Adsorbed Surfactant Layer Research Articles

EFFECT OF SURFACTANTS ON THE REDUCTION OF LEAD(II) IONS ON LEAD ELECTRODE

The effect high molecular weight water-soluble surfactants with different functional groups have on the electroreduction of lead(II) ions on a lead electrode in various electrolytes is studied. A copolymer of methacryloylaminophenol with acrylic acid, a leather waste hydrolyzate, and a copolymer of monoethanolamine with vinyl ether acetate are used as surfactants. The electrolytes that are used are 1 M KCl, KBr, KNO3, HCOONa, NH2SO3H, 0.5 M Na2SO4, and 0.35 M Na3C6H5O7 .2H2O. It is shown that in 1.0 M KCl or KBr solutions, there is no inhibition of the electroreduction of lead(II) ions by the adsorption layers of surfactants. It is found that the inhibitory effect of polymers on the electroreduction of lead(II) ions in different background electrolytes increases in the order KCl > KBr > Na3C6H5O7.2H2O > Na2SO4 > KNO3 > HCOONa > NH2SO3H. Key words: lead ions, electroreduction, surfactants, electrolyte, lead electrode, exchange current.

Decrease in hydrophilicity and moisture readsorption of lignite: Effects of surfactant structure

The low moisture content of lignite is essential to its high utilization efficiency. There has been increasing attention given to the adsorption of surfactants to decrease the hydrophilicity and moisture readsorption of lignite. This has focused on findings surfactants that are effective, convenient, and inexpensive. To understand the effect of surfactant structure on decreased lignite hydrophilicity, eighteen surfactants including conventional types of surfactants were used for lignite treatment. Wetting heat results indicated that cationic and non-ionic surfactants were superior in their performance to decrease the hydrophilicity of lignite compared to anionic surfactants with the same hydrophobic alkyl chain. Ethanediyl-1,2-bis(dimethyl dodecyl ammonium bromide) (12-2-12) and lauryl polyoxyethylene ether (C12EO9) were found to be the most effective cationic and non-ionic surfactants in these samples, respectively. Linear shapes, long alkyl chains, and gemini structures were beneficial to decreasing the hydrophilicity of lignite. Structures to be avoided included anionic types, branches, aromatic rings, and glucoside. The adsorbed surfactant layer covered the oxygen containing functional groups on the surface of the lignite, and also blocked lignite pores to reduce the storage space of water, effectively reducing the hydrophilicity of the lignite. The contribution of the coverage of oxygen-containing functional groups was found to be more significant. In addition, we demonstrated the consistency between moisture readsorption and wetting heat in terms of presenting hydrophilicity of lignite and their differences were also discussed. Our results provide a reference for selecting an appropriate strategy and further developing the application of surfactants to decrease lignite hydrophilicity.

Cooperative Effects in Surfactant Adsorption Layers at Water/Alkane Interfaces

In the present work, the properties of dodecyl dimethyl phosphine oxide (C12DMPO) at the water/decane interface are studied and compared with those obtained earlier at the interface to hexane. To simulate the interfacial behavior, a two-component thermodynamic model is proposed, which combines the equation of state and Frumkin isotherm for decane with the reorientation model involving the intrinsic compressibility for the surfactant. In this approach, the surface activity of decane is governed by its interaction with C12DMPO. The theory predicts the influence of decane on the decrease of the surface tension at a very low surfactant concentration for realistic values of the ratio of the adsorbed amounts of decane and surfactant. The surfactant’s distribution coefficient between the aqueous and decane phases is determined. Two types of adsorption systems were used: a decane drop immersed into the C12DMPO aqueous solution, and a water drop immersed into the C12DMPO solution in decane. To determine the distribution coefficient, a method based on the analysis of the transfer of C12DMPO between water and decane is also employed.

