Gibbs Excess Research Articles

Effect of ethanol on wetting and adhesion properties of rhamnolipid

The wetting and adhesion properties of the surfactants and biosurfactants play a very important role in the processes occurring in practice. These properties can be changed by the addition to the aqueous solution of the surfactants and biosurfactants different kinds of the substances influencing the structure of water and the hydration of the head and tail of the surfactants molecules. Therefore, we studied effect of the ethanol on the wetting and adhesion properties of rhamnolipid by the measurements of the contact angle of the aqueous solution of rhamnolipid in the presence of ethanol on the polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) and quartz surface. The obtained results of the contact angle were analyzed in the light of the surface tension components of the solids, water, ethanol as well as the head and tail of the rhamnolipid surface tension. Based on these analyses the adsorption of the ethanol and rhamnolipid at the solid-solution, the dependence between adhesion and surface tension, the dependence between the adhesion work of the solution to the solid surfaces and solution surface tension as well as the critical surface tension of solid wetting were considered. The critical surface tension was compared to the surface tension of the solid. From above mentioned consideration, it appeared, among other things, that on the basis of the PTFE-aqueous solution of ethanol (ET) and PTFE-aqueous solution of rhamnolipid (RL) interface tension, it is possible to predict the contribution of ET and RL adsorption at the PTFE-solution of RL and ET mixture. It also appeared that it is possible to determine the Gibbs standard free energy of ET and RL adsorption at the solid-air and solid-solution interfaces, by using the Gibbs excess concentration of ET and RL at these interfaces determined on the basis of contact angle in Langmuir equation modified by de Boer. • Replacement of RL by ET molecules in interfaces layer can cause contact angle increase. • Above ET CAC contact angle depends practically on its adsorption at interfaces but not RL. • Parameter changes linearly as a function of logarithm from sum of and but not • Solution of ET and RL mixture spreads complete over PMMA and quartz at C of ET higher than its CAC. • For PMMA and quartz there is linear dependence between adhesion work and

Theory and simulation of shock waves: Entropy production and energy conversion.

We have considered a shock wave as a surface of discontinuity and computed the entropy production using nonequilibrium thermodynamics for surfaces. The results from this method, which we call the "Gibbs excess method" (GEM), were compared with results from three alternative methods, all based on the entropy balance in the shock-front region, but with different assumptions about local equilibrium. Nonequilibrium molecular dynamics (NEMD) simulations were used to simulate a thermal blast in a one-component gas consisting of particles interacting with the Lennard-Jones/spline potential. This provided data for the theoretical analysis. Two cases were studied, a weak shock with Mach number M≈2 and a strong shock with M≈6 and with a Prandtl number of the gas Pr≈1.4 in both cases. The four theoretical methods gave consistent results for the time-dependent surface excess entropy production for both Mach numbers. The internal energy was found to deviate only slightly from equilibrium values in the shock front. The pressure profile was found to be consistent with the Navier-Stokes equations. The entropy production in the weak and strong shocks were approximately proportional to the square of the Mach number and decayed with time at approximately the same relative rate. In both cases, some 97% of the total entropy production in the gas occurred in the shock wave. The GEM showed that most of the shock's kinetic energy was converted reversibly into enthalpy and entropy, and a small amount was dissipated as produced entropy. The shock waves traveled at almost constant speed, and we found that the overpressure determined from NEMD simulations agreed well with the Rankine-Hugoniot conditions for steady-state shocks.

Hydrogen-Enhanced Vacancy Diffusion in Metals.

