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In the present study, we have reported a detailed assessment of interactional behavior between the surface active ionic liquid (SAIL) lauryl isoquinolinium bromide ([C12iQuin][Br]) and anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-MA) in aqueous media. Various techniques such as surface tension, conductance, dynamic light scattering, and turbidity have been employed to get insight into interactions among [C12iQuin][Br] and polyelectrolyte in the interfacial region. Then, surface parameters such as surface excess concentration (Γcmc), surface pressure at interface (Πcmc), minimum area occupied by one molecule of SAIL at air–solvent interface (Αmin), adsorption efficiency (pC20), and surface tension at critical micelle concentration (cmc) (γcmc) have been calculated from tensiometric measurements. Further, thermodynamic parameters, i.e., standard enthalpy of micellization $$ \left(\Delta {H}_{\mathrm{m}}^{{}^{\circ}}\right) $$ , standard free energy of micellization ( $$ \Delta {G}_{\mathrm{m}}^{{}^{\circ}} $$ ), and standard entropy of micellization ( $$ \Delta {S}_{\mathrm{m}}^{{}^{\circ}} $$ ) have been evaluated. The size and shape of complexes formed among [C12iQuin][Br] and polyelectrolyte have been characterized using DLS and turbidity measurements.

We have investigated the surface activity of poly(ethylene glycol) (PEG)-coated silver nanoparticles (Ag-PEG) in the presence or absence of lipid monolayers comprised of monounsaturated dioleoylphosphocholine and dioleoylphosphoglycerol (DOPC/DOPG; 1:1 mol ratio). Dynamic measurements of surface pressure demonstrated that Ag-PEG were surface-active at the air/water interface. Surface excess concentrations suggested that at high Ag-PEG subphase concentrations, Ag-PEG assembled as densely packed monolayers in the presence and absence of a lipid monolayer. The presence of a lipid monolayer led to only a slight decrease in the excess surface concentration of Ag-PEG. Surface pressure–area isotherms showed that in the absence of lipids Ag-PEG increased the surface pressure up to 45 mN m–1 upon compression before the Ag-PEG surface layer collapsed. Our results suggest that surface activity of Ag-PEG was due to hydrophobic interactions imparted by a combination of the amphiphilic polymer coating and the hydrophob...

Herein, with the aim of shedding light on the effect of non-ionic co-solute (carbohydrate) stereochemistry on the aggregation and surface behaviour of ionic liquid-based surfactant 1-decyl-3-methylimidazolium bromide ([C 10 mim][Br]) in aqueous solution, we studied the surface tension, electrical conductivity, volumetric and compressibility properties for the aqueous solutions of [C 10 mim][Br] in the presence of different sugars containing pentose monosaccharides (xylose, ribose and arabinose), hexose monosaccharides (glucose, and mannose), disaccharides (sucrose and lactose) and trisaccharide (raffinose) at different temperatures. From the electrical conductivity measurements, the values of the degree of ionization of the counter ion on the micelles (α) and thermodynamic properties of micellization (Δ G m ) for [C 10 mim][Br] in aqueous carbohydrate solutions were obtained. The various parameters such as apparent molar volume ( V ϕ ), isentropic compressibility (κ s ), apparent molar isentropic compressibility ( K ϕ ) and the change of apparent molar properties upon micellization (Δ V ϕ,m and Δ K ϕ,m ) were derived from the experimental density and speed of sound data. The surface tension measurements provided a series of parameters, including surface tension at the cmc ( γ cmc ), effectiveness of surface tension reduction ( Π cmc ), maximum surface excess concentration ( Γ max ) and minimum surface area per molecule ( A min ) at interface of air/solution for the investigated surfactant in the presence of different sugars at 298.15 K. All the investigated carbohydrates have soluting-out effect (favouring the micelle formation) and their abilities to reduce the cmc of [C 10 mim][Br] in aqueous solutions increase with an increase in the hydrophilicity of the carbohydrate.

The influence of the long chain ionic liquid 1-hexadecyl-3-methyl imidazolium chloride on equilibrium and dynamic interfacial tensions of n -heptane/water, as a representative system of oil/water, was investigated. Interfacial tension was drastically decreased by the ionic liquid and presence of magnetite nanoparticles as low as 0.01 wt%. Alkaline pH intensifies this effect. It was while nanoparticles alone had no sensible effect. The equilibrium interfacial tension data were nicely reproduced by the Szyszkowski model. Accordingly, the saturated surface excess for the systems with nanoparticles was decreased compared to the particles free case, but the adsorption equilibrium constant was increased. The dynamic interfacial tension data, on the other hand, showed a good agreement with the mixed diffusion-kinetic control theory for the both cases. Further, the stability of different emulsions was investigated. The results showed that the used nanoparticles were poor emulsifying agent, but the emulsion stability was increased when accompanied with the ionic liquid. Finally, the contact angle of aqueous phase drops surrounded by n -heptane on quartz surface was consistently decreased with the ionic liquid concentration and was more in the presence of nanoparticles.

Adsorption methods for determining the properties of stainless steel surface are presented. The relation between the actual and geometric surface is determined. The dependence of adsorption heat on the coverage logarithm is derived from experimental adsorption isotherms for water at 298 K. On the basis of this dependence, differential and integral distribution functions of adsorption sites by adsorption heat is calculated. It is shown that in the case of water adsorption on the surface of stainless steel at 298 K, adsorption heat for 90% of adsorption sites ranges from 4.4 × 107 to 7.9 × 107 J/kmol.