Formation of carboxymethylchitosan/gemini surfactant adsorption layers at the air/water interface: Effects of association in the bulk

The surface properties of mixed solutions containing an anionic polyelectrolyte, carboxymethylchitosan (CMCH), and a cationic gemini surfactant, 1,2-bis(dodecyldimethlyammonio)hexane dibromide (C12C6C12), were studied by measuring the surface tension and the dynamic surface elasticity. The association behaviors in the solutions were also measured by fluorescence probe technique. The results showed that the adsorption layer transformed from pure elastic 2D layer to visco-elastic 3D layer with increase in surfactant concentration. The microparticles in the 3D layer were adsorbed from the adjacent bulk to the surface but not formed directly in the surface layer as it was sometimes assumed in other polyelectrolyte/surfactant systems. The stress relaxation mechanism were supposed to be the mass exchange between the unstructured thinner film surrounding the microparticles and the adjacent bulk during the surface compression or expansion. These surface properties of CMCH/C12C6C12 solutions were influenced strongly by the association in the bulk solution.

Simple Method for Rheological Determination of Surfactant Layer Thickness, Adsorbed on Soft Rubber Particles.

Natural rubber latex is a colloidal suspension of particles, which is very important for many industrial applications. These latex particles are not only polydispersed but also very soft and deformable, which makes the prediction of rheological properties much difficult. Herein, the rheology of natural rubber latex has been studied at high particle concentrations, analyzing the effects of surfactant addition on colloidal stability. A hydrophobically modified inulin surfactant (INUTEC NRA) was selected for this study since previous works had shown that this inulin surfactant imparts good colloidal stability to polystyrene latex particles. The most important objective was studying the influence of the surfactant on the particle adsorbed layer and determining the thickness of the adsorbed surfactant layer. The results showed that the relative viscosity increased as a function of latex volume fraction, and this increase became extremely sharp as the volume fraction approached the maximum packing volume fraction, as expected. This variation in viscosity with the volume fraction has a complex behavior, which could not be analyzed using conventional models based on hard rigid spheres, such as Krieger-Dougherty (K-D) or Maron-Pierce (M-P). Herein, we describe a simple semiempirical method to determine the surfactant adsorbed layer thickness, based on the linear dependence of intrinsic viscosity with 1/(ϕmax - ϕ)2, where ϕ is the volume fraction of rubber particles and ϕmax is the maximum volume fraction at which viscosity tends to infinity. The difference in the maximum packing fraction, with and without the surfactant, allows the calculation of the adsorbed layer thickness, δ ≈ 2.8 nm, which is a good estimate for the thickness of surfactant molecules adsorbed on latex particles. This surfactant thickness has been confirmed by direct measurements using dynamic light scattering (DLS), which gave a value of 3.1 nm. Viscoelastic oscillatory measurements have also been performed, showing that natural rubber particle suspensions are predominantly elastic above ϕ = 0.63 latex volume fractions. The elastic modulus has been analyzed as a function of surfactant concentration, confirming that the stability of latex particles is mainly controlled by the surfactant concentration.

Influence of Mixed 6-Thioguanine-Nonionic Surfactant Adsorption Layers on Kinetics and Mechanism of Bi(III) Ion Electroreduction

The presence of mixed 6-thioguanine-nonionic surfactant adsorption layers affects the mechanism and kinetics of the irreversible Bi(III) ion electroreduction process in chlorates(VII). Tween 80 and Triton X-100 change the dynamics of the catalytic effects of 6-thioguanine on Bi(III) ion electroreduction with the tendency of inhibition. The mechanism of catalytic activity of 6-thioguanine is associated with formation of complexes under specific conditions which exist on the electrode surface. The effects of both 6TG and suitable surfactant mixture on the first electron transfer are much greater than those on the transition of other electrons. The Bi-6TG type complex plays the main role in the Bi-6-thioguanine-Tween 80 or Bi-6-thioguanine-Triton X-100 systems, as 6-thioguanine dominates in the formation of adsorption equilibria of the studied mixtures.Graphical The reaction path obtained for Bi(III) ion electroreduction showing active complexes Bi-6TG acting as intermediates in electron transfer and in the presence of surfactants.

