Mixed Adsorption Layers Research Articles

Lysozyme-dalargin self-organization at the aqueous-air and liquid-liquid interfaces

An experimental study of protein-peptide binding was performed by means of radiochemical and spectroscopic methods. Lysozyme and dalargin were chosen due to their biological and physiological importance. By means of tensiometry and radiochemical assays, it was found that dalargin possesses rather high surface activity at the aqueous-air and aqueous-p-xylene interfaces to be substituted by protein. Dalargin forms a hydrophobic complex with lysozyme in which the secondary structure of lysozyme is preserved. When lysozyme forms a mixed adsorption layer with dalargin at the aqueous-air surface, the peptide prevents protein from concentrating in the subsurface monolayer. In the presence of p-xylene protein in the interface, reorganization occurs quickly, so there is no lag in the interfacial tension time dependence. The interfacial tension in this case is controlled by protein and/or protein-peptide complexes. An increase in the enzymatic activity of lysozyme in the presence of dalargin was confirmed by a docking model that suggests the formation of hydrogen bonds between dalargin and amino acid residues in the active site.

Influence of physico-chemical parameters of surface-active systems components for minimization of evaporation of hydrocarbon liquids

Highly efficient stable aerated hydrophilic compositions containing fluorotensides and ultralight microdisperse systems using gas-filled glass, aluminosilicate and polymer microspheres have been developed. Designing the compositions of PAS based on the surface activity of surfactants, their solubility in water and the ability to bind water and the formation of hydrogen bonds between the components. The main condition for the stability of the coating when mixing the components - the chemical interaction between them and the formation of a system that does not dissolve in hydrocarbons and does not break down in terms of use. The best film-forming characteristics necessary for the operation of the coating (simultaneous reduction of surface tension and film formation) active substances (FPAR), the non-polar part of the molecules of which contains a fluorocarbon chain, so they are insoluble in hydrocarbons, well soluble in water and easily distributed on the surface of hydrocarbon liquids, creating a protective film. The choice of co-surfactants was based on the ability to stabilize hydrophilic films on the surface of hydrocarbons not only at favorable HLB, but also at the lowest, although higher than the critical concentration of micelle formation (CCM), concentrations for forming a mixed adsorption layer of increased strength. This surfactant was water-oil-soluble twin-80, which will significantly increase the hydrophilic part and enhance the stability of the PAS and the stability of the aerated system. The introduction of glass microspheres into the components of the system has significantly enhanced its strength and stability. In the study of the stability and gas permeability of the developed surfactant systems, it was found that the insulating ability of the coating increases with increasing hydrophilic-lipophilic balance of the system and due to chemical interaction between the carboxyl group of fluorotenside and hydroxyl groups of surfactants.

Синергизм действия в бинарном растворе неионогенного и анионного ПАВ.

Adsorption at the gas —air interface and micelle formation in binary solutions of ethoxylated alkyl phenol (Neonol AF 9-10) and sodium oleate have been studied. The Rubin and Rosen equations were used to determine the interaction parameters and the composition of mixed micelles and adsorption layers depending on the initial solution composition. The authors have found out that the micelles and the adsorption layer at the interface are enriched in a non-ionic component. The maximum synergistic effect during micelle formation was found for solutions containing 20–30 % molar of reagent Neonol AF 9-10, and during adsorption —20 and 50 %.

Role of surfactant adsorption and surface properties for the efficiency of PDMS-silica antifoams

We study how the composition of various surfactant mixtures affects the efficiency of mixed PDMS–silica antifoam in foamed surfactant solutions. First, systematic experiments are performed to characterize the surface and foam film properties of the studied surfactant solutions. The spreading, bridging and entry coefficients are calculated and the spreading ability of the antifoam is characterized by microscopy observations and by surface tension measurements. Next, the initial antifoam activity and the antifoam durability are characterized in foam tests. The obtained results reveal that the antifoam efficiency in solutions of low-molecular mass surfactants with low surface dilatational modulus depends strongly on the density (area-per-molecule) of the respective adsorption layer. The addition of nonionic surfactants, which increase the mean area-per-molecule in the mixed adsorption layer, enhances significantly the antifoam activity and durability. In contrast, the addition of surfactants, which decrease the mean area-per-molecule, suppresses the antifoam activity. Furthermore, we found that surfactant mixtures which form condensed adsorption layers on the solution surface suppress strongly the antifoam activity. As an extreme, the condensed adsorption layer formed from the natural surfactant Quillaja saponin suppresses the antifoam spreading even at highly positive spreading coefficient which results also in very poor AF efficiency. The obtained results rationalize in a coherent way the observed differences in the AF activity and durability in mixed solutions of various ionic, nonionic and zwitterionic surfactants.

