Surfactant-water Systems Research Articles

Liquids with internal surfaces at and out of equilibrium: the homogeneity index

In this article, we discuss the application of the homogeneity index to the study of the morphology of the binary mixtures (two homopolymers) undergoing phase separation below the convolute (critical) point. The homogeneity index is a measure of how homogeneous, in terms of the local curvatures, is the interface, which is formed inside the system in the process of phase separation. In this article, we will compare the value of the homogeneity index for the phase separating binary mixture with the one for magnetic systems undergoing phase ordering and also to the homogeneity index known for various bicontinuous phases observed at equilibrium in the mixtures of surfactant-water systems. We will show that the homogeneity index is probably the best tool (most sensitive) for the study of the dynamic scaling in the ordering or phase separating systems.

Phases and structures of a polyion–surfactant ion complex salt in aqueous mixtures: cationic hydroxyethyl cellulose with dodecylsulfate counterions

A polyion–surfactant ion complex salt, cat-HECDS, has been synthesised, consisting of cationic hydroxyethyl cellulose with dodecylsulfate counterions. Ternary phase diagrams have been established for aqueous mixtures of cat-HECDS with either the conventional surfactant NaDS or the polyelectrolyte cat-HECCl. Such mixtures represent the simplest possible aqueous mixtures of oppositely charged polymer and surfactant where the proportions of polyion and surfactant ion may be varied. Phases and structures were investigated by visual inspection through crossed polarisers and by small-angle X-ray scattering (SAXS). The pure complex salt cat-HECDS was insoluble in water, but it could absorb up to 60 wt.% water. No crystalline order was detected at any water content. Dissolution of the complex salt in water occurred if sufficient amounts of either surfactant or polyelectrolyte was added. A smaller excess of surfactant (50% by charge) than polyelectrolyte (100% by charge) was needed to dissolve the complex salt in the dilute region. The efficiency of excess NaDS to dissolve the complex salt was attributed to hydrophobic interactions between the surfactant and the cat-HEC backbone. The free surfactant concentration at the onset of dissolution was in good agreement with the critical association concentration observed in previous gel experiments. The investigated phase diagrams were dominated by a large isotropic phase containing micellar surfactant aggregates without long-range order. The micellar aggregation number varied from ∼20 for aqueous cat-HECDS to ∼80 for mixtures rich in NaDS. A small fraction of added complex salt was enough to destroy the hexagonal phase formed in binary mixtures of NaDS and water. The absence of liquid crystalline phases containing significant amounts of complex salt was attributed to the stiff character of the polyion and its low charge density. In a ternary complex salt–surfactant–water system studied previously, where the complex salt contained a flexible polyion with a high charge density, liquid crystalline phases were found at all proportions of complex salt.

Formation and dissociation studies for optimizing the uptake of methane by methane hydrates

Characteristics such as temperature and pressure profiles for methane hydrate formation and dissociation in pure water, simulated seawater, and water–surfactant systems have been established. A hysteresis effect has been observed for repeated formation–dissociation cycles of the same methane–water system. In an attempt to maximize the uptake of methane during methane hydrate formation, the addition of sodium dodecyl sulfate provided methane uptake of over 97% of the theoretical maximum uptake. Additional surfactants were tested for their ability to enhance the uptake of methane for hydrate formation. Successful demonstration of efficient methane storage using hydrate formation enhanced by addition of surfactants could provide a safe, low-cost alternative method for storage of natural gas at remote locations.

The physics of surfactant dissolution.

We have examined the early stages of surfactant dissolution and mesophase formation using a dimer-solvent model with phase behaviour representative of surfactant-water systems. We use an orientational order parameter to characterize systematically the appearance of mesophases. We find the process is diffusion controlled, and the appearance of mesophases is governed adiabatically by the equilibrium phase diagram from the earliest point at which the orientational order parameter can reliably distinguish between mesophases, when only a few repeat spacings of the mesophase microstructures are present. In real systems, such a stage would correspond to times of the order of a few microseconds after the initial contact.

