Mixed Adsorption Layers Research Articles

Electrochemical Measurements of the In(III) Ions Electroreduction; the Influence of Mixed Adsorption Layers ACT-CTAB and ACT-SDS

Using voltammetric and impedance methods, the effects of mixed adsorption layers ACT-CTAB and ACT-SDS on the kinetics and mechanism of In(III) ions electroreduction were investigated. Acetazolamide (ACT) was shown to catalyse the course of the electrode reaction (according to the cap-pair rule). The multi-step nature of the In(III) ions electroreduction process in each of the systems studied in the chemical step of formation of the active In(III) - ACT complexes in the adsorption layer playing an important role is demonstrated. The presence of the cationic surfactant CTAB increases the dynamics of acceleration of the In(III) ion electroreduction process by ACT, while the presence of the anionic surfactant SDS inhibits this reaction.

SURFACE PROPERTIES AND MICELLIZATION OF SODIUM ALKYLSULPHATES IN THE PRESENCE OF LOW-MOLECULAR ALCOHOLS

The process of micellization of sodium alkyl sulfates (SAS : sodium decyl- (SDS) and dodecylsulfate (SDDS)) of formation in aqueous solution without or with alcohols including propanol-1, propanol-2 and butanol-1 and their adsorption behavior at air-liquid interface were investigated with both the tensiometry and the conductometry at 298 K. The effect of chain length of alcohol on micellar and interfacial properties were discussed. Some parameters including surface excess concentration (Γmax), minimum area per surfactant molecule (Smin) at air-liquid interface, degree of ionization of micelle, and standard free energy of adsorption and micellization, etc. are estimated. It was experimentally established that the introduction of 0.5-1.0 mol/dm3 of alcohols into surfactant solutions contributes to the process of micellar formation of SAS and increases the stability of the micellar phase, as evidenced by the observed synergistic effect on the critical micelle concentration (CMC). The addition of different alcohols changes the values of Γmax, Smin, CMC of SDS and SDDS and induces an increase in degree of ionization (β) of micelle relative to that in pure water. When alcohols are introduced into SDS and SDDS solutions, the degree of ionization of micelles at a constant length of the alkyl radical of surfactant moderately increases with increasing alcohol content in the solution and ranges from 0.50-0.73 and 0.38-0.75, respectively. Also, the effect of alcohol was discussed. The obtained thermodynamic parameters were used to confirm these behaviors of interfacial adsorption or micellization. An increase in chain length of alcohol promotes the micellization process. The CMC values decrease with increasing length of the alkyl radical of alcohols. Propanol-1, compared to propanol-2, somewhat reduces the value of SDS and SDDS CMC to a greater extent. Standard free energy of micellization ∆G0mic, also confirms the micellization behavior. Standard free energy of adsorption (∆G0адс) indicates that an increase in the chain length of alcohol in aqueous solution is favorable to the adsorption of SDS and SDDS at air-liquid interface. A comparison of the values of the standard free energy of adsorption and micelle formation in sodium alkyl sulfates – alcohols – water systems showed that adsorption is the most thermodynamically advantageous process in the studies systems, and the packing of surfactant “molecules” in micelles is less dense, compared to packing in a mixed adsorption layer.

Regulating Lateral Adsorbate Interaction for Efficient Electroreforming of Bio-polyols.

Tailoring the selectivity at the electrode-electrolyte interface is one of the greatest challenges for heterogeneous electrocatalysis, and complementary strategies to catalyst structural designs need to be developed. Herein, we proposed a new strategy of controlling the electrocatalytic pathways by lateral adsorbate interaction for the bio-polyol oxidation. Redox-innocent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) anion possesses the alcoholic property that facilely adsorbs on the nickel oxyhydroxide catalyst, but is resistant to oxidation due to the electron-withdrawing trifluoromethyl groups. The alien HFIP adsorbents can compete with bio-polyols and form a mixed adsorbate layer that creates lateral adsorbate interaction via hydrogen bonding, which achieved a >2-fold enhancement of the oxalate selectivity to 55 % for the representative glycerol oxidation and can be extended to various bio-polyol substrates. Through in situ spectroscopic analysis and DFT calculation on the glycerol oxidation, we reveal that the hydrogen-bonded adsorbate interaction can effectively tune the adsorption energies and tailor the oxidation capabilities toward the targeted products. This work offers an additional perspective of tuning electrocatalytic reactions via introducing redox-innocent adsorbates to create lateral adsorbate interactions.