Significantly enhancing lubricity and anti-wear performances of glycerol lubricant with urea-functionalized imidazolium-organophosphate ionic liquid as additive

A urea-functionalized imidazolium-organophosphate ionic liquid (M-16-EDHPA) was synthesized and investigated its tribological performance as a lubricant additive for glycerol. We performed solubility test and thermogravimetric analysis of neat samples. Research results demonstrate that adding 1.0% urea-M-16-EDHPA can improve the tribological properties of glycerol system. Wear scar surface was analyzed using SEM, EDS, XPS and TOF-SIMS to study the lubricating mechanism of M-16-EDHPA additive. The formation of a dense and stable boundary film composed of a mixed adsorption layer and a composite tribo-film is the reason for the excellent lubricity and wear resistance of M-16-EDHPA.

Adsorption of Sodium Hexadecyl Sulfate and Triton X from Binary Aqueous Solutions at Thermally Graphitized Carbon Black

Adsorption of anionic sodium hexadecyl sulfate (SHS) and nonionic Triton X surfactants with different ethoxylation degree: TX-45, TX-100 and TX-300 from their individual and mixed aqueous solutions at the surface of thermally graphitized carbon black (CB) was studied. It was found that at low solution concentrations addition of the nonionic surfactant increases the amount of SHS adsorbed from SHS/Triton X mixtures compared to SHS amount adsorbed from its individual solution. These findings might be explained by decreasing in electrostatic repulsion between SHS ions due to inclusion of the molecules of the nonionic surfactant in the mixed adsorption layer. At higher solution concentrations, adsorption of SHS decrease as a result of displacement of SHS ions from the mixed adsorption layer by Triton X molecules. It was established that the composition of the mixed adsorption layer at CB surface notably differ from the composition of the surfactant mixture in the bulk solution. The mixed adsorption layer is enriched with the molecules of the nonionic surfactants and this conclusion is confirmed by the results of measuring zeta potential of CB particles with the adsorbed surfactants.

Electric-Field-Induced Interface Behavior of Dodecyl Sulfate with Large Organic Counterions: A Molecular Dynamics Study.

Dodecyl sulfate with tetramethylammonium counterions has been employed to systematically investigate the influence of different static electric fields on molecular structural properties, surface tension, by adopting molecular dynamics (MD) simulations with IR and sum frequency generation (SFG) spectrum calculations. The results indicated that dodecyl sulfate (DS-) and large organic TMA+ counterions can form a mixed adsorption layer in which one head group of DS- is surrounded by two tetramethylammonium (TMA+) and one water molecule. Additionally, it was observed that the surface tension significantly decreases with the increasing static electric field strength since the surfactant stands straighter at the interface as the electric field increases. The result can be instructively adopted in the manufacturing field to control surface tension. Moreover, it was found that the SFG stretch intensities of methylene decrease and the stretch intensities of the methyl group increase with increasing static electric fields. The result indicated that the static electric fields can make DS- more orderly and upright at the interface.

Aggregation and thermal properties of nanostructured montmorillonite covered with mixed adsorption layers of cationic polyacrylamide and hazardous lead(II) ions

The aim of the study was to investigate the influence of nanostructured montmorillonite surface modification by the cationic polyacrylamide and the lead(II) ions on the thermal and aggregation properties of solid particles covered with mixed adsorption layers. The effects of cationic groups content in the polymeric macromolecules, the order of individual adsorbates addition, and lead(II) ions concentration were determined. Using spectrophotometry, potentiometric titration, microelectrophoresis, turbidimetry, DCS (Differential Centrifugal Sedimentation) and thermal analysis methods, the adsorption, electrokinetic, aggregation properties, as well as the thermal stability of studied montmorillonite—CT PAM—Pb(II) systems were established. It was shown that applied polymeric substance (soil flocculant) causes accumulation of lead(II) ions, which are hazardous at very low concentrations. Nevertheless, the chemical nature of these interactions may limit the bioavailability of this heavy metal for plants.