Vacancy diffusion is fundamental to materials science. Hydrogen atoms bind strongly to vacancies and are often believed to retard vacancy diffusion. Here, we use a potential-of-mean-force method to study the diffusion of vacancies in Cu and Pd. We find H atoms, instead of dragging, enhance the diffusivity of vacancies due to a positive hydrogen Gibbs excess at the saddle-point: that is, the migration saddle attracts more H than the vacancy ground state, characterized by an activation excess ΓHm ≈ 1 H, together with also-positive migration activation volume Ωm and activation entropy Sm. Thus, according to the Gibbs adsorption isotherm generalized to the activation path, a higher μH significantly lowers the migration free-energy barrier. This is verified by ab initio grand canonical Monte Carlo simulations and direct molecular dynamics simulations. This trend is believed to be generic for migrating dislocations, grain boundaries, and so on that also have a higher capacity for attracting H atoms due to a positive activation volume at the migration saddles.

Comment on “Surface properties of ethanol/water mixture: Thickness and composition”

A controversial discussion regarding the estimation of surface thickness in aqueous ethanol as calculated by Phan and co-workers (2019) from neutron reflectivity experiments and by Bagheri et al. (2016) and Santos and Reis (2018) from surface tension data and equality of chemical potentials is addressed. The theoretical link among equilibrium mole fractions, Gibbs excess concentration, surface molar volume and interfacial thickness developed by Phan and co-workers is rearranged into an explicit expression for the calculation of thickness, which is shown to be inconsistent with their Gibbs excess concentration estimating equation from neutron reflectivity experiments. A correction is proposed, and the recalculated equivalent thickness values present an increase, with increasing ethanol contents, in fair agreement with the values reported by Santos and Reis (2018).

Surface properties of the ethanol/water mixture: Thickness and composition

Ethanol is a common amphiphilic solvent often used in conjunction with water. However, despite its widespread use, key questions regarding the thickness and composition of molecules at the ethanol/water/air surface remain unclear. Recent thermodynamic analyses, Bagheri and co-authors (2016) and Santos and Reis (2018), indicated that the interfacial thickness is not constant. However, the interfacial thickness from these two analyses follows opposite trends. This study aims to provide a detailed description of the thickness and composition of the interfacial layer by combining neutron reflectivity (NR) experiments with rigorous molecular simulation. The interfacial composition was determined from molecular simulations and, in conjunction with the Gibbs excess concentration, used to calculate the interfacial thickness. It was found that the thickness decreased exponentially and reached a plateau of ~ 8.2 Å. The results confirm the trends obtained thermodynamically from surface tension. The study also provides a new theoretical framework to describe the interfacial layer of water/alcohol mixtures.

Adsorption characteristics of supercritical CO2/CH4 on different types of coal and a machine learning approach

The injection of CO2 into deep coal beds can not only improve the recovery of CH4, but also contribute to the geological sequestration of CO2. The adsorption characteristics of coal determine the amount of the greenhouse gas that deep coal seams can store in place. Using self-developed adsorption facility of supercritical fluids, this paper studied the adsorption behavior of supercritical CO2 and CH4 on three types of coal (anthracite, bituminous coal A, bituminous coal B) under different temperatures of 35 °C, 45 °C and 55 °C. The influence of temperature, pressure, and coal rank on the Gibbs excess and absolute/real adsorption amount of supercritical CO2/CH4 on coal samples has been analyzed. Several traditional isotherm models are applied to interpret the experimental data and Langmuir related models are verified to provide good performances. However, these models are limited to isothermal conditions and are highly depended on extensive experiments. To overcome these deficiencies, one innovative adsorption model is proposed based on machine learning methods. This model is applied to the adsorption data of both this paper and four early publications. It was proved to be highly effective in predicting adsorption behavior of a certain type of coal. To further break the limit of coal type, the second optimization model is provided based on published data. Using the second model, one can predict the adsorption behavior of coal based on the fundamental physicochemical parameters of coal. Overall, working directly with the real data, the machine learning technique makes the unified adsorption model become possible, avoiding tedious theoretical assumptions, derivations and strong limitations of the traditional model.