Regulating Lateral Adsorbate Interaction for Efficient Electroreforming of Bio‐polyols

AbstractTailoring the selectivity at the electrode‐electrolyte interface is one of the greatest challenges for heterogeneous electrocatalysis, and complementary strategies to catalyst structural designs need to be developed. Herein, we proposed a new strategy of controlling the electrocatalytic pathways by lateral adsorbate interaction for the bio‐polyol oxidation. Redox‐innocent 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) anion possesses the alcoholic property that facilely adsorbs on the nickel oxyhydroxide catalyst, but is resistant to oxidation due to the electron‐withdrawing trifluoromethyl groups. The alien HFIP adsorbents can compete with bio‐polyols and form a mixed adsorbate layer that creates lateral adsorbate interaction via hydrogen bonding, which achieved a >2‐fold enhancement of the oxalate selectivity to 55 % for the representative glycerol oxidation and can be extended to various bio‐polyol substrates. Through in situ spectroscopic analysis and DFT calculation on the glycerol oxidation, we reveal that the hydrogen‐bonded adsorbate interaction can effectively tune the adsorption energies and tailor the oxidation capabilities toward the targeted products. This work offers an additional perspective of tuning electrocatalytic reactions via introducing redox‐innocent adsorbates to create lateral adsorbate interactions.

Lysozyme binding with amikacin and levofloxacin studied by tritium probe, fluorescence spectroscopy and molecular docking

Lysozyme complexes with amikacin and levofloxacin were studied by spectroscopy approaches as well as using a tritium probe. Tritium was used as a labeling agent to trace labeled compound concentration in a system of two immiscible liquids and in the atomic form to determine the possible position of the binding site. Co-adsorption of protein and drug at the liquid-liquid interface was analyzed by scintillation phase method that allowed us to directly determine the amount of protein and drug in the mixed adsorption layer. Also, tensiometric measuring of the interfacial tension was used for calculation of binding parameters accordingly to Fainerman model. The treatment of complexes with atomic tritium followed by trypsinolysis and analysis of tritium distribution in the lysozyme peptides reveals the binding sites, binding energies in which were analyzed using molecular docking. Formation of complexes with amikacin and levofloxacin preserves secondar structure of protein. However, the formation of complex with amikacin leads to the almost total loss of the enzymatic activity of lysozyme and the redshift of the maximum on the lysozyme fluorescence band. A slight decrease in the distribution coefficient of lysozyme in the presence of amikacin assumes that the complex has higher hydrophilicity in comparison to lysozyme without additives. The most favorable for binding were the positions of the active centers that included amino acids Asp52 and Glu35, as well as in the vicinity of peptide His15-Arg21, with the participation of amino acids Tyr20, Arg14. In the case of levofloxacin, the formation of lysozyme-ligand complex in aqueous solution is possible without changing the microenvironment of the active center of the protein. Binding of levofloxacin to the active center of the enzyme was the most favorable, but Asp52 and Glu35 that are responsible for the enzymatic activity of lysozyme, were not affected.

Modification of stability properties of yttrium(III) oxide particles by simultaneous adsorption of poly(acrylic acid) and poly(ethylene glycol) for possible applications in wastewater treatment

The adsorption, electrokinetic and stability properties of yttrium(III) oxide—Y2O3 in mixed solutions of macromolecular compounds were investigated. The interfacial behavior of poly(acrylic acid)-PAA and poly(ethylene glycol)—PEG in single and binary systems was examined in the pH range 3–10. The polymers used were characterized by different ionic nature—the PAA is an anionic polymer, whereas PEG belongs to the group of non-ionic polymers. Based on the results obtained, the most probable mechanisms for the binding of PAA and PEG macromolecules on the yttrium(III) oxide surface were proposed. In addition, the analysis of adsorption and electrokinetic data enabled explanation of the obtained changes in the stability of Y2O3 suspensions without and in the presence of PAA or/and PEG, as well as determination of the specific stabilization-destabilization mechanisms of the studied systems. It was shown that yttrium(III) oxide modification by mixed adsorption layers of both polymers with different ionic character changes considerably the surface and stability properties of the examined solid suspensions.Graphical