Change in the dynamics of the catalytic action of azathioprine on the electroreduction process of Bi(III) ions under the influence of surfactants in the context of controlled drug release

The influence of mixed adsorption layers of azathioprine – Tween 80 as well as azathioprine – Triton X-100 on the multi-step process of Bi(III) electroreduction in chlorates(VII) was studied using EIS and other electrochemical methods. It has been shown that there is control of multistage process of electroreduction of Bi(III) ions through the chemical reaction of the formation of Bi - AZA active complexes on the electrode surface, which mediate electron transfer. Active complexes are a substrate in the process of electroreduction and their different structure and properties are the reason for the diverse catalytic activity of azathioprine. On the other hand, the Bi(III) ions electroreduction process becomes slower in the presence of mixed adsorption layers, because the surfactant molecules block the electrode surface.

Surface tension at the interface between aqueous solution of surfactant and alkane. A comprehensive quantum chemical and thermodynamic approach

A thermodynamic model is used to analyse the adsorbed layers of CnDMPO (n = 12, 13), CnTAB (n = 10, 12, 14, 16) and SDS at the aqueous solution/hexane and aqueous solution/dodecane interfaces. The combined model assumes that the adsorption of alkane from the oil phase is governed by the Frumkin model, and the adsorption of the surfactant molecules from the solution obeys the reorientation model. We are able to show that at low surfactant concentrations a remarkable decrease of interfacial tension occurs due to a cooperative formation of a mixed adsorption layers by surfactant and alkane molecules. By a quantum chemical semi-empiric (PM3) simulation we analyse the orientation of oil and surfactant molecules in the interfacial layer, and calculate the relative amounts of adsorbed surfactant and alkane. The values obtained from the thermodynamic models agree well with those results calculated via the PM3 simulation. The results show, that at the interface the short-chain hexane molecules can form bi-layers with the long-chain surfactants, while the dodecane and surfactant molecules having commensurable chain lengths are mainly forming mixed monolayer.

Mixed adsorption of hexadecylpyridinium bromide and Triton X surfactants at graphitized carbon black

Adsorption of cationic 1-hexadecylpyridinium bromide (HDPB) and non-ionic p-(1,1,3,3-tetramethylbutyl)-phenoxypolyoxyethylene glycols surfactants of the Triton X series (Triton X-45, Triton X-100 and Triton X-305) from their single and mixed aqueous solutions at thermally graphitized carbon black (CB) was studied. It was shown that the adsorption of the non-ionic surfactant from its individual solution decreased when a number of ethylene oxide units in the surfactant molecule increased. Addition of the non-ionic surfactants increased the amount of HDPB adsorbed from HDPB/Triton X mixtures. At low solution concentrations it was found that in HDPB/Triton X mixtures, the experimental values of total surfactants adsorption are higher than the adsorption values calculated for the ideal surfactant mixtures. The composition of the mixed HDPB/Triton X adsorption layer and the parameters of the intermolecular interaction (?s), between the components in this layer, were calculated using the Rubingh-Rosen approach. It was shown that ?s parameters have negative values, which indicate notable interactions between Triton X molecules and HDPB ions in the mixed adsorption layer. It was found that the composition of the mixed adsorption layer at CB surface is notably different from the surfactants composition in the bulk solution. The mixed HDPB/Triton X adsorption layer is enriched with Triton X surfactant and the mole fraction of Triton X increases with decreasing of ethoxylation degree of its molecules.

Изучение динамических особенностей межфазного натяжения казеината натрия и хитозана на границе с маслом

In this paper, it was investigated the dynamic characteristics of the reduction in the interfacial tension of sodium caseinate and chitosan at the interface with oil by the method of tensiometry (PAT-1). The features of the formation of mixed adsorption layers of emulsion stabilizers at liquid interfaces for use in encapsulation are investigated. The kinetics of lowering of the interfacial tension was studied, and the kinetic parameters of the formation of adsorption layers were calculated. It was established that the duration of the interfacial tension decrease was explained by slow diffusion of the macromolecular coil to the surface, conformational rearrangement of the static coils of macromolecules of the surface activity of the segments, which is reflected in the relaxation time value.

In English

The adsorption of cationic hexadecylpyridinium bromide and non-ionic oxyethylated octylphenols (TХ-45, TX-100, ТХ-305) surfactants from their mixed solutions at non-porous hydrophobic carbon sorbent such as thermal graphitized carbon black has been studied. The molar fraction of oxyethylated octylphenols in the mixtures was 0.2, 0.4, 0.6, and 0.8. The results have shown that the adsorption values of hexadecylpyridinium bromide depend on the total concentration of the surfactant and the composition of mixtures. It has been found that the molar fraction of nonionic surfactants in the mixed adsorption layers at carbon black surface decreases in the series: ТХ-45 > ТХ-100 > ТХ-305. The regularities of the change in the surface activity of the surfactant mixtures at the solution-solid sorbent interface with an increase in the total surfactant concentration in the solution correlate with those for the solution-air system, but are more pronounced. The areas per hexadecylpyridinium bromide and the oxyethylated octylphenols molecules in the adsorption layer while adsorbing from their binary solutions are lesser than ones for the surfactants adsorption from their individual solutions, and smaller than the corresponding areas at the solution-air interface. These findings indicate the consolidation of the adsorption layer at the solid surface and confirm that the surfactants adsorption at carbon black surface as associates.