Reanalysis of the Much Referenced Ethanol‐trichloromethane Mixture Vapor Pressure Data: A Discussion of the Principal Association Species Present

AbstractThe Scatchard (S) and Raymond (R) 1938 data on the vapor pressure above ethanol (1)‐trichloromethane (2) mixtures at the temperatures of 35, 45 and 55° C are still being used today in discussions of the thermodynamic properties and association species present in 1‐2 mixtures. Here a detailed reanalysis of the originally published SR data has been carried out using the model free Redlich‐Kister excess chemical potential approach as applied by Barker. These results show how small temperature variations drastically affect mixture vapor pressure measurements. A number of weaknesses in SR's original analysis of their data and significant discrepancies between R's thesis results and those in the published SR paper have been uncovered. These discrepancies would impact the conclusions of anyone using SR's results. From the present reanalysis more accurate temperatures dependent Gibbs excess energies, excess entropies, excess enthalpies and activity coefficients have been calculated that could not been obtained from SR data analysis scheme. Based on available experimental and theoretical studies of the 1‐2 system it is argued that the major association species should be the cyclic 111 trimer and that the dimer 22 should be considered. This is counter to a current model for this system.

Electrical double layer and adsorption of iodide ions at the Bi|ethylene carbonate interface

The adsorption of I− anions on the Bi(111) single-crystal plane from solutions in ethylene carbonate has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained by integration of differential capacitance curves, and the Gibbs excess has been calculated using the mixed-electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of I− anion adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions, the results obtained at constant electrode potential and at constant electrode charge were coincident. The Gibbs energy of I− anion adsorption and the calculated electrosorption valency value were found to be very close to these values obtained in propylene carbonate.

Coalbed methane adsorption behavior and its energy variation features under supercritical pressure and temperature conditions

A majority of coalbed methane (CBM) in coal reservoirs is in an adsorbed state. Under geological pressure and temperature conditions (beyond the critical region of methane), supercritical adsorption occurs between methane (CH4) molecules and coal surface. In order to better characterize CBM supercritical adsorption behaviors, isothermal adsorption tests were conducted to simulate the adsorption under different reservoir pressures and temperatures. It is observed that the temperature influences adsorption behaviors little under low-pressure conditions but weakens the sorption capacity of coals under high-pressure conditions. Since the adsorption volume obtained from isothermal adsorption tests is Gibbs excess adsorption volume, it was transformed to the absolute adsorption volume which is essential for reliable gas-in-place estimates. A hypothesis was proposed that a maximum adsorption volume for a certain adsorbent exist in the limiting case of supercritical conditions. Based on this, the limiting adsorption model was built in reference to the Dubinin-Astakhov (DA) adsorption model and Henry dissolution law. Additionally, different energy varying trends (adsorption potential, adsorption space, reduction of surface free energy and isosteric heat of adsorption) over pressure and temperature indicate that the adsorption of CH4 by coals is actually the attraction between CH4 molecules and coal molecules and also a spontaneous process to reduce surface free energy of the system. The pressure and temperature exert an impact on sorption behaviors by controlling attraction forces or kinetic energy of adsorbate and adsorbent molecules.

Calculating the excess gibbs energy of real ternary solutions on the basis of the non-random two-liquid model

The concentration dependences of the excess Gibbs energy of ternary solutions with various deviations from ideality are calculated on the basis of the non-random two-liquid (NRTL) model.

Thermodynamic studies of anion adsorption at the Pt(111) electrode surface from glycolic acid solutions

Kinetic glycolic acid (GA) oxidation and thermodynamic glycolate adsorption have been studied on Pt single crystal electrodes. The voltammetric profiles of Pt(111), Pt(100), and Pt(110) in 0.1 M GA are shown, and the effect of the inclusion of steps on the Pt(111) surface has been studied by cyclic voltammetry. For Pt(111) electrode, different concentrations and sweep rates have been applied, revealing that both adsorption and oxidation processes take place. By establishing the appropriate conditions, a complete thermodynamic analysis has been performed by using the electrode potential and the charge as independent variables. Total charge density curves, surface pressure at total charge density and at constant electrode potential were determined to calculate the Gibbs excess and the charge number at constant electrode potential for glycolate adsorption on Pt(111). Maximum glycolate coverage on the surface reaches a value of ∼6.0 × 1014 ions/cm2. Spectroscopic results show the formation of CO2 during the oxidation of glycolic acid, indicating that the cleavage of the C–C bond occurs during the oxidation process.

