and 1-propanol, respectively. For methanol, no maximum of the absolute value of the zeta potential was found. Aggregation kinetics was studied by means of a single-cluster optical sizing equipment and for alcohol volume fractions ranging from 0 to 0.1. The aggregation processes are induced by adding different potassium bromide concentrations to the samples. We expected to find a slowdown of the overall aggregation kinetics for ethanol and 1-propanol, and no significant effect for methanol, as compared with pure water data. That is, we expected the zeta potential to govern the overall aggregation rate. However, we obtained a general enhancement of the aggregation kinetics for methanol and 1-propanol and a general slowdown of the aggregation rate for ethanol. In addition, aggregation data under ethanol show a slower kinetics for large electrolyte concentration than that obtained for intermediate electrolyte concentration. We think that these anomalous behaviors are linked to layering, changes in hydrophobicity of particle surfaces due to alcohol adsorption, complex ion-water-alcohol-surface structuring, and competition between alcohol-surface adsorption and alcohol-alcohol clustering. 相似文献
17.
Shizhou Fu Wu Zhou Zhongni Wang Baolin Yin Jie Liu Dezhi Sun Xilian Wei 《Fluid Phase Equilibria》2008,269(1-2):93-97
Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R12HTAB) and n-hexane were measured using the spinning drop method. The effects of the R12HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, Da, and the adsorption barrier, a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while a becomes higher with increasing R12HTAB concentration in the bulk aqueous phase. Da decreases from 5.56 × 10−12 m−2 s−1 to 0.87 × 10−12 m−2 s−1 while a increases from 5.41 kJ mol−1 to 7.74 kJ mol−1 with the increase of concentration in the bulk solution of R12HTAB from 0.5 × 10−3 mol dm−3 to 4 × 10−3 mol dm−3. Change of temperature affects the adsorption rate through altering Da and a. The value of Da increases from 5.56 × 10−12 m−2 s−1 to 13.98 × 10−12 m−2 s−1 while that of a decreases from 5.41 kJ mol−1 to 5.07 kJ mol−1 with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules. 相似文献
18.
Surfactants such as quaternary ammonium salts (QAS) have been in increasing demand, for emerging new applications. Recent attempts at process intensification of their production have disclosed the need for a better understanding of QAS thermal stability. This work aims to determine the degradation kinetics of various QASs and the associated solvent effects. The degradation kinetics of four methyl carbonate QASs were determined in various polar solvents in stainless steel batch autoclaves. H NMR spectrometry was employed for offline analysis of the reaction mixtures. The kinetic parameters were then used to compare the thermal stability of the four compounds in the polar solvents. Water showed no degradation, and methanol (MeOH) was the solvent that provided the second-best stability. Water–MeOH mixtures may provide an overall optimum. Moreover, and longer long-chain substituents increased the degradation rate. Thermogravimetric analysis was used to obtain the thermal stability in a solid state, that is, solventless environment. Isoconversional analysis showed that no reliable kinetic parameters could be determined. Nevertheless, the data did allow for a comparison of the thermal stability of 14 different QASs. Furthermore, the relative instability of the compounds in the solid state demonstrated the challenges of solventless QAS production. 相似文献
19.
You‐Pin Gong Ai‐Dong Li Xiao‐Jie Liu Wen‐Qi Zhang Hui Li Di Wu 《Surface and interface analysis : SIA》2011,43(3):734-737
The GaAs surfaces were passivated by two kinds of chemical pretreatments (using NH4OH and (NH4)2S as passivation agents) for atomic layer deposited (ALD) Al2O3 dielectric film growth. The chemical information at Al2O3/GaAs interfaces was carefully characterized. The impact of surface treatments on the band alignments of ALD Al2O3 films on n? GaAs (100) substrates was also investigated. After postdeposition annealing, the NH4OH passivated samples not only have a slight increase of the As? As peaks with an appearance of As suboxide (AsOx) feature at Al2O3/GaAs interfaces but also exhibit a serious interfacial interdiffusion between Al2O3 and GaAs. However, the (NH4)2S passivated samples produce the Ga? S and As? S overlayers on GaAs, effectively preventing from the intermixed diffusion between Al2O3 films and GaAs substrates with a sharper interface. Both NH4OH and (NH4)2S passivated Al2O3 samples show the same band gap of 6.67 eV. The conduction band offset at Al2O3/GaAs interface for the (NH4)2S passivated samples have a slight enhancement of 0.14 eV in comparison to NH4OH passivated ones. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
Katsunari Kataoka Asuka Harada Toshikazu Tamai Qui Tran-Cong 《Journal of Polymer Science.Polymer Physics》1998,36(3):455-462
Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch–Williams–Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the “shallow quench” conditions in the region far away from the coexistence curve of the reacting blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 455–462, 1998 相似文献