Impact of acetazolamide on the double layer parameters at the R-AgLAFe/chlorates(VII) interface in the presence of ionic surfactants

Adsorption of acetazolamide (ACT) and formation of a mixed adsorption layers of acetazolamide (ACT)—sodium 1-decanesulfonate (SDS) and acetazolamide—hexadecyltrimethylammonium bromide (CTAB) at the R-AgLAFe/chlorates(VII) interface are described. The systems were characterized by the measurements of differential capacity, potential of zero charge, and surface tension at this potential. The adsorption parameters determined in the studied systems indicate the SDS domination in the adsorption equilibria and the competitive adsorption between the ACT—SDS or mixed micelles. However, acetazolamide dominates at adsorption equilibria of the ACT—CTAB mixture.

Interfacial properties, decompression, and augmented injection of amphiphilic carbon dots and surfactant mixtures

The mixing properties of amphiphilic carbon dots named C12-SCDs with a cationic surfactant (Dodecyl trimethyl ammonium bromide, DTAB) and an anionic surfactant (Sodium dodecyl sulfate, SDS) were investigated. Results indicated that surfactants DTAB and SDS show a synergistic effect in reducing surface tension with C12-SCDs. The synergistic effect of the DTAB/C12-SCDs mixture is more prominent than the SDS/C12-SCDs mixture, which may result from the electrostatic attraction between DTAB and C12-SCDs. Meanwhile, adding inorganic salts, the surface tension of these mixtures shows a trend of first decreasing slightly and then increasing. The DTAB/C12-SCDs mixture resists strong acids but not alkali environments. However, the surface tension of the SDS/C12-SCDs mixture gradually increases with the increase in pH. In addition, these mixtures have temperature-resistance properties. C12-SCDs and surfactants (DTAB and SDS) also have a synergistic effect in reducing the crude oil-water interfacial tension. Meanwhile, the DTAB/C12-SCDs and SDS/C12-SCDs mixtures have excellent wettability alternation performance. C12-SCDs and surfactants can form a mixed adsorption layer to promote the wettability alternation performance. The depressurization rates of DTAB, SDS, C12-SCDs, DTAB/ C12-SCDs mixture, and SDS/C12-SCDs mixture are 10.42 %, 11.54 %, 22.91 %, 26.32 %, and 24.75 %, respectively. The DTAB/C12-CDs and SDS/C12-CDs mixtures can effectively remove the oil film on the core surface, thus improving the channel of injected water. At the same time, these mixtures can be adsorbed on the surface of the hydrophilic core to form a hydrophobic surface, and the injection of water produces a hydrophobic slip effect. Finally, reducing the surface tension of water can also effectively reduce the injection pressure.

Adsorption of 4-aminopyrimidine at the R-AgLAFE/chlorate(VII) interface. Comparison of the adsorption properties of various water activity as well as different surfactants

The results of 4-aminopyrimidine (4-APM) impact studies on the double layer parameters at the R-AgLAFE/ chlorates(VII) interface in the solutions with different water activity as well as different properties of the mixed adsorption layer of 4-aminopirimidine – sodium 1-decanesulfonate (SDS) and 4- aminopyrimidine - hexadecyltrimethylammonium bromide (CTAB) at the electrode/solution interface are discussed.The differential capacity of the double layer (Cd) at the R-AgLAFE/ basic solution interface was measured using the electrochemical impedance spectroscopy. The zero charge potential (Ez) was determined using a streaming electrode, while the surface tension at the zero charge potential (Yz) was measured using the largest pressure method inside the mercury drop. It was proved that both the 4-aminopirymidine concentration and water activity have an essential effect on the doublelayer parameters on the R-AgLAFE/ chlorates(VII) interface. In the studied systems: 4-APM - SDS and 4-APM - CTAB, 4-aminopyrimidine dominance was observed.

