Properties Of Aqueous Surfactant Solutions Research Articles

Analysis of the micellar properties of surfactants dodecyl trimethylammonium bromide and dodecyl trimethylammonium chloride in aqueous ionic liquids solution

Understanding the influence of various additives on the properties of aqueous surfactant solutions is profoundly significant because of numerous applications of surfactant-based frameworks. Thus, the aggregation behavior of conventional cationic surfactants dodecyl trimethylammonium bromide (DTAB) and dodecyl trimethylammonium chloride (DTAC) has been investigated in the absence and presence of (0.05, 0.10, and 0.15) wt.% ionic liquids (ILs) 1-propyl-3-methylimidazolium bromide [C3mim][Br] and 1-butyl-3-methylimidazolium bromide [C4mim][Br] in aqueous medium at different temperatures (298.15, 303.15, and 308.15) K. The values of critical micelle concentration (CMC) have been evaluated for various IL/surfactant systems by employing three different techniques such as conductivity, fluorescence, and UV–VIS spectroscopy. The thermodynamic parameters of micellization have been ascertained utilizing these CMC values, determined by various techniques. Thermodynamic parameters like standard free energy, standard enthalpy, and standard entropy of micellization were examined in terms of driving force behind the process of micellization. These parameters revealed that the addition of ILs modifies the aggregation properties of DTAB and DTAC.

Effect of the Janus Amphiphilic Wall on the Viscosity Behavior of Aqueous Surfactant Solutions

The effects of the chemical nature of an interface are one of the key parameters which can affect self-assembly and rheological behavior. To date, several studies have reported self-assembled structures and rheological behaviors in the development of various functional materials. In this study, we investigated the self-assembly and viscosity behavior of aqueous surfactant solutions confined in three types of Janus amphiphilic nanotubes (JANTs), which have two, four, and eight sequential domains, respectively, using molecular simulation. We found that the viscosity behavior depends on the surfactant concentration and the chemical nature of the wall surface. For instance, although the concentration levels of the surfactants are the same (c = 10%), completely different viscosity behaviors were observed in the two sequential domains (Newtonian-like) and the four and eight sequential domains (strong shear-thinning) of the JANTs. Our simulations demonstrated how the rheological properties of aqueous surfactant solutions, including viscosity and velocity profiles, can be controlled by the chemical nature of the JANT wall surface, effect of confinement, and their self-assembly structures. Considering the foregoing, we hope that our study offers new knowledge on nanofluid systems.

Physico-chemical and dielectric relaxation studies of ionic surfactants in Time Domain Reflectometry (TDR)

The properties of aqueous surfactant solutions with external additives are extensively useful in surfactant-based systems. To study the dielectric relaxation studies of aqueous ionic surfactants (SDS, CTAB, DPC) and aqueous butanol, benzyl alcohol, aniline and tributylamine were carried out for different concentrations at 303k. Dielectric relaxation spectroscopy (DRS) is valuable for understanding the dynamic process mainly in micellar systems. Time domain dielectric data were obtained through HP54750A oscilloscope and TDR plug-in-module. The relaxation times were determined through the well-known Cole-Cole method. The superposition of two relaxation times gives the dielectric relaxation time obtained from the hydrated water molecule with rotations around the micelle, ions and another hydrophobic inner side of the micelle. Viscosity measurements were used to correlate the dielectric data. The Kirkwood correlation factor (g f ), effective Kirkwood correlation factor (g eff ), Bruggeman Factor (f B ), excess inverse relaxation time (1/τ) E , excess dielectric constant (e E ) and free energy of activation (ΔF t ) were also calculated. The effects of dielectric relaxation and viscous flow were interpreted and discussed.