Coalescence of Water Drops at an Oil–Water Interface Loaded with Microparticles and Surfactants

This work investigates the coalescence of water droplets settled on a water–oil interface in the presence of microparticles and surfactant. The successive stages of the coalescence process, including interstitial film formation, drainage, rupture, and retraction, are analyzed in detail. This leads us to distinguish between contrasted situations depending on the nature of the surfactant and its affinity with the microparticles. Hydrophilic particles have been previously shown to promote coalescence by means of a bridging mechanism. In that case, coalescence is a deterministic process that lasts the time required for the drainage to make the film thickness equal to the size of the particles. However, the present study shows how surfactants can totally change the effect of the particles upon coalescence. When surfactant both stabilizes the water–oil interface and adsorbs onto the particles, the bridging mechanism is inhibited and the coalescence becomes a random process. Since molecular forces between facing film interfaces are not attractive, thermal fluctuations are required to initiate the formation of a hole in the adsorbed surfactant layer. Provided the surfactant concentration in the bulk is large enough to ensure that the interfaces are close to saturation, the coalescence is delayed by a stochastic time interval and the drop coalescence becomes a Poisson process. These results shed a new light on the mechanisms of droplet coalescence in complex industrial applications where surfactant and particles are present, either purposely added or present as uncontrolled contaminants.

Observing the Effects of Temperature and Surface Roughness on Cetyltrimethylammonium Bromide Adsorption Using a Quartz‐Crystal Microbalance with Dissipation Monitoring

AbstractThe effects of temperature and surface roughness on the mass and viscoelasticity of an adsorbed surfactant layer were monitored using a quartz crystal microbalance with dissipation monitoring (QCM‐D). Adsorption isotherms at 30, 40, 50, and 60 °C and at two different roughnesses on gold were measured for cetyltrimethylammonium bromide (CTAB). All isotherms displayed an increase in mass and dissipation as surfactant concentration was increased to its critical micelle concentration (CMC). Above the CMC, adsorption reached a peak followed by a slight decrease to a plateau at the equilibrium adsorption value. As the temperature was increased, the adsorbed mass above the CMC decreased. The adsorbed mass decreased further by increasing substrate roughness, while the dissipation remained unchanged within experimental uncertainty. Dynamic adsorption experiments were also conducted at various temperatures for select concentrations above and below the CMC, providing evidence for the importance of different adsorption mechanisms as a function of both surfactant concentration and surface roughness.

Effect of Surfactants on the Reduction of Cadmium(II) Ions on Cadmium Electrode

The effect high molecular weight water-soluble surfactants with different functional groups have on the electroreduction of cadmium(II) ions on a cadmium electrode in various electrolytes is studied. A copolymer of methacryloylaminophenol with acrylic acid, a leather waste hydrolyzate, and a copolymer of monoethanolamine with vinyl ether acetate are used as surfactants. The electrolytes that are used are 1 M KCl, KBr, KNO3, HCOONa, NH2SO3H, 0.5 M Na2SO4, and 0.35 M Na3C6H5O7 · 2H2O. It is shown that in 1.0 M KCl or KBr solutions, there is no inhibition of the electroreduction of cadmium(II) ions by the adsorption layers of surfactants. It is found that the inhibitory effect of polymers on the electroreduction of cadmium(II) ions in different background electrolytes increases in the order KCl > KBr > KNO3 > NH2SO3H > Na2SO4 > Na3C6H5O7 · 2H2O > HCOONa.

Dilational interfacial rheology of tridecyl dimethyl phosphine oxide adsorption layers at the water/hexane interface

The dilational visco-elasticity of surfactant adsorption layers was measured at low frequencies by the drop profile analysis tensiometry using oscillating drops. As the studied non-ionic surfactant C13DMPO (tridecyl dimethyl phosphine oxide) is soluble in water and in hexane, the partitioning of the surfactant between the two solvents had to be taken into consideration. The diffusion controlled exchange of matter theory was generalized in order to take into consideration the curvature of the interface, the diffusional transport in both adjacent bulk phases as well as the transfer across the liquid interface. Using two configurations, i.e. water drop in hexane and hexane drop in water, it is shown that the frequency dependence of the visco-elasticity modulus and the phase angle can be well described when the correct partition coefficient is applied. The surface activity of the selected surfactant C13DMPO is optimum to demonstrate the impact of matter transfer across the interface on the dilational visco-elasticity of interfacial adsorption layers of non-ionic surfactants.