A Defective Lamellar Phase in a Nonionic Surfactant Water System Studied by NMR Methods

Lamellar phases of some surfactant water system are not infinite, continuous lamellar planes but several experimental findings showed that they contain water-filled defects with highly curved edges. Here, the polydomain lamellar phase of the pentaethylene glycol dodecyl ether(C 12 E 5 )/decane/water system has been studied by 1 H-NMR pulsed field gradient experiments (PGSE) and 2 H-NMR line shapes of D 2 O, at a constant surfactant (S) to oil (O) weight ratio of 51.8/48.2. Within the lamellar phase of this system, which was observed at S+O weight fraction from 5 to 82 wt%, three types of bilayer organisation have been found. At low surfactant+oil concentrations, <45wt% S+O, the lamellar phase consists of a stack of flat parallel bilayers while within a intermediate-concentration regime water-filled bilayers exist, as demonstrated by the presence of three-dimensional water diffusion. At concentration higher than 68 wt% S+O this defected lamellar phase oriented in the magnetic field, giving a mono-domain structure.

Dye Method to Identify the Types of Cubic Phases

Cubic phases formed in surfactant or copolymer solutions are optically-isotropic and highly viscous liquid crystals. They are mainly categorized to four types; normal micellar discontinuous (I1), reverse micellar discontinous (I2), normal bicontinuous (V1), reverse bicontinuous (V2) cubic phases. We used both water- and oil-soluble dye solutions to specify the type of cubic phase by a simple dyeing method. Water-soluble dye (Tartrazine) colors I1 phase, whereas it remains on the top of I2 phase. Oil-soluble dye (Sudan III) shows the opposite phenomena. Both dyes do color the V1 and V2 phases in binary water-surfactant systems. In the presence of oil, the water-soluble dye colors the V1 phase faster than the V2 phase. The oil-soluble dye shows the opposite rate of dyeing to bicontinuous cubic phases.

Raman spectroscopic study of temperature dependence of water structure in aqueous solutions of a poly(oxyethylene) surfactant

The temperature dependence of the water structure in aqueous solutions of a poly(oxyethylene) surfactant C12E5 was examined at concentrations 0, 20, 30, 45, 70 and 90wt% by Raman spectroscopy of the O–H stretching band. The ratio of the intensities of the component around 3200cm−1 (the collective in-phase O–H stretching vibrations of bonded aggregates) to the component around 3400cm−1 (the O–H stretches in which the phase relations are lost) was monitored in the temperature range from 0 to 39°C. The results show that the speed of the thermal destruction of the H-bond network increases as the concentration increases from 0 to 45wt%. This change is attributed to the existence of a substantial amount of water in the system that takes part in the hydrophobic hydration of the poly(oxyethylene) headgroups, despite their predominantly hydrophilic character. The conclusion that this kind of water, which is known to have restricted mobility, plays an important role in the surfactant–water systems is consistent with the high viscosity of the liquid crystalline phases.

Lattice-Boltzmann simulations of self-assembly of a binary water-surfactant system into ordered bicontinuous cubic and lamellar phases.

We used our recently developed mesoscale amphiphilic lattice-Boltzmann method (Nekovee, M.; Coveney, P. V.; Chen, H.; Boghosian, B. M. Phys. Rev. E 2000, 62, 8282-8894) to investigate the dynamics of self-assembly of the bicontinuous cubic phase in a binary water-surfactant system, and the transition from the lamellar structure to a bicontinuous cubic phase. Our study provides insight into how such structures emerge as a result of competing molecular interactions between water and amphiphiles and among amphiphilic molecules themselves, and represents the first application of any lattice-Boltzmann model to amphiphilic systems in three dimensions.

Structure and dynamics of concentrated micellar phase in nonionic surfactant-water systems

Abstract Dynamic light scattering has been measured on aqueous solutions of a nonionic surfactant C14E6 (CnEm represents a chemical formula CnE2n+1(OC2H4)mOH). In the time correlation function of the scattered field for semidilute solutions were wormlike micelles are entangled, we have found the so-called slow mode in addition to the diffusion mode. Concentration and temperature dependences of the relaxation time of the slow mode (τs) are strongly correlated with those of the surfactant self-diffusion coefficient (D), suggesting that self-diffusion and structural relaxation are dominated by the same kinetic process. These results are consistent with our previous study on the C16E7 system. In order to refine the kinetic model, we have compared τs and D quantitatively based on our diffusion model reported before where intramicellar diffusion and intermicellar migration are taken into account. Static light scattering measurements have been performed to estimate one of parameters included in this model. It has been suggested that entangled micelles form a transient connection whose lifetime is of the order of 10−3 s, depending on concentration and temperature, and that surfactant molecules migrate to another micelle through such a transient connection.