Tensiometry-based sensing of aggregation and of evaporation behavior of a volatile amphiphile in mixed solutions with ionic and nonionic surfactants

Mixed surfactants solutions containing volatile amphiphiles, e.g. fragrances, are envisaged to exhibit correlations between aggregation behavior, molecular interactions, composition of the mixed adsorbed layers and the concentration of the volatile component in the vapors. These issues are addressed with tensiometric methods by considering dynamic and steady-state interfacial adsorption-evaporation behavior at both sides of air-liquid interface in mixed solutions of geraniol and micelle-forming ionic and non-ionic surfactants. Pendant drop tensiometry proved to be a sensitive method in assessing the concentration of geraniol in the vapors above mixed solutions. Differences in the release of the fragrance from the mixed interfacial layers are explained by competitive contributions of specific barrier mechanisms and concentration-dependent aggregation in bulk solutions. Synergetic effect in reducing surface tension was evident for mixtures of geraniol with anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) surfactants. Dynamic anti-synergetic effect in SDS-geraniol mixtures is attributed to strong aggregation behavior, which was found to hinder the evaporation of geraniol. Measurements of the headspace concentration indicated weak interactions between geraniol and micelles of non-ionic highly surface active Brij-35 surfactant. The presented results extend the traditional analytical toolbox for evaluating factors which affect the mass transfer of volatile organic amphiphiles between aqueous and gas phases.

Comparison of interfacial interactions between bovine serum albumin with water- and oil-soluble surfactants: An interfacial rheological study

The interfacial interactions between bovine serum albumin (BSA) with a water-soluble surfactant polyoxyethylene sorbitan monooleate (Tween 80) and an oil-soluble surfactant sorbitan monooleate (Span 80), respectively, were studied using the interfacial dilatational rheological experiments. The BSA molecules were irreversibly adsorbed at interface and formed a network with high dilatational modulus. The increasing interfacial pressure induced the transformation of BSA molecules from a compact globular to an unfolded flexible conformation, which enhanced the relaxation process. Tween 80 formed hydrophilic complexes with BSA in the aqueous phase, significantly slowing down the dynamic adsorption. In addition, Tween 80 played a dominant role at the interface due to its higher interfacial activity, thus inhibiting the interfacial performance of BSA. As BSA and Span 80 diffused towards the interface from different phases, they adsorbed rapidly at the interface and formed a mixed adsorption layer, thus exhibiting synergistic effects in decreasing the interfacial tension. However, the alternate arrangement of BSA and Span 80 at the interface disrupted the inter-protein interactions, resulting in a significant decrease in the dilatational modulus of the interfacial film. The obtained results showed that Span 80 from the oil phase and Tween 80 from the aqueous phase interacted with the protein in different ways, and thus presented distinct dynamic adsorption processes and interfacial performance. The present work provided a theoretical foundation for their practical application in food, cosmetic, and pharmaceutical industries.

INFLUENCE OF POLYVINIL ALCOHOL ON THE SURFACE PROPERTIES OF IONOGENIC SURFACTANT – TWEEN MIXTURES

A colloid-chemical approach was used to describe the process of surface concentration of Tweens (Tw-60, Tw-80), sodium dodecylsulfate (SDDS), chloride dodecylammonium (HDDA) from multicomponent aqueous solutions. The possibility of increasing the degree of flotation isolation of SDDS and HDDA when they are together in a solution with Tweens in the presence of polyvinyl alcohol (PVA) has been confirmed. During the flotation treatment of binary solutions of ionic (HDDA, SDDS) and nonionic (Tw-60, Tw-80) surfactants of different composition, the degree of flotation isolation increases be 10–25% on average when compared with their isolation from individual solutions. The addition of PVA, which is used as high molecular weight reagent, in the form of a 0.15–1.0% aqueous solution in the amount of 0.5–2.0 cm3 per 25–50 cm3 of a mixed surfactants solution lead to increase the degree of isolation of Tweens and SDDS. According to Rosen’s model, the composition of mixed adsorption layers at the boundary between the solution and air phases was calculated, as well as the parameters of intermolecular interaction in adsorption layers. For all mixtures of surfactants at any ratio of components, adsorption layers are formed, most of which are enriched with more surface-active Tw-60 and Tw-80. With the composition of the mixture of SDDS-Tw-60 n(SDDS): n(Tw-60)=0.7:0.3, almost equimolar adsorption layers are formed. At different mole rations of surfactants in mixed systems in solution, the molar fraction of Tw-60 in the adsorption layers of the HDDA-Tw-60 mixtures is greater than that of the SDDS-Tw-60 mixtures. The value βσ depends on the type and composition of the mixture, the nature of the surfactant. This effect is most pronounced at a high content n(Tween) = 0.7 in the solution (here the maximum values (by absolute value) of the intermolecular interaction parameter are observed. The expediency of using the parameter of surfactants in mixed adsorption layers to predict their surface concentration during isolation from multicomponent aqueous solutions and wastewater is shown.

