Mixed Adsorption Layers Research Articles

Impact of water activity on double layer parameters at the mercury/chlorates(VII) interface in the presence of mixed adsorption layers of 6-mercaptopurine\u2013Triton X-100

Adsorption mechanism of 6-mercaptopurine, 6-mercaptopurine–Triton X-100 on the mercury electrode surface from 2, 4 and to 6 mol dm−3 chlorates(VII) was studied as the function of adsorbate bulk concentration. The experimental data obtained from the measurements of differential capacity of the double layer were used, namely the measurements of zero charge potential and surface tension at the zero charge potential. In the case of mixed adsorption layer of 6-mercaptopurine–Triton X-100 domination of 6MP in adsorption equilibria formation as well as competitive adsorption between the 6-mercaptopurine–Triton X-100 molecules were found. Significant contribution of water molecules in the adsorption–desorption processes was also observed.

Synergistic Effects Between the Two Choline-Based Ionic Liquids as Lubricant Additives in Glycerol Aqueous Solution

Two choline-based ionic liquids (ILs) were used as lubricant additives in the aqueous glycerol solution, and the tribological properties of their different combinations were investigated. They exhibit remarkable synergistic effects on the antiwear and friction-reducing abilities. The combinations of both ILs more significantly improve the lubricity of the glycerol solution compared with the independent additives. In addition, the tribological behavior of the optimal combination was explored under different temperature and load conditions. The lubricating property of the optimal additive formulation is weakened with the increase of temperature, but enhanced with the increase of load. The worn surfaces were analyzed using SEM-EDAX and XPS. Meanwhile, Monte Carlo simulations were performed to study the adsorption behavior of the additives on iron surface in the presence of water. Remarkable synergistic lubricating interactions between the ILs are ascribed to the formation of compact and stable boundary films composed of mixed adsorbed layers and complex tribofilms.

Controllable emulsion phase behaviour via the selective host-guest recognition of mixed surfactants at the water/octane interface

Emulsions are deeply involved in almost all aspects of the petroleum industry, especially in enhanced oil recovery. Supramolecular chemistry proposes a facile and controllable method to construct target assemblies. In this report, we investigated the effects of β-cyclodextrin (β-CD) on the emulsions stabilized by the mixed N-dodecyl-N-methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS). The additional β-CD exerted strong influences on the water/n-octane interfacial tension (IFT) between n-octane and the mixed L12/SDS aqueous solutions, which should be attributed to its selective host-guest recognition. Interestingly, the additional β-CD in moderate concentrations could selectively remove the major surfactant molecules at the interface to adjust the hydrophilic-lipophilic balance of the mixed adsorption layers, thereby causing the transformation of the emulsion type from O/W to W/O. The addition of excess β-CD would generate the construction of n-octane/β-CD complexes to enhance the hydrophilicity of the interfacial layers, which leads again to phase inversion. Emulsions and their types were characterized and confirmed by the measurements of their conductivities, average droplet radii and rheological properties. To verify the proposed mechanism for the multiple phase inversion, the effects of L12/SDS molar ratios and β-CD concentrations were studied in depth in the control experiments.

Вплив рН і йонної сили розчину на колоїдно-хімічні властивості бінарних сумішей поверхнево-активних речовин

Досліджено вплив рН і йонної сили розчину на міцелоутворення і адсорбцію бінарних сумішей гексадецилпіридиній броміду (ГДПБ) і тритону Х-100 (ТХ-100.).З використанням моделі фазового поділу (підхід Рубіна-Розена) розраховані склад змішаних міцел і адсорбційних шарів, параметри взаємодії в міцелах β m і адсорбційних шарах β σ , а також надлишкові вільні енергії міцелоутворення та адсорбції. Розрахунки складу змішаних адсорбційних шарів показали, що адсорбційний шар на межі розділу розчин – повітря у всьому інтервалі досліджених об'ємних співвідношень збагачений молекулами нейонної поверхнево-активної речовини (ПАР), що має вищу поверхневу активність. Встановлено, що збільшення йонної сили розчину призводить до зниження сили взаємодій ПАР в змішаному адсорбційному шарі. Це підтверджує електростатичну природу взаємодій у сумішах катіонних і нейонних ПАР. Ключові слова : поверхнево-активні речовини, адсорбція, бінарні суміші, міцелоутворення, адсорбційний шар

Influence of nonionic surfactants and water activity on to adsorption of 6-thioguanine at the mercury/chlorates(VII) interface

The mixed adsorption layers of 6-thioguanine-TritonX-100 and 6-thioguanine-Tween 80 formed at the electrode/chlorate(VII) interface are discussed. The systems were characterized by measurements of differential capacity, zero charge potential, and surface tension at this potential. It was found that 6-thioguanine dominates in the formation of adsorption equilibria of the studied mixture. Competitive adsorption between 6-thioguanine-Triton X-100 and 6-thioguanine-Tween 80, ClO ions or mixed micelles cannot be excluded.