Calorimetric investigation of Al–Zn alloys using Oelsen method

The results of calorimetric study of binary Al–Zn system done according to the Oelsen thermodynamic method are presented in this paper. Main thermodynamic properties, including activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies were determined at 1,000 K. Positive deviation from Raoult law was noticed, with minimal values of ΔG M about −3 kJ mol−1 and maximal values of ΔG E about +2 kJ mol−1. The energetics of mixing in liquid Al–Zn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit, and weak affinity between Al and Zn atoms in the system was observed. Differential thermal analysis and light optic microscopy were applied in the frame of characterization of investigated binary alloys and phase diagram examination, and the results obtained were in accordance with available literature data.

Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius–Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius–Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius–Clapeyron and Clapeyron equations from hydrogen sorption data for two materials—activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius–Clapeyron equation can only be used at low coverage, since hydrogen’s behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius–Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters.

High pressure solubility of CO2 in non-fluorinated phosphonium-based ionic liquids

High pressure solubility of carbon dioxide in three phosphonium-based ionic liquids has been measured experimentally. A synthetic method was used to measure vapor–liquid, vapor–liquid–liquid and liquid–liquid equilibria of carbon dioxide in the ionic liquids trihexyltetradecylphosphonium bromide [thtdp][Br], trihexyltetradecylphosphonium dicyanamide [thtdp][dca] and trihexyltetradecylphosphonium bis(2,4,4-trime-thylpentyl)phosphinate [thtdp][phos] for a temperature range of 271–363K and up to 90MPa. Furthermore, the densities and viscosities of these ILs have been measured in a temperature range of 293–363K. The solubility of carbon dioxide in these ILs is (on mole fraction basis) significantly larger than most of the commonly used fluorinated imidazolium ionic liquids. The latter statement, however, does not hold for the [Br] and [dca] based IL if the solubility is compared on molality (mole/mass solvent) basis, where the solubility differences among physical ILs tends to vanish indicating a strong molecular weight effect. The solubility of carbon dioxide in [thtdp][phos], both on mole fraction and molality basis, is among the highest compared to all the other physical ILs reported so far in the literature. The Peng–Robinson equation of state in combination with Wong–Sandler mixing rules incorporating the NRTL Gibbs excess energy model was applied to represent the experimental data with acceptable accuracy.

Comparative thermodynamic analysis and phase diagram prediction of the Ga – Sn – Zn system

AbstractThe results of comparative thermodynamic analysis and phase diagram prediction of the Ga – Sn – Zn system are presented in this work. The thermodynamic study was done experimentally – using Oelsen calorimetry, for the section Ga – SnZneut, and analytically – according to the general solution model, for the whole system. Main thermodynamic quantities – integral and partial molar Gibbs excess energies, activities and activity coefficients were calculated over a wide temperature range. Additionally, the phase diagram of the section Ga – SnZneut was investigated using differential thermal analysis and predicted using the CALPHAD method. Comparison with available literature data showed reasonable agreement. The liquidus projection of the ternary Ga – Sn – Zn was also calculated.

Comparative analyses of thermodynamic properties assessments, performed by geometric models: Application to the Ni-Bi-Zn system

The thermochemical properties of metals and alloys are essential for the chemists to invent and improve metallurgical and materials? design processes. However, the properties of multicomponent systems are still scarcely known due to experimental difficulties and the large number of related systems. Thus, the modelling of some thermodynamic properties would be advantageous when experimental data are missing. Considering mentioned facts, geometric models to estimate some thermodynamic properties for the liquid phase of the Ni-Bi-Zn systems. The calculations have been performed in a wide temperature range (1000-2000 K). Ternary interaction parameters for the liquid phase allowing molar Gibbs excess energy calculation have been determined.