Phase studies of surfactant–water systems

Significant advances have been made in establishing phase behavior of a number of nonionic, cationic, anionic, catanionic and fluorinated surfactants in water. An interest in phase equilibria existing at sub-ambient temperatures is developing. The study of cubic, intermediate, defective lamellar and sponge phases is an active field of research at present. Further work is needed in exploring thermodynamic stability of rigid nanodisks and densely packed vesicles. Colloidal aspects, thermodynamic and volumetric properties of the surfactant-containing systems deserve special attention.

Phase Behavior and Phase Structure of Protein–Surfactant–Water Systems

Phase behavior of oppositely charged ovalbumin–DOTAC and BSA–DOTAC, and similarly charged ovalbumin–SDS, BSA–SDS, lysozyme–DOTAC, and BLG–SDS systems within the concentration range of 20 wt% of both protein and surfactant are examined in water. Aqueous solutions of ovalbumin yield, in succession, precipitation, gel, and solution with increased addition of the surfactant dodecyltrimethylammonium chloride (DOTAC). The stability range of each region is determined. Both isotropic and anisotropic gels are detected. Solutions of bovine serum albumin (BSA) form only a solution phase with oppositely charged DOTAC. One solution phase is also obtained with all similarly charged protein–surfactant systems except the BLG–SDS–water system, which produces a gel phase in addition to a large solution phase. 2H NMR longitudinal (R1) and transverse (R2) relaxation rates are determined in solution and gel by following the behavior of selectively deuterated surfactant at the α-methylene group next to the surfactant head group for the oppositely charged systems ovalbumin–DOTAC and BSA–DOTAC. Large R2-values proved the existence of large protein–surfactant aggregates in both systems.

Rheological behaviour of a lamellar liquid crystalline surfactant–water system

The rheological behaviour of a lamellar liquid crystalline surfactant–water system was investigated using a Haake RS-100 viscometer. The repeat distance of lamellae as a function of surfactant concentration and temperature was measured by small-angle X-ray scattering. The rheological characteristics were measured at different temperatures with systems containing surfactant in different concentrations. The frequency-dependent storage and loss modulus were found to be characteristic to the lamellar phase in the linear viscoelastic region.The results are analysed on the basis of Jones–McLeish slip-plane theory. Trends of the fitted constants are discussed based on the general knowledge on the interactions in dispersions stabilized by non-ionic surfactants, and the structure of lamellar liquid crystalline samples. Time-dependent compliance was also measured. The instantaneous elasticity measured in the creep tests was compared with that predicted from oscillatory tests. Burger's model was used to describe the time-dependent compliance.Viscosity measurements in the non-linear region were also done. A modified Carreau equation is used to describe the viscosity versus shear rate curves. The changes in sample under shear is described briefly.

Modeling the Dynamics of Amphiphilic Fluids

We show how a lattice-Boltzmann approach can be extended to ternary fluid mixtures with the aim of modeling the diverse behavior of oil–water-surfactant systems. We model the mixture using a Ginzburg–Landau free energy with two scalar order parameters which allows us to define a lattice-Boltzmann scheme in the spirit of the Cahn–Hilliard approach to nonequilibrium dynamics. Results are presented for the spontaneous emulsification of an oil–water droplet and for spinodal decomposition in the presence of a surfactant.

Studies of surfactant/water systems near the critical micellar concentration using thermal lens spectroscopy

A novel application of photothermal spectroscopy to the study of surfactant-water systems near the critical micellar concentration is reported. The thermal lens signal was induced by a slightly soluble dye and was measured with a dual-beam thermal lens spectrometer. For the two surfactants considered: nonyl phenol and Triton X-100, sharp variations of the thermal lens signal were observed at the critical micellar concentration (CMC), namely an increase for nonyl phenol and a decrease for triton X-100. These effects are arguably related to micelle formation. Our work serves as an initial assessment of the potential of the technique for the study of disperse systems of a higher complexity or dark systems where conventional techniques are impossible to apply.