The influence of halide ions of (sodium salt) electrolytes on the mixed micellization of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium) bromide (16-6-16) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB) have been investigated. The critical micelle concentration (CMC) of the mixed (16-6-16+CTAB) surfactants was measured by the surface tension measurements. The surface properties: viz., the surfactant concentration required to reduce the surface tension by 20 mN/m (C20), the surface pressure at the CMC (ΠCMC), the maximum surface excess concentration at the air/water interface (Γmax), the minimum area per surfactant molecule at the air/water interface (Amin), etc. of the mixed micellar surfactant systems were evaluated. In the absence and presence of electrolytes, the thermodynamic parameters of the mixed micellar surfactant systems were also evaluated.

In most of existing works on the instabilities of an evaporating film, the energy boundary condition only takes into account contributions of the evaporation latent heat and the heat conduction in the liquid. We use a new generalized energy boundary condition at the evaporating liquid-vapor interface, in which the contribution of the transport of the Gibbs excess energy is included. We have derived the long-wave equations in which the thickness of film and the interfacial temperature are coupled to describe the dynamics of an evaporating thin film. The results of our computation show that the transport of the Gibbs excess internal energy delay the rupture of thin films due to van de Waals force, evaporating effect and vapor recoil.

A very low interfacial tension, γ, can be achieved between an oil phase and an aqueous solution containing anionic surfactant and salt at a very low concentration. This phenomenon can have potential applications in recovering residual oil from the reservoir through low salinity–low surfactant enhanced oil recovery flooding. Measurements of γ between n-heptane and aqueous solution of anionic surfactants in the concentration range of 0.141–2.167 mM and salts in the concentration range of 9.010–119.780 mM at 313.15 ± 0.1 K have been carried out. The experimental results show that the value of γ falls to a lowest value at a temperature above the Krafft point when the concentration of anionic surfactants [sodium dodecyl sulfate (SDS) and dioctyl sulfosuccinate sodium salt (AOT)] is increased up to a maximum surface excess concentration in an aqueous solution in the presence of monovalent [sodium chloride, (NaCl)] and divalent [calcium chloride, (CaCl2)] salts in the low concentration range. To understand and a...

In this way, after experimental measurement of interfacial tension, different models including mono-exponential decay, dynamic adsorption models and empirical equation are used to correlate this time-dependent behavior of interfacial tension (IFT). During the modeling approach, the induction, adsorption, equilibrium, and meso-equilibrium times as well as diffusivity of surface active components known as natural surfactant including asphaltene and resin from crude oil to the interface are obtained. In addition, the surface excess concentration of surface active components at the interface and Gibbs adsorption isotherm are utilized to analyze the measured dynamic IFTs. Finally, the mechanisms of crude oil/aqueous solution IFT including (a) the activity of surface-active components and (b) surface excess concentration of them at fluid/fluid interface are proposed and discussed in details.

Batch experimental studies were carried out on the adsorption of 13-dehydroxybaccatin III (13-DHB III) using Sylopute while varying parameters such as initial 13-DHB III concentrations, contact times and adsorption temperatures. Out of Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models, adsorption data with the highest accuracy were best described by the Langmuir isotherm. It was found that the adsorption capacity decreased with an increasing temperature and the adsorption of 13-DHB III onto Sylopute was favourable. The adsorption kinetics were well described by the pseudo-second-order kinetic model, while intraparticle diffusion and boundary layer diffusion did not play a dominant role in 13-DHB III adsorption according to the intraparticle diffusion model. Thermodynamic parameters revealed the exothermic, irreversible and non-spontaneous nature of adsorption. The isosteric heat of adsorption was constant even with variations in surface loading, indicating a heterogeneous surface.

The main aim of this work is to study the interface of dimethylsulfoxide + n -alkanol mixtures. To achieve this aim, first, the surface tension of (dimethylsulfoxide + methanol, ethanol, and propanol) was measured as a function of mole fraction and temperature. These measurements were conducted in the temperature range of (293.15–308.15) K and atmospheric pressure. Then the surface tensions of binary mixtures were correlated by Shereshefsky model and excellent results were obtained. The average percent deviation in correlation of surface tension of studied mixtures was 0.7%. Based on Shereshefsky model, the standard Gibbs energy of adsorption and the free energy change in the surface region were calculated. The free energy change was used to obtain the excess number of molecular layers in the surface region. Additionally, the extended Langmuir model was applied. The required parameters of the model were adjusted, the standard Gibbs energy of adsorption was calculated, and positive or negative deviations from ideality were determined. Also surface compositions were calculated by using extended Langmuir model. In addition to these two methods, a predictive model based on the equality of the chemical potential of species in the interface and bulk liquid was used to predict surface compositions and surface tension of mixtures. Additionally, by using surface tensions of studied mixtures at different temperaturs, specific surface enthalpy and specific surface entropy were calculated for (dimethylsulfoxide + n -alkanol) mixtures.

The measurements of the contact angle of aqueous solution of ethanol and surfactin mixture in the whole range of ethanol concentration on PTFE, PMMA and quartz were made at changing ethanol concentration and constant of surfactin and vice versa. Based on the obtained results, the Young-Dupre and van Oss et al. equations, the intermolecular interactions parameter between the solution and solid phases was determined and used to explain the possibility to form the ethanol and surfactin mixed layer beyond the solution drop settled on the PMMA and/or quartz surface. This layer pressure and that at the PMMA-solution, the quartz-solution interface was determined using the Young-Dupre and van Oss et al. equations and applied for the ethanol and surfactin Frumkin isotherm adsorption determination. The Gibbs adsorption isotherm was also determined. The ethanol and surfactin Gibbs and Frumkin isotherms at the solid-solution, solid-air interfaces were compared to those at the solution-air one. From these isotherms of surfactin and ethanol adsorption at three interfaces, the slope of the linear dependence between the adhesion and surface tension was explained. The Gibbs isotherm was applied for determination of the Gibbs standard free energy of ethanol and surfactin adsorption at the solid-air and solid-water interfaces.