Crystallographic dependence of 4-dimethylaminopyridine electrosorption on gold

Using differential capacity we have compared the electrosorption of dimethylaminopyridine (DMAP) on Au(poly), Au(100), and Au(111) electrode surfaces. Thermodynamic analyses of charge density data have provided quantitative information concerning the Gibbs excess of the films and the bonding motif between the adsorbate and the Au(111) surface. The results indicate that the orientation of DMAP is highly dependent on electrode potential, electrolyte pH, and surface crystallography. At pH equal to the pKa of the conjugate acid, the dominant adsorbed species is the free base, DMAP, but its adsorption state depends on the electrical state of the Au(111) surface. Negative polarizations favor a low coverage state with individual DMAP molecules coordinated through both the aromatic ring and the exocyclic tertiary amine. Positive polarizations induce a phase transition that provides a high density monolayer of DMAP coordinated to the Au(111) surface through the lone pair of the endocyclic nitrogen. The phase transition at high pH is unique to Au(111) as Au(100) and Au(poly) has been shown to only exhibit the high density state of adsorption. In slightly acidic electrolytes the adsorbed species on Au(111) and Au(100) is the protonated ion, DMAPH+, and no phase transitions were observed. The data provide the basis from which a rational strategy for synthesizing anisotropic gold nanocrystals can be developed.

A self-consistent Gibbs excess mixing rule for cubic equations of state

The extension of the applicability of cubic equations of state (EoS) with Gibbs excess models to the prediction of high-pressure/high-temperature vapor–liquid equilibria of polar and/or asymmetric is well known. Despite the success of this category of mixing rules (EoS/GE), the combined model is often less accurate than the Gibbs excess model alone at low pressure. In this work a new Gibbs excess mixing rule for cubic equations of state is developed. The proposed method was derived solely based on the assumption of a zero excess volume liquid-like phase. Tests with substances dissimilar in size, shape and chemical nature have shown that any cubic equation of state coupled with the proposed mixing rule can reproduce the underlying liquid activity model at low pressures, showing that the method is self-consistent. Further, the method was extended for high pressures/temperatures by assuming a constant thermal expansion coefficient liquid-like phase as the reference state. Very good results were obtained when the proposed method was coupled with Wilson, UNIQUAC, UNIFAC and a COSMO-based model in liquid–liquid and vapor–liquid equilibrium examples.

Calorimetric study and thermal analysis of Al–Sn system

The results of calorimetric study and thermal analysis of binary Al–Sn system are presented in this paper. The Oelsen calorimetry was used in thermodynamic analysis. Following thermodynamic properties were determined at 727 °C: activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies. The energetics of mixing in liquid Al–Sn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit. Thermal analysis of selected alloys in Al–Sn system was done using differential thermal analysis. Defined characteristic phase transition temperatures were used for comparison with calculated phase diagram of investigated system. Good agreement with available literature data was obtained. Structural analysis of selected alloys was done using optic microscopy.

A revisit to the Gibbs dividing surfaces and helium adsorption

This paper addresses the long-standing problem of the so-called Gibbs dividing surface and the use of helium as a “non-adsorbing” gas for the determination of the “helium”-void volume and thence the Gibbs excess. Using helium is subject to some uncertainty because helium does adsorb (to call it a non-adsorbing gas is misleading) and it is able to access pore spaces that other larger adsorbates cannot. On the other hand, even helium atoms can not physically probe all the space described by the helium-void volume. To avoid these difficulties, we suggest an alternative to the formulation of the Gibbs dividing surface and the definition of the excess amount. We illustrate this with the two common tools to study adsorption—the volumetric and gravimetric techniques, and justify our new analysis with a computer simulation of a number of model adsorption systems. Furthermore, we also show that by using the correct accessible volume and inaccessible volume the excess amount obtained from a volumetric experiment is exactly the same as that obtained from a gravimetric experiment.