Quantitative analysis and interfacial properties of mixed pea protein isolate-phospholipid adsorption layer

Proteins and low-molecular-weight (LMW) surfactants are widely used for the physical stabilization of many emulsion-based food products. This study investigated the oil-water interfacial behavior between pea protein isolate (PPI) and phospholipid (PL). The emulsions prepared with different concentrations of PPI and PL were stabilized by their synergetic or competitive adsorption at the oil-water interface. In addition, the quantitative proteomics results could illustrate the displacements of proteins by PL. The result showed that the vicilin (7S) could be preferentially displaced by PL. Meanwhile, the results of quartz crystal microbalance with dissipation (QCM-D) indicated the high affinity of legumin (11S) with PL, suggesting that the legumin possessed higher interfacial affinity to prevent interfacial displacement. This research could help us to understand the interaction and competitive adsorption between plant proteins and LMW surfactants profoundly, which could promote the development of plant protein-based emulsion beverage with improved stability.

Interaction of catalyst nanoparticles and pollutant molecules in photocatalytic wastewater treatment: Novel characterization via dynamic surface properties

In photocatalytic processes for wastewater treatment, the degradation reactions mainly occurs at the surface of the catalyst and nearby regions. Therefore, understanding of the interactions between the catalyst and pollutant in a photocatalytic degradation system is of utmost importance, determining the affinity of the pollutant molecules to be attracted or repulsed from the photocatalyst particles. The aim of this experimental study is to get a better insight about the interactions between the catalyst nanoparticles and pollutant molecules via a novel characterization method based on dynamic surface phenomena analysis. Drop profile analysis tensiometry (PAT) is used for this purpose for dynamic surface tension and elasticity measurements of dye solutions (as pollutants), and in mixed solutions with catalyst particles at different pH conditions. The results demonstrate that the cationic dye Malachit Green (MG) has a low surface activity at pH 6.5, with an equilibrium surface tension about 69 mN/m. While it becomes much more surface active at pH 9 and surface tension is decreased to 59 mN/m. Adding TiO2 nanoparticles to MG solution at pH 9 causes a significant increase in surface tension, with much slower dynamics of adsorption at air/water interface. These results indicate a significant attraction and attachment of MG molecules to the surface of TiO2 nanoparticles, creating MG-TiO2 complexes, which have mobility much slower than the free MG molecules. This observation is in a good correlation with observed higher efficiency of MG degradation around pH 9. The capability of this novel experimental protocol is also examined for the anionic dye Eriochrom Black-T (EBT). According to the results, a significant interaction between TiO2 nanoparticles and EBT exist at pH 3, which is also well in accordance with reported higher efficiency of EBT degradation around pH 3. The elasticity measurements performed in this work, also support these results as an important characterization parameter for estimation of the molecular interactions in mixed adsorbed layers.

Simultaneous removal of inorganic and organic pollutants from multicomponent solutions by the use of zeolitic materials obtained from fly ash waste

Fly ash is an energy waste considered as a global environmental hazard. Annually, it is generated in the amount of over 50 million tons. One of the ways of fly ash management is its conversion into porous structures, which then can be applied to capture other pollutants from the aquatic environment. This paper presents the adsorption capabilities of four products of hydrothermal reaction of fly ash (HC FA), i.e., zeolites (Na-X, NA-P1) and their composites with carbon (Na-X(C), Na-P1(C)). All five materials were characterized in terms of their structure and used as adsorbents of heavy metals (Pb(II), Zn(II) ions) and organic compounds (diclofenac – popular anti-inflammatory drug, poly(acrylic acid) – polymer commonly used in industry) from their mixed solutions. Adsorption–desorption, electrokinetic and stability measurements were performed to determine the mechanisms driving the formation of the mixed adsorption layers. It was found that Na-X zeolite adsorbed 322.1 mg/g of Pb(II), 332.5 mg/g of Zn(II) and 6.68 mg/g of DCF, whereas Na-P1 bounded 332.9 mg/g of Pb(II), 103.6 mg/g of Zn(II) and 21.19 mg/g of DCF. In the mixed systems of adsorbates, these values were different, but also satisfactory. For example, in the Zn(II) presence, the adsorption of DCF on Na-X increased from 6.68 to 12.86 mg/g and that on Na-X(C), from 8.49 to 21.95 mg/g. The adsorbed pollutants changed the structure of electrical double layer of zeolitic materials. Moreover, they affected the stability of the examined suspensions. The presented results are promising for the further application of obtained zeolitic materials for environmental remediation.Graphical