The surface excess isotherms of methanol from carbon dioxide on reversed phase stationary phases under two different operational conditions – which can be considered subcritical and supercritical conditions depending on the molar fraction of CO2 in methanol – were determined using the minor disturbance peak method. The shapes of the surface excess isotherms were very similar in subcritical and supercritical conditions for the same column. To verify the influence of the sample solvent on the separation efficiency, two solvents methanol and heptane were used as sample solvents for alkylbenzene samples for the separation on the studied columns with pure carbon dioxide mobile phase. The separation efficiency was determined by calculating the number of theoretical plates. On the embedded amide stationary phase with methanol as a sample solvent the efficiency has increased due to the displacement effect of methanol on the solutes which are retained less than methanol. Then the efficiency for the rest of solutes, which coincide with the elution of the methanol peak tail has decreased as a result of the tag-along effect. The surface adsorbent heterogeneity has been discussed; the bonded ligands on the stationary phase surface demonstrated adsorption a big amount of CO2, while methanol could adsorb with small amount on the residual silanols on the surface of stationary phase and the embedded (amide) polar group in the bonded phase.

Salt free surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium dodecyl sulfate ([bmim]DS) and N-butyl-N-methylpyrrolidinium dodecyl sulfate ([bmp]DS) were synthesised by stoichiometric mixing of ionic liquid (IL) and sodium dodecyl sulfate (SDS). SAILs were characterised by FTIR, 1H NMR, 13C NMR and thermogravimetric analysis and differential thermal analysis (TGA-DTA). Interfacial and aggregation behavior of the SAILs were investigated by surface tension, conductance, UV–visible absorption, emission spectroscopy, dynamic light scattering and isothermal titration calorimetric studies. Results were compared with the precursor surfactant SDS. Critical micelle concentration (CMC) of the surfactants followed the sequence: SDS > [bmp]DS > [bmim]DS. Lower surface excess values of SAILs were due to electrostatic interaction between IL cation and DS-, besides the higher aqueous solubility of DS-, induced by the IL cations. Negative Gibbs free energy of micellization and higher fraction of counter ion binding values further support the proposition. Aggregation number (n) and size (dh) of the micelles were determined by fluorescence quenching and dynamic light scattering studies respectively; both ‘n’ and ‘dh’ values were higher for SAILs than SDS ([bmim]DS > [bmp]DS > SDS). SAIL aggregates, although larger in size with higher aggregation number, were more compact than SDS micelles. Enthalpies of micellization, being exothermic in nature, were higher for SAILs although the micellization processes were entropically controlled. SAILs are considered to have dual advantages of surfactant and IL with substantial decrease in toxicity level.

Adsorption kinetics of industrially relevant emulsifiers typically show complex behaviour that cannot be simply explained by conventional adsorption kinetics models. In this work, we seek to understand the complex adsorption behaviour of PiBSA (polyisobutenyl succinic anhydride) based emulsifiers and SMO (sorbitan monooleate), which have significant industry relevance as they are often used as the stabiliser in emulsion explosive formulations. We attempt to explain the dynamics of multiple adsorbing species in emulsion systems by using PiBSA based emulsifiers and SMO as a model. We measure dynamic interfacial tension at toluene–water and methylated canola oil (mc oil)–water interfaces using pendant drop tensiometry for different concentrations of four industrial-grade emulsifiers that have different head group chemistries. Using our experimental measurements of dynamic interfacial tension, we estimate the dynamic adsorbed amounts of these emulsifiers using the Gibbs isotherm and Langmuir-Szyszkowski equation. The observed adsorption kinetics of these emulsifier molecules deviate from a single-mode adsorption process, likely because of competition between the kinetically versus thermodynamically favoured molecules present in the emulsifier, and the total dynamic adsorbed amount thus depends on the competition between these faster-diffusing (kinetic) and slower-diffusing (thermodynamic) species. We demonstrate that the adsorption kinetics of all the four types of emulsifiers near their equilibrium adsorption states can be well approximated by the ‘two adsorbing species model’ discussed in our previous work (Tripathi and Tabor, 2016).

The micellization behaviour of biamphiphilic surface active ionic liquid (BAIL), 3-methyl-1-pentylimidazolium dodecylsulfate [C5mim][C12SO4] with anionic surfactant, sodium dioctylsulfosuccinate (AOT) was investigated using different techniques in an aqueous solution. The values of critical micelle concentration (cmc) and thermodynamic parameters have been ascertained by employing conductometric measurement at (298.15, 308.15 and 318.15) K. The interfacial parameters viz. surface pressure, maximum surface excess concentration, and minimum surface area per surfactant molecule evaluated by using the surface tension measurement at 298.15 K shows the less effectiveness of mixtures to reduce the surface tension. The size and turbidity of the mixed aggregates were investigated using dynamic light scattering (DLS) and turbidimetry. The turbidity results show the existence of micelles as well as mixed aggregates. Different proposed theoretical models like Clint, Rubingh and Motomura was employed for the evaluation of mixed micellar parameters (ideal values of cmc, activity coefficients of the components in the mixed micelle, and interaction parameters etc.) at different compositions. The existence of both the interactions (synergistic and antagonistic) has been inferred in the studied system. The mixed micelle formation was found dependent on micellar composition.

The theoretical principle of choosing suitable room temperature ionic liquids (RTILs) for liquid phase exfoliation of graphene sheet remains a challenge. A simple thermodynamic model is proposed to show the vital role of the solvation energy as an indication of solvent quality for spontaneous exfoliation. The solvation energy of ten ILs surrounding a single graphene sheet has been determined by molecular dynamics (MD) simulations. It is found to be strongly correlated with surface excess, sheet deformation and surface tension. From the MD simulations [BMIM][TF2N] (-580.86 mJ.m−2), [BPY][ TF2N] (-565.19 mJ.m−2) and [BMP][TF2N] (-551.77 mJ.m−2) shows stronger affinity with graphene surfaces as compared to other ILs. On the basis of the established mechanism, one is able to predict and screen suitable IL for spontaneous exfoliation of graphene.