Dynamic Properties of Mixed Cationic/Nonionic Adsorbed Layers at the N-Hexane/Water Interface: Capillary Pressure Experiments Under Low Gravity Conditions

Capillary pressure experiments are performed in microgravity conditions on board the International Space Station to quantify the dynamic interfacial behavior of mixed adsorption layers of TTAB and C13DMPO at the water/hexane interface. While the non-ionic surfactant C13DMPO is soluble in both bulk phases, water and hexane, the cationic surfactant TTAB is only soluble in the aqueous phase. The interfacial layer is thus formed by TTAB molecules adsorbing from the aqueous phase while the C13DMPO molecules adsorb from the aqueous phase, and transfer partially into the hexane phase until both the equilibrium of adsorption and the distribution between the two adjacent liquid phases is established. The experimental constrains as well as all possible influencing parameters, such as interfacial and bulk phase compressibility, interfacial curvature, calibration of pressure and absolute geometry size, are discussed in detail. The experimental results in terms of the dilational interfacial viscoelasticity of the mixed adsorption layers in a wide range of oscillation frequencies show that the existing theoretical background had to be extended in order to consider the effect of transfer of the non-ionic surfactant across the interface, and the curvature of the water/hexane interface. A good qualitative agreement between theory and experiment was obtained, however, for a quantitative comparison, additional accurate information on the adsorption isotherms and diffusion coefficients of the two studied surfactants in water and hexane, alone and in a mixed system, are required.

Possibilities of Using the Surface Concentration of Surfactant Mixtures for Wastewater Treatment

Correlation between the manifestation of synergic action of surfactants in the process of their adsorption at the binary solution–air interface and the efficiency of the surface concentration of surfactants has been found. The use of the parameter of intermolecular interaction of surfactants in mixed adsorption layers is shown to be expedient for predicting the surface concentration of surfactants during their extraction from multicomponent aqueous solutions and wastewater. The possibility of intensifying the flotation extraction of some ionogenic surfactants from aqueous solutions in the presence of Tweens has been confirmed.

The importance of the active complexes of 6 - mercaptopurine with Bi(III) with regards to kinetics and electrode mechanism changes in the presence of non-ionic surfactants

The presence of mixed adsorption layers affects the mechanism and kinetics of irreversible Bi(III) ions electroreduction process in 2 mol·dm−3 chlorates(VII). Triton X-100 and Tween 80 change the dynamics of the catalytic activity of 6-mercaptopurine (6MP) on Bi(III) ions electroreduction with the tendency of inhibition. Above the critical micelle concentration of Triton X-100 and Tween 80, the irreversibility of Bi(III) ions electroreduction decrease to the size comparable to the irreversible reduction of Bi(III) in 2 mol·dm−3 chlorates(VII) which can be associated with the electrode surface blocking by formed hemispherical surface micelles. It was proved that the unstable complexes of Bi – 6MP or mixed Bi – 6MP – TritonX-100 and Bi – 6MP – Tween 80 intermediating in electrons transfer, play a significant role in the multi-stage mechanism of the electrode process. The hydration shell and composition of active complexes change as well. The obtained regularities indicate that in this case confirmed changes in entropy are a decisive factor.

Research of Binary Surfactant Mixtures Based on N-Lauroyl Sarcosinate

Abstract Surface properties of binary surfactant systems of N-lauroyl sarcosinate (LS) with fatty alcohol polyoxyethylene ether (AEO9), dodecyl trimethyl ammonium chloride (DTAC) and dodecyl dimethyl betaine (BS-12) have been investigated in aqueous NaCl (0.1 mol · L−1) solution at (298 ± 0.1) K, respectively. Synergistic parameters of the two components in both mixed micelles and mixed adsorption layers were obtained by calculations. Furthermore, we applied the regular solution theory on the mixed systems when synergism in mixed micelle formation, surface tension reduction efficiency and surface tension effectiveness was researched. The results show that there are synergistic effects in the mixed systems, the surface performances of the mixtures are significantly better than that of any single component in the mixed systems. The result coincides with the relevant theories of the ability of mixed micelle formation, surface tension reduction efficiency and surface tension reduction effectiveness.