Oil-water interfacial behavior of soy β-conglycinin–soyasaponin mixtures and their effect on emulsion stability

We investigated the dilatational rheology and dynamic interfacial tension of soy β-conglycinin (7S) and soyasaponin (Ssa) mixtures at the oil-water interface, followed by the formation and short/long-term stability of the subsequent emulsions to evaluate the mechanism(s) of stabilizing emulsions using a fixed concentration of 7S (0.5%) in all the samples. The presence of a low concentration of Ssa (0.05%) significantly affected the interfacial dilatational and emulsification properties although 7S dominated the interface. Higher concentrations of Ssa (0.1%–0.75%) showed synergistic effects on the changes in interfacial tension due to the interactions between 7S and Ssa. These effects were primarily attributed to the complexation of 7S with Ssa, thereby loosening the rigid conformation of the protein and unfolding 7S at the interface. Owing to the elasticity of the mixed adsorption layers, the interfacial 7S–7S and 7S-Ssa interactions were enhanced. The improved resilience to external deformations and interfacial behaviors of these mixed layers induced long-term stability (42 days) in these emulsions. These results provide a potential application for natural food additives in designing emulsions by modulating protein-saponin mixtures to induce long-term stability.

Surface modification of activated carbon by surfactants mixtures

Adsorption of surfactants is widely used for surface modification of different materials. Using of the mixtures of the surfactants in many cases is more attractive compared with single surfactants, however composition of mixed adsorption layers at solid surface was not sufficiently studied yet. In this work, the mutual effect of anionic and nonionic surfactants on the composition of the mixed adsorption layer on the surface of activated carbon (AC) was studied. Sodium hexadecyl sulphate (SHS) and oxyethylated octylphenol Triton X100 (TX-100) were used as anionic and nonionic surfactants, respectively. Mixed SHS/TX-100 systems have been studied over a concentration range of 0.1-8.0 mmol/L and the molar fractions of SHS in the mixtures were within 0.2-0.8. It was shown that the adsorption isotherms of SHS or TX-100 surfactants at AC could be describe by the Langmuir equation. For surfactants mixtures at low equilibrium concentrations, it was found that adsorption of SHS increases when TX-100 is present in the solution. This might be explained by the decreasing of electrostatic interactions between the head groups of SHS molecules in the mixed adsorption layers due to incorporation of the molecules of the nonionic surfactant. At higher total surfactant concentrations, SDS adsorbed at AC surface is replaced by TX-100 molecules and as result the nonionic surfactants is preferentially adsorbed on AC.

ANALYSIS OF INTERMOLECULAR INTERACTIONS IN MIXED ADSORPTION LAYERS OF SURFACTANTS

The adsorption of the surfactants mixtures of different chemical nature such as Triton X-100 and sodium hexadecyl sulfate at the surface of graphitized carbon black was studied. Using the model of phase separation (the Rubi–Rosen approach), the composition of the mixed adsorption layers and parameters of interaction between the surfactant molecules in the adsorption layers were calculated. It was found that mixed adsorption layers are enriched with molecules of the non-ionic surfactant Triton X-100.
 The purpose of the work was to study the adsorption of binary mixtures of surfactants of various chemical nature on the surface of non-porous hydrophobic carbon sorbent at different SAS ratio in mixtures.
 The results of calculations show that the composition of the adsorption layer on the surface of the GC is significantly different from the ratio of surfactants in the solution. The value of the parameter χ indicates that the mixed adsorption layer on the surface of the GC is enriched with non-ionic surfactant molecules, even with a small its content in the solution (αTХ-100 = 0,2). With an increase in the ТХ-100 molar fraction in the binary solution from 0,2 to 0,8 its share in the adsorption layer increases in approximately 1.5 times. Negative values of the interaction parameters βs indicate excessive attraction of the molecules and ions of the mixture components in the mixed adsorption layers. An increase in the absolute value of the parameter βs with an increase in αTХ-100 in the solution characterizes the enhancement of the interactions between the components in the adsorption layer.
 Thus, in the course of experiments carried out for mixed systems of SHDS-ТХ-100, the existence of a synergistic effect in relation to an increase in the adsorption of surfactants on the GC surface was established. It is found that mixed adsorption layers are enriched with molecules of the non-ionic surface active substance of the triton X-100.