In this work, an alternative physicochemical procedure is presented to characterize the liquid-vapor interface of binary liquid mixtures containing non-ionic surfactants, using the Gibbs adsorption isotherm, the solute activity, and the surface partial molar areas. This model allowed to calculate the moles of solute and solvent present in equilibrium for both bulk and surface phase. The excess surface concentration, relative surface concentration, and molar fraction of both components was also calculated. The results reflected that the excess surface concentration of the solute was not proportional to the adsorption of the solute with the increase in its concentration in the bulky phase. This gives evidence that the dilute solutions were able to saturate the surface layer at an early stage and after it, for the entire concentration range where it remains approximately constant, which showed the existence of a compact molecular arrangement.

In this study, the removal of cobalt from an effluent was investigated probably for the first time by foam fractionation. Foam fractionation is considered as a green method because of its friendly nature, high removal efficiency, costs effectiveness and non-hazardous nature. Sodium dodecyl sulfate (SDS) was used as an anionic surface-active agent and the effect of gas flow rate, the initial concentrations of surfactant and cobalt and pH on the cobalt removal efficiency was investigated. The results showed that by increasing surfactant concentration and gas flow rate, the cobalt removal efficiency would be improved however, the cobalt concentration in foamate would decrease at high gas flow rates. High gas flow rates generally produce dilute foamate. Drainage of the interstitial bulk fluid that is entrapped between the foam bubbles has a key importance in the normal performance of the foam fractionation operation. Experiments showed that the well-drained foams are low in volume and high in Co2+ leading to an easier separation of their ingredients that usually follows. The efficiency reached the highest when cobalt feed concentration was about 1 mg/L, but dropped gradually in higher concentrations. By increasing pH to around 5, high removal efficiency was achieved and then decreased again. The optimum conditions for high cobalt removal efficiency were obtained when SDS concentration was about 100 mg/L and the initial cobalt concentration was below and close to 1 mg/L. The results of experiments revealed that the amount of cobalt removed per unit weight of SDS was higher for low [SDS]/[Co2+] ratios. They also showed that the air–liquid interface coverage by surface excess solute ions would not be more that 5% of the total area. Under optimum conditions for cobalt removal pH value and gas flow rate were found to be around 5 and 9 L/h, respectively. Under these conditions the removal efficiency was shown to be 99.4%.

The application of nanoparticles (NPs) in many fields generated large amounts of wastewater which would result in resource loss and environmental pollution. In this work, foam fractionation was used to recycle NPs from their aqueous suspensions and a novel method was developed to strengthen foam drainage through regulating bubble size distribution. The results showed that the adjacent bubbles with different size were easy to coalesce and then the bubble size and surface excess were enhanced simultaneously. Thereby strengthening foam drainage and foam stability simultaneously. The enrichment ratio of NPs increased approximately 45% with almost no loss of recovery percentage by using this method. The recycle efficiency of NPs was also affected by their structures and shapes that the recycle of tubular NPs was more efficient than globular NPs. Under the suitable conditions, the enrichment ratio and recovery percentage of silica nanoparticles (SNPs) and carbon nanotubes (CNTs) were 7.1, 90.1% and 9.9, 94.5%, respectively.

The traditional adsorbents for antimonate (Sb(V)) in industrial effluent suffered from poor adsorption capacity due to the lack of pores or adsorption sites. Three-dimensional (3D) amidoxime-polyacrylonitrile sphere (APANS) with hierarchical pores and abundant amidoxime groups was fabricated via nanoscale thermally induced phase separation (TIPS). The effects of fabrication parameters including diluent type, PAN concentration and amidoximation time on pore structure were studied with scanning electron microscopy (SEM), mercury intrusion instrument (MIP), fourier transform infrared spectrophotometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). Results showed that APANS fabricated from 2% PAN/DMSO solution and amidoximated for 20 min had coarse surface, numerous mesopores, high porosity (88.5%) and large pore volume (20.5 mL/g). The pore formation mechanism revealed that the hierarchical pores were derived from multiscale DMSO crystals shaped by TIPS. Adsorption kinetics results showed that kinetics data were well fitted by pseudo-second-order model (R2 > 0.99) and the mesopores accelerated the adsorption (equilibrium time of 4 h) due to enormous surface excess and group exposure. Adsorption isotherm could be modeled by Freundlich (R2 > 0.99) and maximum adsorption capacity was 683.6 mg/g. The adsorption thermodynamics was also investigated, indicating the spontaneous and exothermic adsorption process. APANS exhibited excellent selectivity towards common anions (Cl−, SO42−, NO3− and PO43−) and reliable reusability (preserving 80% capacity after five cycles). This adsorbent provided a clean and sustainable strategy for Sb(V) removal from aqueous environment by superhigh capacity, fast rate and reliable reusability.

The aggregation behavior of three AOT based ionic liquids have been investigated in aqueous medium in the presence of different concentrations i.e. (0.04, 0.08, 0.12, 0.16) mM of sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) at different temperatures (298.15, 308.15, 318.15) K. The AOT based ionic liquids have been successfully synthesized by replacing the cation of sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) with various pharmacologically active cations such as cholinium [Cho]+, tetraethylammonium [TEA]+, and tetrabutylammonium [TBA]+. The conductivity and surface tension measurements have been employed to understand their aggregation behavior by evaluating various thermodynamic and surface-active parameters such as standard free energy of micellization ( Δ G m 0 ), standard enthalpy of micellization ( Δ H m 0 ), standard entropy of micellization ( Δ S m 0 ), surface pressure at cmc ( a ¨ cmc ) , maximum surface excess concentration ( Γ max ), the minimum area of surfactant monomer at the air/water interface ( A min ), the standard Gibbs free energy of adsorption ( Δ G ad 0 ) and the free energy of a surface at equilibrium ( G min s ).