Properties of cucurbit[8]uril adsorption layer at the electrode/solution interface

Studies and quantification of cucurbit[8]uril properties at the electrode/solution interface in a wide range of the electrode potential and adsorbate concentration revealed features of its adsorption behaviour. It forms a mixed adsorption layer similar to cucurbit[7]uril, while cucurbit[6]uril does not.

Concentration effect of Quillaja saponin – Co-surfactant mixtures on emulsifying properties

HypothesisThis study examined the emulsifying properties of mixed surfactant systems of Quillaja saponins and food-grade co-surfactants (Na-caseinate, pea protein, rapeseed lecithin, and egg lecithin). We hypothesized to these mixtures may build mixed adsorption layers and thus enhance emulsion stabilization. ExperimentsOil-in-water emulsions (10%, pH 7) were prepared with different concentrations of co-surfactants (0.1–5.0%) alone or mixed with Quillaja saponins (0.05 or 0.5%). Dynamic interfacial tension measurements were performed to characterize the behavior of the surfactants at an oil-water interface. FindingsLow Quillaja saponin concentrations led to either no changes or substantial increases in particle sizes of protein stabilized emulsions, but d43-values decreased in lecithin stabilized emulsions at low lecithin concentrations. The dominating effect of Quillaja saponins at high concentrations led to formation of small droplets (d43≤2 µm) in all emulsions, except with 2.5% pea proteins. All co-surfactants showed synergistic or additive effects with respect to interfacial tension reductions upon addition of Quillaja saponins (except for egg lecithin with 0.005% Quillaja saponin addition). The results indicated a competing effect for saponin–protein interfaces, but formation of mixed saponin–lecithin interfaces, thus showing that the emulsion stabilization and interfacial properties can be tuned by specific binary surfactant mixtures.

Effects of mixed adsorption layers of 6-mercaptopurine – Triton X-100 and 6-mercaptopurine – Tween 80 on the double layer parameters at the mercury/chlorates(VII) interface

The mixed adsorption layers of 6-mercaptopurine (6MP) and neutral detergents at the mercury/chlorates(VII) interface are described. The adsorption parameters for the double electrical layer were calculated from the differential capacity measurements extrapolated to zero frequency. It was found that 6-mercaptopurine dominates in the formation of adsorption equilibria of the studied mixture. Competitive adsorption between the 6-mercaptopurine-Triton X-100 and 6-mercaptopurine – Tween 80 or mixed micelles cannot be excluded.

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

ABSTRACTVarious experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (∼2.0 × 10−3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50 = 25.04 µm) and was well emulsified with crude oil after the mechanical oscillation (D50 = 4.27 µm).

Lysozyme-surfactant adsorption at the aqueous-air and aqueous-organic liquid interfaces as studied by tritium probe

Self-organization of proteins and non-ionic surfactants at the aqueous-air and aqueous-organic liquid interfaces is controlled by hydrophobic interactions. Unfortunately, little is quantitatively known about the effects of high- and low-molecular weight non-ionic surfactants on protein adsorption and aggregation at aqueous-air and aqueous-organic liquid interfaces. A tritium probe technique was applied to the systems lysozyme – Pluronic P123 and lysozyme – Brij-35. For complex analysis, UV and fluorescent spectrometry were also used for solutions with the chosen protein and surfactants concentrations. Non-ionic surfactants form a flexible complex with lysozyme at the aqueous-air interface. We observed that both Pluronic P123 and Brij-35 result in displacement of 40–75 % of protein, even in a surfactant concentration range less than the CMC and rotation of residual protein (or protein in complex with surfactant) in the mixed adsorption layer compared to the adsorption layer formed by free lysozyme. In the mixed adsorption layer, lysozyme globules are separated, and protein becomes more available for tritium atoms compared to free lysozyme.

Self-organization of lysozyme—Ionic surfactant complexes at the aqueous-air interface as studied by tritium bombardment

The self-organization of lysozyme with cationic (dodecyltrimethylammonium bromide) and anionic (sodium dodecylsufate) surfactants at an aqueous-air interface was studied by means of tritium planigraphy. It was found that even if the surfactant concentration is too low to induce significant structural changes in the protein globule, the surfactant can bind with the protein via both electrostatic and hydrophobic interactions and can displace the protein from the interface. Different mechanisms of complex formation are suggested for lysozyme mixed with SDS or DTAB. SDS molecules screen positively charged groups of amino acid residues via electrostatic interactions and form hydrogen bonds with polar groups of amino acid residues. SDS also penetrates the protein globule via hydrophobic interactions. In contrast, DTAB interacts with hydrophobic amino acid residues, screening them from tritium atoms. For both surfactants, it was found that lysozyme maintains a longways-on orientation in the mixed adsorption layer.