Liquid crystalline surfactant phases in chemical applications

The importance of lyotropic liquid crystalline structures is shown for two selected surfactant applications,i.e. cosmetics and detergency. The properties of lyotropic liquid crystals are demonstrated for binary surfactant–water systems, ternary surfactant–oil–water systems and multicomponent systems. Detailed knowledge of the phase behavior is crucial for tailor-made product development.

Changes in form and relative stability of micelles in multicomponent systems

Calculations of the relative stability of different micelle forms in surfactant multicomponent (more than two) systems were performed on the basis of the surfactant parameter model. The results show that some particular micelle forms, that are of little relative stability in a binary water-surfactant system, are strongly stabilized by the presence of cosurfactants whose molecules fit best in micelle zones of distinct curvatures.

Phase Transition Behavior of Cationic Surfactant-Water Systems Studied by Nanosecond Fluorescence Anisotropy.

The phase transition behavior of cationic surfactants with a double-chain (Arquad 2HT and Arquad 2O) in dilute aqueous solution is studied from -30 to 70°C by time resolved fluorescence anisotropy. The phase transitions of a coagel-gel and a gel-liquid crystal in the Arquad 2HT system are observed to take place at 36 and 42°C, as has also been noted for the dioctadecyldimethylammonium chloride-water system. The coagel-gel phase transition causes the distance separating the alkyl chains of Arquad 2HT to change, but this has no effect on chain fluctuation. Arquad 2O is assumed to be a liquid crystalline state at temperatures above -30°C.

Lamellar Phases in Contact with the Lower Consolute Loop of Ionic Surfactant-Water Systems

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLamellar Phases in Contact with the Lower Consolute Loop of Ionic Surfactant-Water SystemsA. M. Smith, M. C. Holmes, A. Pitt, W. Harrison, and G. J. T. TiddyCite this: Langmuir 1995, 11, 11, 4202–4204Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/la00011a006RIGHTS & PERMISSIONSArticle Views104Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (445 KB) Get e-Alerts Get e-Alerts

Thermodynamic study of the micellar solution — Solid surfactant equilibrium

The temperature-composition dependence along the Krafft boundary in surfactant-water systems and the effect of the third component on the surfactant precipitation temperature are analyzed on the basis of strict thermodynamic relationships and using approximate models (the ideal monodispersed micellar solution approximation, the pseudo phase separation model). As it follows from the consideration a substantial decrease in the surfactant precipitation temperature (ΔT) may be observed on addition of light amphiphilic substances forming mixed micelles with the basic surfactant, the distribution coefficient between the micelles and the aqueous surroundings being an important characteristic of an additive. Regularities in the dependence of the ΔT-effects on the third component chemical nature and on the mixture composition are discussed. The model approaches are illustrated in application to the N-dodecanoyl-N-methylglycamine-water system and for the system containing n-butanol as the third component. For the ternary system the concentration dependence of the alcohol activity coefficient in the aqueous pseudo phase was taken into account with the help of the UNIFAC model, this dependence influencing seriously the calculated results. The estimated ΔT-effects are in a satisfactory agreement with the experimental data, an information on the mixed micelles composition is drawn from the calculations.

Phase behaviour and structure in a non-ionic surfactant–oil–water mixture

A section of the composition–temperature phase prism of a ternary non-ionic surfactant–water–oil system defined by a constant surfactant to oil ratio has been investigated. The structural sequence of normal spheres to planar bilayers, via cylinders, is observed as a function of decreasing water concentration at fixed temperature. As a function of increasing temperature at fixed surfactant and oil concentration, we note the commonly observed reversal in mean curvature of the polar/apolar interface. The mean curvature progressively alters from positive values in the low-temperature microemulsion phase to negative mean curvature in the high-temperature L3 phase, with an intermediate lamellar phase where the mean curvature passes through zero. The phase diagram of this section is similar to that of the binary surfactant–water system. The average area per surfactant at the polar/apolar interface is 46 ± 2 A2. A micellar cubic phase is observed between the microemulsion and the hexagonal phase while no bicontinuous cubic phase is observed.