The interfacial and micellization behavior of binary mixture of an amino sulfonate amphoteric 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) and a cationic octadecyltrimethyl ammonium bromide (OTAB) were investigated in aqueous solution without or with a 70 g/L alcohol (including methanol, ethanol, 1-propanol and 1-butanol) at 313.15 K by both the tensiometry and the conductometry. The surface excess concentration, the minimum area per surfactant molecule at the saturated interface and the standard free energy of adsorption at the air-liquid interface were adopted to be characteristic of the interfacial adsorption monolayer. Based on the pseudophase separation model and the regular solution theory, the Clint’s model and the Rubingh’s model was used to obtain the related parameters including the interaction parameters between two surfactant molecules, the compositions and the activity coefficients in mixed micelle and thermodynamic parameters. The effect of the alcohol chain length on the interfacial adsorption and the mixed micellization was discussed. The addition of short chain alcohol influences the properties of mixed cosolvent, the conformation of C12AS molecule and the electrostatic interaction between two surfactant molecules. Thermodynamic data shows that the presence of alcohol with a longer chain is beneficial to form the adsorption monolayer and the mixed micelle, and also it depresses the contribution of entropy to the process of micellization. These findings help with understanding the mechanism on the effect of short chain alcohol on the interfacial and micellization behavior of binary surfactant mixtures and further designing the surfactant formulations.

This paper presents a brief description of the role of interfacial energies in the understanding and control of nanocrystalline complex oxides in both particulate and bulk forms. Interfacial energies are fundamental parameters in microstructural evolution processes such as phase transformation, grain growth, and sintering. Although generally considered constant driving forces, experimental evidences confirm the possibility of intentional modification of both surface and grain boundary energies in oxide systems via ionic doping. This opened the perspective for a systematic understanding of their roles as refining parameters in microstructural control during processing and in operation. In this work, the theoretical framework in the context of Gibbs adsorption isotherm and the formation of dopant excess (i.e. interfacial solute segregation) is introduced in a similar manner as formalized for liquid systems. A collection of data demonstrating interfacial energy control in oxides is presented and discussed in terms of microstructural relationships with specific examples. The data advocates for a paradigm shift on nanocrystalline processing control from a traditionally kinetically oriented perspective to a more balanced viewpoint in which thermodynamics can play a governing role, especially at moderate temperatures. The work is not an extensive review, but rather has the goal of introducing the reader to this growing research topic.

The interfacial properties of crude oil are highly complex and are not yet well understood. This study aimed to evaluate the effect of temperature (30–80 °C) and pressure (3.44–27.58 MPa) on the dynamic interfacial tension (IFT) of crude oil/aqueous solutions consisting of 15 000 ppm of salt containing different chloride anions, e.g. NaCl, KCl, MgCl2, and CaCl2. To reach this goal, several parameters such as dynamic and equilibrium IFT, adsorption time, diffusivity of resin, and asphaltene as surface-active agents from bulk of crude oil towards fluid/fluid interface and surface excess concentration of them at the interface were compared as a function of temperature, pressure, and ion type. The obtained results clarified the reason why there are contradicting observations in the literature on the influence of temperature on the equilibrium IFT of crude oil/brine solutions. This article is protected by copyright. All rights reserved

This work is to answer an important question: which parameter, surface concentration or surface excess, dominates the surface tension of multicomponent mixtures? Two series of solutions have been chosen to inspect the dependence of solution surface tension on surface concentration and surface excess of the solutes. The solutions are separately 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in 3-hydroxypropionitrile and tetrabutylphosphonium bromide (TBPBr) in formamide. The surface tension data of these two series of binary solutions have been respectively correlated to the Gibbs surface excess and the surface concentration of the solutes. Both surface excess and surface concentration are experimentally determined by Neutral Impact Ion Scattering Spectroscopy (NICISS). The surface tension of POPC solutions is linearly dependent on the surface concentrations of POPC; whereas, the surface tension of TBPBr solutions depends piecewise linearly on surface concentration but irregularly upon surface excess of TBPBr. The intrinsic linear relationships between surface tension and surface concentration found in those two series of solutions are consistent to those results found in previous work. This observation evidences that the dominant factor to the surface tension of solutions is the surface concentration of solute to which both the surface fraction and the molecular orientation are subject.

The surface tension of the air-water interface increases upon the addition of inorganic salts, implying a negative surface excess of ionic species. Most acids, however, induce a decrease in surface tension, indicating a positive surface excess of hydrated protons. In combination with the apparent negative charge at pure air-water interfaces derived from electrokinetic experiments, this experimental fact has presented a source of intense debate since the mid 19th century. Here, we calculate surface tensions and ionic surface propensities at air-water interfaces from classical thermodynamically consistent molecular dynamics simulations. The surface tensions of NaOH, HCl and NaCl solutions show outstanding quantitative agreement with experiment. Of the studied ions, only H3O+ adsorbs to the air-water interface. The adsorption is explained by the deep potential well caused by the orientation of the H3O+ dipole in the interfacial electric field, which we comfirm using ab initio simulations.