Ion-Specific Effects on Equilibrium Adsorption Layers of Ionic Surfactants

This review article reports on the effect of the counter-ions on the ionic surfactant adsorption layer and its relation to the stability of foams and emulsions. The adsorption theory of Davies about the ionic surfactant monolayer was revisited and it is shown how to account for the type of the counter-ions. The experimental validation of this theory on thin liquid films was shown as well, thus explaining the effect of Hofmeister. However their effect on foams and emulsions is more complex. Furthermore, it is shown how the counter-ions affect in complex way the stability of foams and emulsions via the surfactant adsorption layer in the light of the newest theory. To elucidate the nature of this effect further investigation is called for.

Molecular dynamics study of the effect of inorganic salts on the monolayer of four surfactants at the oil/water interface

The molecular dynamics (MD) simulation method was used to simulate the aggregation of four types of surfactants at the oil/water interface. The effect of different cations such as Na+, Mg2+ and Ca2+ was compared. The results show that the interaction between different types and concentrations of cationic and head group of surfactants causes the surfactant adsorption layer to bend and changes the aggregation morphology of the micelles. The radial distribution function (RDF) of the surfactant head groups with water molecules and cations is calculated. The calculated results show that it exists a chemical hydration layer and a physical hydration layer between the surfactant head groups and the water molecules. Cation has different degrees of impact, thus changes the original hydration structure. Nonionic and zwitterion surfactants have good salt resistance. Potential of Mean Force (PMF) was used to analyze the energy change when the cation interacted with the polar head. The nonionic and zwitterion surfactants are determined to have a good oil displacement effect even under the conditions of high calcium-magnesium mineralization. The present results could help in choosing surfactants used in oil/water with inorganic salts.

РОЗРОБКА РЕЦЕПТУРИ ЕМУЛЬСІЙНОГО КОСМЕТИЧНОГО ПРОДУКТУ НА ОСНОВІ КОЛОЇДНИХ ЗАКОНОМІРНОСТЕЙ

Urgency of the research. Synthesis of new emulsion cosmetic products with given consumer characteristics depends on colloidal and chemical properties of both source components and finished products. In this case, particular attention is paid to the problems of the stability of cosmetic emulsions and the selection of effective emulsifier. Therefore, the de-velopment of a scientifically grounded approach to the creation of new formulations requires knowledge of the colloidal and chemical properties of both the source components and the final cosmetic emulsions. Target setting. Practice shows that as stabilizers of cosmetic emulsions, surface-active substances and their mixtures are most often used to obtain ready-made compositions with given properties. At the same time, the recipes of emulsion cos-metics are based on numerous experimental data, which greatly complicates and costs cosmetic production. Actual scientific researches and issues analysis. The latest open access publications were considered. Uninvestigated parts of general matters defining. Establishment of the basic colloid-chemical laws of the synthesis of cosmetic emulsions and the identification of the relationship between the colloid-chemical properties of the initial compo-nents and the characteristics of the final composition. The research objective. Selection of a stabilizer, consisting of a mixture of surfactants; determination of the main col-loid-chemical properties of surfactants and their mixtures, as well as the behavior of individual surfactants and their mix-tures at the interface between the phases of the liquid-liquid. The statement of basic materials. Using the surface tension data, an oil phase is selected at the interface between oil and water phases. According to the method of weight-volume of the drop, the data of the optimal ratio of emulsion stabilizers are determined. The obtained emulsions were investigated for colloidal stability. Conclusions. Exhausted method for obtaining a direct emulsion stabilized by a mixture of surface-active substances. The values of the parameters of adsorption layers of water-soluble surfactants at the interface between the solution-butter phases are determined. An optimal concentration of a mixture of surface-active substances has been established, which al-lows achieving the maximum stabilizing effect. It is determined that in order to obtain emulsions, stable for several months, the introduction of additional structural formulation, which will be the subject of our further research, is required.