Aggregation mechanism of natural schwertmannite particles covered with two-component layers of high molecular weight tackifier and trace metal ions

This paper aimed at the aggregation mechanism of natural schwertmannite (SCH) particles covered with layers composed of two different substances, i.e., trace metals (cadmium (Cd), copper (Cu)) and commercial polyacrylamide tackifier (PAM). The mineral applied was taken from the Muskau Arch area (Poland) and characterized. Coating of SCH with Cu, Cd, and PAM was conducted in the systems containing one- or two substances. To estimate the mineral aggregation with and without specific adsorption layers, the stability study was carried out. The obtained results indicated that the accumulation of both trace metal ions and polymer was higher in the mixed adsorption layers. Then, the adsorption efficiency of Cd increased even by 25.10% (pH 5). The highest growth in the PAM adsorption was noted at pH 6, i.e., by 49.73% (in the presence of Cu) and 42.80% (Cd). The aggregation of the SCH particles covered with mixed adsorption layers was stronger than that without adsorbates. Under these conditions, the turbidity of the system was only 57.2 NTU (Nephelometric Turbidity Units), whilst after 60 min, 54.4 NTU. In the simultaneous presence of PAM and trace metal ions, the solid particles formed flocs of considerable size. The polymer formed specific bridges between them and thus facilitate their contact (flocculation). What is more, trace metal ions mediated connection of the particles coated with PAM.

Influence of mixed 2-thiocytosine–ionic surfactants adsorption layers on kinetics and mechanism of Bi(III) ions electro reduction: use of the nanostructured R-AgLAFE

The nanostructured cyclically refreshable liquid amalgam film silver-based electrode (R-AgLAFE) was applied to study of the Bi(III) electrode process in the presence of 2-thiocytosine and selected ionic surfactants. The application of voltammetrictechniques (SWV, CV, DC), as well as electrochemical impedance spectroscopy (EIS) allowed the determination of the kinetic which in turn, defined the 2-thiocytosine catalytic effect and also their correlation in the presence of surfactants. The presence of mixed 2-thiocytosine-CTAB and 2-thiocytosine-SDS adsorption layers affects the mechanism and kinetics of Bi(III) ions electro-reduction process in chlorate(VII). CTAB and SDS change the dynamics of the catalytic impact of 2-thiocytosine on Bi(III) ions electro reduction. In both cases, the Bi–(RS–Hg) complex plays a key role, as it is the 2-thiocytosine that dominates in the establishment of the adsorption equilibria of the studied mixed adsorption layers.

SURFACE TENSION AND ASSOCIATION IN AQUEOUS SOLUTION SURFACTANTS IN THE PRESENCE OF POLYACRYLAMIDE

The surface tension of aqueous solutions of cationic (dodecylammonium and dodecylpyridinium chlorides) and anionic (sodium dodecylsulfate) surfactants was measured in the presence of polyacrylamide in the solution. A synergistic effect of reducing the surface tension of mixed solutions of cationic surfactants, in the region of sufficiently high concentrations of mixed solutions of sodium dodecyl sulfate, with polyacrylamide in the range of molar ratios of the mixture components - n (Surfactants : PAA) = 1: 1; 1: 0.25 was established. The values ​​of the maximum adsorption, the values ​​of the area per molecule or associate of surfactants in the adsorption layer, as well as the standard Gibbs free energy of adsorption of surfactant - PAA associates are calculated. In accordance with Rosen's model, the composition of mixed adsorption layers at the solution-air interface is calculated, as well as the parameter of intermolecular interaction in adsorption layers between molecules, cationic and anionic ions surfactants and PAA. The values ​​of the critical micelle concentration (CMC) of individual surfactants in aqueous solutions exceed the CMC of the studied surfactants in the presence of PAA, which promotes micelle formation.