Density ρ , sound velocity u , surface tension γ, viscosity η and conductance for (0.01 to 0.10 mol·kg − 1 ) alkyltrimethyl ammonium bromide (C n TAB, DTAB n = 12, TDTAB n = 14 and HDTAB n = 16) with (0.999 millimol·kg − 1 ) quercetin, apigenin and naringenin flavonoids and (2 g·kg − 1 ) bovine serum albumin (BSA) in aqueous 10% DMSO (w/w) at T = 298.15, 303.15, 308.15 K and p = 0.1 MPa are reported. The ρ , u , γ and η data have calculated apparent molar volume V ϕ , isentropic compressibility k s , apparent molar isentropic compressibility k s , ϕ , intrinsic viscosity [ η ] and activation energy E ∗ , to determine the contribution of methylene ( CH 2 ) groups of C n TAB. The γ , surface excess concentration Г max , molecular surface area A min , hydrodynamic radius R h , hydrodynamic volume V h , friccohesity σ and k on increasing C n TAB alkyl chain length infer higher dispersion. Hydrophobicity of BSA in aq-DMSO with flavonoids is as quercetin n TAB develops stronger electrostatic and hydrophobic interactions with BSA and flavonoids denature native BSA structure. Increasing alkyl chain length has catalysed BSA with flavonoids on mutual interactions strengthening their interacting activities, proven with higher η and lower γ values.

The Butler equation (on the equality of the partial surface tensions of the components of a solution) is derived in this paper from the general requirement that in equilibrium the Gibbs energy of the solution phase (taking into account also its surface area) must have a minimum value. This new derivation hopefully will increase the confidence of the scientific community in applying the Butler equation in further calculations of surface tension and surface adsorption (and also surface phase transition) of liquid solutions and in extending it to other interfaces.

The influence of temperature on the dynamic surface tension of water in heptane vapour is studied using drop profile analysis tensiometry. The water drops are formed in air saturated by heptane and water vapours. For long life times a new phenomenon is found: a sharp decrease of surface tension from about 60 mN/m down to 30 mN/m. The time until this sharp surface tension sets in decreases with increasing temperature. This phenomenon is attributed to the formation of heptane adsorption layers with a significant thickness. To ensure that the sharp surface tension decrease is not an artefact, the experimental error (deviation of drop profiles from the Young-Gauss-Laplace equation) was determined using harmonic oscillations imposed to the surface of pure heptane drops. It was shown that fitting errors below 10 μm in the determination of the drop radius do not affect the calculated surface tension value. The sharp surface tension decrease was observed with fitting errors below 5 μm, so that this phenomenon was explained to be caused by the formation of multilayers. The surface tensions and adsorbed amounts are described by a model developed earlier. The experimental results depend essentially on the experimental method used. In another experiment the atmosphere in the measuring cell was pre-saturated only by water vapour, and heptane (pentane) was added onto the cell bottom just immediately before the water drop was formed. The increase of temperature results in a slower adsorption process which is opposite to the case where the composition of the mixed atmosphere inside the cell was established prior to the experiments.

Carbonated water has been recently proposed as an enhanced oil recovery method for crude oil reservoirs. Interfacial tension (IFT) plays a crucial rule on the displacement of trapped oil ganglia in the porous media. This investigation is designed to systematically assess the dynamic interfacial tension (DIFT) of two different types of crude oils with carbonated water (CW). In addition, the measured experimental data were applied into specified models. The DIFT behavior of acidic and non-acidic crude oil samples/CW and deionized water (DW) are also compared to find the effect of dissolved carbon dioxide in water on IFT. At the next stage, DIFT of all the results were used through three different models namely diffusion-controlled, mono-exponential models and an empirical equation. In this way, induction, adsorption (i.e. relaxation or rapid fall), equilibrium and meso equilibrium times, diffusivity of surface active materials in the crude oil to the crude oil/aqueous phase interface (D SA ) and surface excess concentration of surface active components (Г SA ) of CW systems are calculated and compared with those of the crude oil-DW systems. While IFT reduction is considered as an effective mechanism of CW injection for more oil recovery, the obtained results in the current investigation show a contradicting trend. In details, the dissolved CO 2 reduces the pH of the aqueous phase, consequently, increases the basic natural surfactant ionization. The obtained results show that domination of Г SA reduction compared to the ionization of basic natural surfactant leads to IFT enhancement.

An alternative to the conventional ‘pore filling model’ for describing Gibbsian surface excess (GSE) isotherm from a liquid mixture on a porous adsorbent is proposed where the adsorbed phase volume is treated as a variable. The new model is tested using GSE isotherm data on various micro and mesoporous adsorbents. The adsorbed phase volume is found to be system specific but always less than the adsorbent pore volume, irrespective of the pore size.

Ionic liquids (IL) have emerged as a prospective new material for a wide range of industrial applications, owing to their unique structures and properties. Hence, understanding the structure–property relationships of IL is very important for both fundamental and industrial applications. In this study, a series of imidazolium-based IL with different chain lengths, namely C8mimBF4, C10mimBF4 and C12mimBF4, were synthesized. Their molecular structures were confirmed by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) analysis. Thermal gravimetric analysis (TGA) revealed that the IL synthesized were thermally stable in the desired temperature range. Dynamic light scattering (DLS) results of IL was analyzed in order to understand the effect of alkyl length on micellar size. Conductivity and surface tension measurements were carried out to determine the adsorption and aggregation characteristics in aqueous solutions. The influences of temperature as well as alkyl chain length on viscosity were also investigated. Surface adsorption parameters such as surface excess, minimum area, effectiveness and efficiency were also determined from equilibrium surface tension data. A careful analysis of the thermodynamic aspects of air-ionic liquid aqueous systems reveals that free energies of adsorption are favoured over micellization for all systems.