The effect of surfactant adsorption on surface wettability and flow resistance in slit nanopore: A molecular dynamics study

Hypothesis: Due to large surface/volume ratio, fluid flow resistance in nanopores is affected dramatically by surfactants adsorption, which dictates wettability and friction. Surfactants with different aggregated morphology and molecular alignment at solid/water interface are expected to affect friction and mobility of surfactant adsorption layer, both of which should be possible to contribute to surfactant drag reduction mechanism in nanopores.Simulations: Molecular dynamics (MD) simulations were adopted to study the morphology of the adsorption layer of different types of surfactants on negatively charged hydrophilic silica surface and their effect on flow resistance in slit nanopores.Findings: Flow resistance differs as surfactant adsorption morphologies vary. Adsorption layer composed of hemimicelles with “head on” orientation in low adsorption amount exhibits low flow resistance. As adsorption amount increases, adsorption layer evolves into the double layer in which less polar surfactant composition is found to be beneficial for improving hydrophobicity of pore wall and interfacial water diffusion. More ordered and tight intermolecular packing and high mobility of the adsorption layer are found to be propitious to reduce the flow friction.

Dynamics simulation of disperse systems in the presence of a structure-related mechanical barrier resulting from surfactant adsorption

A computer model has been developed to refine the notions of the kinetics of structural transformations in surfactant-modified disperse systems, the mechanism of the influence of adsorption layers on viscosity, conditions of aggregation, and evolution of nonuniformities in microstructures. Classical concepts of the structure-related mechanical barrier providing disperse systems with stability to aggregation, as well as the criterion of adsorption-layer breakdown upon interparticle collisions under dynamic conditions, have been used. It has been shown that adsorption-layer breakdown under dynamic conditions may lead to the appearance of an extreme in the viscosity curve of a disperse system. The combined effect of additives of surfactants with different molecular masses successively added to the systems has been studied via taking into account the influence of surfactant adsorption layers on the dynamics of contact interactions. The simulation results make it possible to optimize the regulation of structure-related rheological properties of dispersions so as to decrease their apparent viscosity with a simultaneous increase in the uniformity of the structure.

Surface rheology and its relation to foam stability in solutions of sodium decyl sulfate

The anionic surfactant sodium decyl sulfate (SDeS) at concentrations below its critical micellar concentration (cmc) was studied in a surface chemically purified state at the air–water interface in terms of its static and dynamic interfacial properties. Equilibrium surface tension was determined using a pendant drop tensiometer. An oscillating bubble capillary pressure tensiometer allowed accessing the surface dilatational properties of the surfactant's adsorption layers in a frequency range from 2 to 500Hz. The estimation of single foam lamella stability was obtained from visual observation of films formed within a rectangular glass frame in a saturated atmosphere. Upon increasing surfactant concentration, the foam lamellae were found to rupture at prolonged lifetimes. The dramatic difference in foam stability goes along with a pronounced transition from a surface elastic to a surface visco-elastic state of the adsorption layers. These findings were indicative for a correlation between foam lamella stability and surface viscoelasticity also for this model surfactant. These results may be of importance to further shed light on the processes governing foam and foam lamella stability.

Dilational rheology of different globular protein with imidazolium-based ionic liquid surfactant adsorption layer at the decane/water interface

This contribution is concerned with the imidazolium-based ionic liquid surfactant being considered potential amphiphilic molecules. The interfacial dilational rheology of solutions of globular proteins (lysozyme and bovine serum albumin (BSA)) with imidazolium-based ionic liquid surfactant (1-dodecyl-3-methyl imidazolium bromide ([C12mim]Br)) have been measured as a function of the surfactant concentration, interface lifetime and interfacial pressure. The dynamic interfacial dilational modulus of lysozyme/[C12mim]Br solutions are always monotonous, but that of the BSA/[C12mim]Br solutions become nonmonotonous indicating the destruction of the protein structure. One can assume that some lysozyme molecules desorb from interface due to competitive of free [C12mim]Br molecules for lysozyme/[C12mim]Br solution with [C12mim]Br concentration increasing, however, BSA molecules unfolding of compact globule have been subject to conformational changes so that it can give space for more [C12mim]Br molecules to co-adsorb. This aimed to provide more theoretical information for practical applications of imidazolium-based ionic liquid surfactant.

On the Mechanism of Drop Self-Shaping in Cooled Emulsions.