Анализ мицеллообразования и адсорбционных слоев бинарных смесей компонентов сульфатного мыла

Currently, the main trend of the pulp and paper industry development is bio-refining. It is based on integrated and deep processing of wood raw materials to obtain products with higher value added and reduced amount of waste. One of the high priority tasks of bio-refining is improvement of technology of by-product (sulphate soap) extraction from spent liquor with an increase in the yield and quality of the resulting product and a decrease in the level of environmental pollution. The complexity and energy intensity of sulphate soap extraction from spent liquor depends on many factors, including the species used for wood cooking, composition of extractives, the method of wood preparation for delignification, etc. Sulphate soap is a multicomponent emulsion with a predominant content of resin and fatty acids, small amount of unsaponifiable substances and an admixture of lignin, which is mainly extracted from waste liquior by settling. The low degree of its extraction is associated with the absence of systematical data on the mutual influence of the sulphate soap components. In this work, the patterns of intermolecular interaction of the individual components of the by-product (sulphate soap) are found. For this purposes the critical concentration of micelle formation (CCM) and surface tension depression of surface-active sodium oleate and sodium abietate and their mixtures of varying compositions were determined by the methods of tensiometry and conductometry. A detailed analysis of its mixed micelles and adsorption layers was carried out using the Rubin–Rosen pseudophase model. The interaction mechanisms of components in mixtures are explained. The impact on the composition of micelles and adsorption layers of the more surface-active sodium oleate was detected in mixed solutions. A maximum synergistic effect of micelle formation was observed in mixtures with a predominant content of sodium abietate. Analysis of experimental data and the result of sulphate soap modeling allow substantiating the complexity of its extraction from waste liquor after wood cooking with the presence of hardwood over 30 %, which is explained by the reduced content of resin acids in black liquor. For citation: Yakubova O.S., Demiantseva E.Yu., Smit R.A., Dubovy V.K. Analysis of Micelle Formation and Adsorption Layers of Binary Mixtures of Sulphate Soap Components. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 6, pp. 196–205. DOI: 10.37482/0536-1036-2021-6-196-205

Stabilisation of cosmetic compositions using combined emulsifiers

Objectives.This study investigated the surface properties and micelle formation of combinedstabilizers, which are a mixture of ionic and nonionic surfactants or different nonionic surfactants,to establish a correlation between the composition of stabilizers and the colloidal–chemicalproperties of direct emulsions obtained in their presence.Methods.The surface tension at the interface between the aqueous solutions of the combinedstabilizers with air and toluene was measured using a digital tensiometer. The sedimentationstability of the emulsions was assessed by the volume of the exfoliated water and oil phasesfor seven days. The particle sizes of the dispersed phase were determined using an OlympusCX3 bright field microscope equipped with a universal serial bus video camera connection. Therheological properties of the emulsions were evaluated using a rotary viscometer.Results.According to the isotherms of the surface tension of aqueous surfactant solutions atthe interface with air and toluene at emulsion preparation temperatures of 50 °C and 65 °C,a mixture of nonionic surfactants exhibited a higher surface activity and lower critical micelleconcentration at the interface with toluene. The optimal amount of stabilizers providing stabilityto the compositions for one month was 4 mass % for a mixture of anionic surfactants and nonionicsurfactants and 7 mass % for mixtures of different nonionic surfactants. Emulsions obtained in thepresence of a mixture of anionic and nonionic surfactants exhibited higher kinetic sedimentationstability values due to the formation of electrostatic and steric stabilization factors in the system.The developed compositions were microheterogeneous systems, the average droplet diameter ofwhich varied within the range of 1.0–5.7 µm. In terms of rheological properties, emulsions wereclassified as liquid-like structured systems with coagulation structures; the strength of singlecontacts between particles of the dispersed phase was (1.6–27.0) × 10-10N.Conclusions.A comparison of the physicochemical characteristics of the compositions obtainedin the presence of organic emulsifiers showed that emulsions stabilized using a mixture of ionicand nonionic surfactants, which form mixed adsorption layers, exhibited the best set of properties.