Селективные свойства углеродного адсорбента, модифицированного смешанным адсорбционным слоем модификатора «жидкий кристалл – β-циклодекстрин» в условиях газо-адсорбционной хроматографии

Селективные свойства углеродного адсорбента, модифицированного смешанным адсорбционным слоем модификатора «жидкий кристалл – β-циклодекстрин» в условиях газо-адсорбционной хроматографии

Collagen-surfactant mixtures at fluid/fluid interfaces

The effect of three synthetic surfactants on surface activity and surface dilatational rheology of temperature-denatured type I collagen at water/air interface is described. An anionic (sodium dodecyl sulfate, SDS), a cationic (cetyltrimethylammonium bromide, CTAB) and a nonionic (Triton X-100, TX-100) surfactants were employed at variable concentrations (5×10−6molL−1–1×10−4molL−1). With the protein concentration fixed at 5×10−6molL−1, the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:3, 1:5, 1:10 and 1:20 were obtained. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic and equilibrium surface tension, as well as the surface dilatational moduli of the mixed adsorption layers formed at the water/air interface at pH 4.5. For the collagen-SDS mixtures, analogous studies were also performed at the water/tetradecane and water/olive oil interfaces. These results were complemented with the foam and emulsion formation ability tests, and the oil-in-water emulsions were characterized using Dynamic Light Scattering (DLS) and visual assessment.The most beneficial effect on surface activity, mechanical properties of adsorbed layer and foaming ability was observed for the mixtures of temperature-denatured collagen with SDS. The rheological parameters of the adsorbed layers formed by the same mixtures at the water/olive oil and water/tetradecane interfaces worsened significantly (values of rheological parameters E’ and E” are lower than values of E’ and E” of the adsorbed layers formed at the water/air interface). The corresponding emulsions, despite very low interfacial tension values, phase-separated within hours. We hypothesize that the poor kinetic stability was caused by flocculation due to collagen bridging between the oil droplets, resulting in emulsion creaming.

Effect of surfactants on surface activity and rheological properties of type I collagen at air/water interface

We describe the effect of three synthetic surfactants (anionic – sodium dodecyl sulfate (SDS), cationic – cetyltrimethylammonium bromide (CTAB) and nonionic – Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5×10−6molL−1 and the surfactant concentration was varied in the range 5×10−6molL−1–1×10−4molL−1, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV–vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC).Modification of the collagen structure by SDS at low surfactant/protein ratios has a positive effect on the mixture’s surface activity with only minor deterioration of the rheological properties of the adsorbed layers. The collagen/CTAB mixtures do not show that pronounced improvement in surface activity, while rheological properties are significantly deteriorated. The mixtures with non-ionic TX-100 do not show any synergistic effects in surface activity.

Adsorption of surfactants and proteins at the interface between their aqueous solution drop and air saturated by hexane vapour

The adsorption of proteins (β-lactoglobulin, β-casein) and the oxyethylated non-ionic surfactants C10EO8 and C14EO8 at the aqueous solution/air interface is strongly enhanced and accelerated by the presence of hexane vapour in the air phase caused by the co-adsorption of hexane molecules. Due to this hexane co-adsorption, the dependence of dilational visco-elasticity modulus on surface pressure is shifted towards larger surface pressure values. The adsorption kinetics of the studied non-ionic surfactants shows the same picture as that observed for the two proteins. In contrast, the desorption process of the hexane molecules from a pre-adsorbed mixed adsorption layer is very slow. This decelerated desorption is explained by a rather large desorption energy required by the hexane molecules. The experimental data are compared with several theoretical models developed earlier. The results allow estimating the activation energy for the hexane desorption from adsorption layers of the two studied non-ionic surfactants.

Molecular dynamics simulations on tetraalkylammonium interactions with dodecyl sulfate micelles at the air/water interface

Different Tetraalkylammonium (TAA+) counterions including tetramethylammonium (TMA+), tetraethylammonium (TEA+), tetrapropylammonium (TPA+) and tetrabutylammonium (TBA+) with dodecyl sulfate (DS−) at the air/water interface were studied with atom molecular dynamics (MD) simulations. Structural properties such as the distribution of polar head at the interface, probability of gauche defects, order parameters, length and angle distributions were investigated. The counterions and DS− form mixed adsorption layer. Our results show that weak CHO hydrogen bonds are formed between the polar head and alkane chains of counterions. The weak hydrogen bonds play an important role in the formation of mixed adsorption layer. Mainly four interaction patterns exit between TAA+ and DS− ions, in which binding pattern II, representing that two terminal methyl groups of TAA+ penetrate into the monolayer, is the most favorable one.