Molecular Interactions in Binary Surfactant Solutions: Effect of pH

By using surface tension and conductivity measurements, the colloid-chemical properties of the mixtures of cationic hexadecylpyridinium bromide with nonionic Triton X-100 surfactants were investigated both in the bulk solution and at air/solution interface at different pH values. The composition of mixed micelles and adsorption layers, parameters of molecular interactions in mixed micelles βm and adsorption layers βσ, as well as standard free energies of micelle formation ΔG0mic and adsorption ΔG0ads were calculated. It was found that molecules of the nonionic surfactant presumably dominate in the mixed micelles and adsorption layers. It was shown that βm and βσ have negative values, which indicate the strengthening of intermolecular interactions in the mixed micelles and adsorption layers. Based on the data obtained, it was suggested that ion-dipole interactions are involved in the formation of intermolecular structures between nonionic and cationic surfactants in aqueous solution and at the air-solution interface. It was shown that βm, βσ as well as ΔG0mic and ΔG0ads parameter depends on the solution pH value. The complex interplay of ion-dipole, protonation and chelation processes, which occur in the surfactant mixtures at different pH and affect the strength of intermolecular interaction, should be taken into account for data analysis.

Study on the Complex System of Sodium Lauryl Diphenyl Ether Disulfonate and Dodecyl Dimethyl Hydroxyethyl Ammonium Chloride

AbstractSurface chemical properties of the mixed system of sodium lauryl diphenyl ether disulfonate (C12-MADS, an anionic surfactant with double hydrophilic groups) and dodecyl dimethyl hydroxyethyl ammonium chloride (K3, a cationic quaternary ammonium surfactant) along with different proportion have been studied at 298 K and 318 K. Synergistic parameters of the mixture in the mixed micelles and the mixed adsorption layer were also calculated by using the regular solution theory. The composition of the mixed micelles and of the mixed adsorption layer was obtained. The results show that the surface chemical properties of C12-MADS/K3 mixture are better than either of single system, and when the solution ratio (α1 = [n (K3)/n (C12-MADS + K3)]) is 0.7 and 0.9, the surface tension curve has a double inflection point which indicates a synergistic effect between the surfactant molecules. The complex system showed a strong synergistic effect in the mixed adsorption layer and the mixed micelles. The mixed system of C12-MADS/K3 has synergism in surface tension reduction effectiveness, surface tension reduction efficiency and mixed micelle formation. When α1 is 0.67, the synergistic effect is the strongest.

Synergy between two protic ionic liquids for improving the antiwear property of glycerol aqueous solution

Abstract Two protic ionic liquids (PILs) were prepared and investigated on the tribological behavior of their different combinations in the glycerol-water mixture. Synergy between both PILs can remarkably enhance its antiwear property. Further, the tribological behavior of the optimal combination was explored considering different factors including concentration, temperature and load. All the concentrations demonstrate promising antiwear properties, though a 0.5% dose moderately outperforms other doses. The increase of temperature and load is favorable for the lubricating ability. Based on worn surface analyses and molecular dynamic simulations, the synergistic mechanism between both PILs as lubricant additives is ascribed to the coexistence of the mixed adsorption layers and the tribofilms containing sp2 bonded carbon, FeS and orthophosphate.

Thermal degradation of peat-based activated carbons covered with mixed adsorption layers of PAA polymer and SDS surfactant

The thermal behaviour of activated carbons obtained from peat and modified with poly(acrylic acid) - PAA films was examined. Additionally, the effect of anionic surfactant – sodium dodecyl sulfate (SDS) presence in the adsorption layer was determined. Three samples of activated carbons were analyzed: (1) sample N - obtained by pyrolysis of peat followed by steam activation, (2) sample N9C - obtained by physical activation of sample N with carbon dioxide and (3) sample N9K - obtained by chemical activation of sample N with potassium carbonate. TG, DTG and DSC coupled with FTIR and QMS spectrometry enable not only specification of thermal stability of examined systems, but also determination of main gaseous products of their thermal decomposition. The obtained results indicate that polymer/surfactant adsorption influences significantly the thermal degradation of used carbon materials.