Two recent studies (Denkov et al., Nature 2015, 528, 392 and Guttman et al. Proc. Natl. Acad. Sci. U.S.A.2016, 113, 493) demonstrated that micrometer-sized n-alkane drops, dispersed in aqueous surfactant solutions, can break their spherical symmetry upon cooling and self-shape into a variety of regular shapes, such as fluid polyhedra, platelet-shaped hexagons, triangles, rhomboids, toroids, and submicrometer-diameter fibers. In the first study, the observed phenomenon was explained by a mechanism involving the formation of interfacial multilayer of self-assembled alkane molecules in the so-called rotator phases, templated by the frozen surfactant adsorption layer. Such phases are known to form in alkane droplets under similar conditions and are sufficiently strong to deform the droplets against the capillary pressure of a finite interfacial tension of several mN/m. The authors of the second study proposed a different explanation, namely, that the oil-water interfacial tension becomes ultralow upon cooling, which allows for surface extension and drop deformation at negligible energy penalty. To reveal which of these mechanisms is operative, we measure in the current study the temperature dependence of the interfacial tensions of several systems undergoing such drop-shape transitions. Our results unambiguously show that drop self-shaping is not related to ultralow oil-water interfacial tension, as proposed by Guttmann et al. These results support the mechanism proposed by Denkov et al., which implies that the large bending moment, required to deform an oil-water interface with an interfacial tension of 5 to 10 mN/m, is generated by an interfacial multilayer of self-assembled alkane molecules.

Adsorption of Cationic SA on Polyester Fiber Surface and its Influence on the Electrokinetic Potential

from a study of the adsorption of the cationic surfactant (SA) catamine AB from aqueous solutions onto the surface of polyester fibers are reported. It was found that a bimolecular layer was formed after adsorption of this SA. The SA molecules in the first adsorbed layer reacted with polyester polar groups to form an interpolymer complex. A specific adsorption potential, i.e., intermolecular interaction of SA hydrocarbon groups with fiber hydrophobic sections, was also apparent. The second adsorption layer was formed exclusively via reaction of hydrocarbon radicals of the first and second adsorbed layers. The effect of catamine-AB adsorption on the polyester-fiber electrokinetic surface potential was investigated. It was found that the negative electrokinetic potential decreased as the adsorbed SA layer formed on the fiber surface. The isoelectric surface state was observed at a catamine concentration of ~5·10–2 g/L, after which the fiber became overcharged. This indicated that the SA adsorbed to form a bilayer structure.

Sulfonated methyl esters, linear alkylbenzene sulfonates and their mixed solutions: Micellization and effect of Ca2+ ions

Here, we compare the properties of sulfonated methyl esters of fatty acids (SME) and linear alkylbenzene sulfonate (LAS) with respect to the effect of calcium ions on their surface tension and the effect of their mixing on the critical micelle concentration (CMC). The theoretical interpretation of surface tension isotherms obtained in the presence of NaCl and CaCl2 allowed us to determine the parameters that characterize the surfactant adsorption layers and counterion binding. The excluded area per molecule in the adsorption layer is the same for SME and LAS, and is determined by the cross-sectional area of the sulfonate headgroup. The binding energy of Na+ ions to the headgroups of SME and LAS is also the same. However, the binding energy of the Ca2+ ion to the headgroup of LAS is considerably greater than that of SME in agreement with the circumstance that LAS is precipitated by hard water. In contrast, the binding energy of the Ca2+ ion to the headgroup of SME is lower even than that of Na+, in accord with the reputation of SME as one of the most hard-water tolerant surfactants. The dependencies of the CMC on the composition of binary mixed surfactant solutions reveal that C14-SME and C16-SME exhibit ideal mixing; C14-SME and LAS – slightly synergistic mixing, whereas C16-SME and LAS – antagonistic mixing due to hydrocarbon-chain mismatch. The micellization in mixed solutions of SME and cocamidopropyl betaine has been also investigated. The results in the present study allow prediction of the surface tension of solutions of SME and LAS in the presence of Na+ and Ca2+ ions at various concentrations; contribute for a better understanding of the different tolerance of SME and LAS to hard water, and quantify the effect of their mixing on the CMC.