Surface tension dictates fluid behavior, and predicting its magnitude is vital in many applications. Equations have previously been derived to describe how the surface tension of pure liquids changes with temperature, and other models have been derived to describe how the surface tension of mixtures changes with liquid-phase composition. However, the simultaneous dependence of surface tension on temperature and composition for liquid mixtures has been less studied. Past approaches have required extensive experimental data to which models have been fit, yielding a distinct set of fitting parameters at each temperature or composition. Herein, we propose a model that requires only three fitting procedures to predict surface tension as a function of temperature and composition. We achieve this by analyzing and extending the Shereshefsky (J. Colloid Interface Sci. 1967, 24 (3), 317-322), Li et al. (Fluid Phase Equilib. 2000, 175, 185-196), and Connors-Wright (Anal. Chem. 1989, 61 (3), 194-198) models to high temperatures for 15 aqueous systems. The best extensions of the Shereshefsky, Li et al., and Connors-Wright models achieve average relative deviations of 2.11%, 1.20%, and 0.62%, respectively, over all systems. We thus recommend the extended Connors-Wright model for predicting the surface tension of aqueous mixtures at different temperatures with the tabulated coefficients herein. An additional outcome of this study is the previously unreported equivalence of the Li et al. and Connors-Wright models in describing experimental data of surface tension as a function of composition at a single temperature.

The surface thermodynamic properties play an important role in researching into the thermodynamics of nanoparticles involved in various chemical and physical processes. In this paper, the relations between surface thermodynamics properties, respectively, and particle size of nanoparticles were deduced. A new method of determining the surface thermodynamic properties of nano-copper by equilibrium constant was proposed. On the basis of the equilibrium constants of nano-copper with different particle sizes dissolved in sulfuric acid at different temperatures, the effect of particle size on the surface thermodynamic properties was investigated and the variation of surface tension with temperature was obtained. The influence regularities of size on the surface thermodynamic properties agree with the theoretical analysis. With the decrease in particle size, the molar surface Gibbs energy, the molar surface enthalpy and the molar surface entropy increase, and when the diameter exceeds 20 nm, the surface thermodynamic properties exhibit linear correlation with the reciprocal of diameter, respectively. The surface tension decreases with temperature increasing, and a linear relation between them is observed. This paper provides us a simple and reliable method to obtain the surface thermodynamic properties of nanoparticles for better understanding their thermodynamic behaviors in the chemical reaction, adsorption, melting, etc.

Mono-tetrapropylene diphenyl ether disulfonate (C12-MADS) and Di-tetrapropylene diphenyl ether disulfonate (C12-DADS) were synthesized via three steps reactions: Friedel-Crafts alkylation, sulfonation and neutralization. The surface properties and thermodynamic properties of micellization of tetrapropylene benzene sulfonate (C12-BAS), C12-MADS and C12-DADS were investigated by equilibrium surface tension, dynamic surface tension and electrical conductivity measurement. The result of surface tension shows that surface activity of gemini surfactant C12-DADS is better than that of C12-BAS and C12-MADS. The dynamic surface tension data show that the diffusion coefficients values of C12-MADS and C12-DADS are lower than that of C12-BAS, and the adsorption process of surfactants at air/water interface is a mixed diffusion-kinetic adsorption mechanism. In addition, the electrical conductivity result indicates that the C12-DADS more readily form micelles than other two.

The measurements of surface tension of aqueous solutions of rhamnolipid (RL) and surfactin (SF) at different temperatures were made. On the basis of the obtained results Gibbs surface excess concentration was determined at the water-air interface which next was applied for determination of the surface coverage by surfactant molecules as well as for calculation of the standard Gibbs free energy, enthalpy and entropy of adsorption. For determination of the standard Gibbs free energy of adsorption different known methods were analyzed and next applied. The obtained results were compared to those determined by the method proposed in this paper. Good agreement between the values of Gibbs standard free energy of adsorption determined from the proposed equation and the linear form of Langmuir adsorption isotherm as well as from the Langmuir equation modified by de Boer was obtained. To check the applicability of the proposed equation, the Gibbs standard free energy of adsorption was calculated for many other ionic and nonionic surfactants. The results of the calculations were compared to those determined using other methods. It appeared that there is the best agreement between the values obtained using the proposed equation and those calculated by the modified Langmuir equation.

Surface tension is one of the most important properties of liquid. A new theory is proposed and applied to the phenomena related to the surface tension of pure liquid compounds and strong electrolyte solutions. We first found that the phase transitions of pure liquid compounds from bulk to surface are exothermic and transition heats of 38 liquid compounds are determined quantitatively. This theory also describes successfully the variations of the surface tensions with the concentrations of solutes in strong electrolyte solutions. As a byproduct, minimum thicknesses of the surface layers of these solutions are deduced.

Surface tensions for aqueous NaCl, NaBr, NaI, KCl, KBr, and KI solutions have been measured at different temperatures and different concentrations. The liquid densities and activity coefficients for electrolyte solutions are modeled accurately with the ion-based statistical associating fluid theory (SAFT2). Besides, a new surface tension prediction model on the basis of the Gibbs thermodynamic method, coupled with ion-based SAFT2 is established, which is applied to predict the surface tension of aqueous concentrated salt solutions at different concentrations and temperatures. In this model, we derived the relationship between the activity coefficient and surface tension, and the activity coefficient can be calculated by ion-based SAFT2. The model is found to give accurate prediction for the surface tension of aqueous concentrated electrolyte solutions at different concentrations and temperatures with the parameter obtained at one fixed temperature.

A type of switchable tertiary amine Gemini surfactant, N,N′-di(N,N-dimethyl propylamine)-N,N′-didodecyl ethylenediamine, was synthesized by two substitution reactions with 3-chloro-1-(N,N-dimethyl) propylamine, bromododecane and ethylene diamine as main raw materials. The structure of the product was characterized by FTIR and 1H-NMR. We also investigated the surface tension when CO2 was bubbled in different concentrations of surfactant solution and the influence of different CO2 volumes on surface tension under a constant surfactant concentration. Finally the surface tension curve and the related parameters were acquired by surface tension measurements. The experimental results showed that the structure of the synthesized compounds were in conformity with the expected structure of the surfactant, and displayed a better surface activity after bubbling CO2. The critical micelle concentration (CMC) surface tension at CMC (γ cmc) pC20 (negative logarithm of the surfactant’s molar concentration C20, required to reduce the surface tension by 20 mN/m) surface excess (Γ max) at air/solution interface and the minimum area per surfactant molecule at the air/solution interface (A min) were determined. Results indicate that the target product had good surface activity after bubbling CO2.

The values of density and surface tension for aqueous solution of ionic liquid(IL) 1-butyl-3-methylimidazolium acetate([C4mim][OAc]) with various molalities were measured in the range of 288.15—318.15 K at intervals of 5 K. On the basis of thermodynamics, a semi-empirical model-molar surface Gibbs energy model of the ionic liquid solution that could be used to predict the surface tension or molar volume of solutions was put forward. The predicted values of the surface tension for aqueous [C4mim][OAc] and the corresponding experimental ones were highly correlated and extremely similar. In terms of the concept of the molar Gibbs energy, a new Eotvos equation was obtained and each parameter of the new equation has a clear physical meaning.

The present work deals with the physiochemical properties of polyoxyethylene sorbitan fatty acid esters (polysorbates), which are commonly known under the trade name Tween. Thermodynamics of micellization and adsorption at air-water interface for these nonionic surfactants solutions have been studied over a broad range of temperature. As the temperature of the surfactant solutions increases, the surface tension decreases whereas the critical micelle concentration (CMC) of each surfactant solution initially decreases and then increases. The free Gibb free energies of the micelle formation Δ G m o $\Delta {\rm{G}}_{\rm{m}}^{\rm{o}}$ , and the surfactant adsorption Δ G ads o $\Delta {\rm{G}}_{{\rm{ads}}}^{\rm{o}}$ , are calculated for the CMC of each surfactant at different temperatures. The surface or expanding pressure (Πcmc), minimum area per molecule (Amin), maximum surface excess (Γmax) are also calculated. The interfacial tension (IFT) between the aqueous surfactant solutions and the crude oil are measured at different concentrations of the surfactants using a spinning drop tensiometer. The contact angles are determined on an oil wet quartz surface to investigate the wettability alteration in the presence of Tween surfactants with varying salinity. FTIR analysis of quartz at dry and oil wet state, crude oil and COBRS (crude oil-brine-rock-surfactant) combinations are performed to identify the associated functional groups and their mutual interactions.

Three series of cationic gemini surfactants were prepared and characterized using elemental analysis and 1H-NMR spectroscopy. The surface properties of them, critical micelle concentration (CMC), surface excess concentration (Γmax) and minimum surface area per molecule (Amin) were evaluated via surface tension measurements. Quantum chemical parameters, such as the energy of the highest occupied molecular orbital (EH), the energy of the lowest unoccupied molecular orbital EL, the energy gap (ΔEg), dipole moment (μ), electronegativity (χ), hardness (η), electrophilicity (ω), hydrophobicity (Log P), approximated surface area (A) and the total energy of the optimized structure (ΔET), were theoretically calculated using the MNDO method.

A new ether-functionalized ionic liquid (IL), 1-ethyl-3-(2-methoxyethyl)-imidazolium dicyanamide, [C 2 2O1IM][DCA], was prepared and characterized. The values of density, surface tension and refractive index of the IL were measured at T = (298.15–338.15) K by using standard addition method (SAM) and the values of the molar surface Gibbs free energy were also calculated so that the molar surface entropy and the molar surface enthalpy of the IL were obtained. Using the concept of the molar surface Gibbs free energy, the traditional Eotvos equation was transformed into a modified Eotvos equation which can be well applied to the IL. In terms of the new scale of polarity for ILs, the polarity of [C 2 2O1IM][DCA] and 11 molecular liquids were estimated. The results show that the polarity order of these molecular liquids predicted by the dielectric constant is consistency with its estimated by the new scale of polarity for ILs.

The Gibbs Adsorption Isotherm equation is a two-dimensional analogous of the Gibbs-Duhem equation, and it is one of the cornerstones of interface science. It is also widely used to estimate the surface excess concentration (SEC) for surfactants and other compounds in aqueous solution, from surface tension measurements. However, in recent publications some authors have cast doubt on this method. In the present work, we review some of the best available surface tension experimental data, and compare estimations of the SEC, using the Gibbs isotherm method (GIM), to direct measurements reported in the literature. This is done for both nonionic and ionic surfactants, with and without added salt. Our review leads to the conclusion that the GIM has a very solid agreement with experiments, and that it does estimate accurately the SEC for surfactant concentrations smaller than the critical micellar concentration (CMC).

A three novel hydrophobic trioctylammonium-based protic ionic liquids (PILs) with 3,4-dimethylbenzoate, salicylate, and nonanedioate anions were synthesized and their structure were confirmed using nuclear magnetic resonance, elemental analysis and Fourier transform infrared spectroscopy. The three synthesized PILs were liquids at room temperature. The thermal properties were determined using thermogravimetric analyzer and differential scanning calorimetry. Density, viscosity, surface tension, and refractive index were measured for the synthesized PILs at temperature between 293.15 and 363.15 K at atmospheric pressure and as expected, it was found to decrease with increasing temperature. The density measurements were correlated as a linear function of temperature, and the viscosities were fitted to a Vogel-Fulcher-Tamman equation. The density measured values were used to calculate the molar volume, molecular volume, standard entropy, lattice potential energy and the isobaric thermal expansion coefficients, whilst the surface excess energy and entropy were calculated using the measured surface tension data. The di-cationic nonanedioate PIL was found to have higher viscosity, surface tension, heat capacity and onset decomposition temperature.