Conductometric and tensiometric studies on the mixed micellar systems of surface-active ionic liquid and cationic surfactants in aqueous medium

Physicochemical properties of aqueous surfactant solutions can be suitably modified by the addition of room temperature surface-active ionic liquids (SAILs). As green solvents, these SAILs are used as the ideal additives for modifying the aqueous surfactant properties. Such mixed surfactant + SAIL systems in aqueous solutions find enormous applications in several technological fields. The changes in the micellar behavior of cationic surfactants cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) have been investigated in the presence of SAIL 1-decyl-3-methylimidazolium chloride [C10mim][Cl] employing conductometric and tensiometric methods. Micellar and interfacial parameters such as critical micelle concentration, cmc micellar mole fraction, X1, of component 1 (CPC/CPB), micellar interaction parameter, β, activity coefficients ƒ1 and ƒ2 of component 1 and component 2 (SAIL) in the mixed micelles, excess Gibbs free energy of micellization, ΔGex0, standard Gibbs free energy, ΔGmic0, enthalpy, ΔHmic0, and entropy, ΔSmic0 of micellization, surface excess concentration, Гmax, minimum surface area per molecule, Amin, and standard Gibbs free energy of adsorption ΔGad0 at the interface were evaluated. In addition, packing parameters of amphiphiles in the micelles, P, volume contribution of the hydrophobic chain, v, and its effective length, lC have also been evaluated for the pure and mixed systems. The interactions between CPC/CPB and SAIL in the mixtures are found to be non-ideal and synergistic, and that mixed micelles are richer in CPC/CPB monomers. Of the several interactive interactions, hydrophobic interaction seems to be dominant between the components of the mixed systems. Adsorption of SAIL molecules at air-solution interface is found to be richer in SAIL than CPC/CPB molecules, which is also supported by the higher negative ΔGad0 values than ΔGmic0values. The micelles/ mixed micelles formed have spherical geometry.

Properties of aqueous micellar solutions in the presence of ionic liquid

The physicochemical properties of aqueous surfactant solutions above their critical micelle concentrations (cmc) are governed by the micellar assemblies present within the solution. Due to their distinct structural features and properties, ionic liquids (ILs) can effectively and favorably modify the properties of aqueous micellar solutions. Effect of addition of a prototypical ‘hydrophobic’ IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), which exhibits only ∼2wt% miscibility in water at ambient conditions, on the properties of aqueous micellar solutions of four different surfactants, namely, nonionic triton X-100 (TX-100), anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS), and zwitterionic dodecylsulfobetaine (SB-12), is assessed. Surface tension, density, refractive index, and dynamic viscosity along with fluorescence probe-reported microfluidity of the four aqueous micellar solutions are investigated in the absence and presence of up to 5wt% [bmim][PF6]. Density and refractive index of aqueous micellar solutions increase linearly with wt% [bmim][PF6]. Increasing [bmim][PF6] results in decrease in surface tension of anionic/zwitterionic micellar solutions; on the contrary, the surface tension of nonionic TX-100 micellar solution increases. This is due to the negative adsorption exhibited by [bmim][PF6] within aqueous micellar TX-100 solution. There is an initial increase, in general, in the dynamic viscosity of the four micellar solutions as [bmim][PF6] is added; however, this increase is way more dramatic for SDBS. This is attributed to a drastic increase in the size of the micelles as a result of the presence of both [bmim][PF6]-SDBS electrostatic as well as cation-π interactions. Response from the microfluidity probe does not necessarily scale with the dynamic viscosity of the micellar solutions as [bmim][PF6] is added. The water penetration into the palisade layer of the [bmim][PF6]-added anionic micelles, where the microfluidity probe solubilizes, is the reason for this outcome. The aqueous micellar media is perturbed significantly in the presence of IL and the extent of the changes in the properties is contingent on the identity of the surfactant.

Automated system for measuring the surface dilational modulus of liquid–air interfaces

The surface dilational modulus is a crucial parameter for describing the rheological properties of aqueous surfactant solutions. These properties are important for many technological processes. The present paper describes a fully automated instrument based on the oscillating bubble technique. It works in the frequency range from 1 Hz to 500 Hz, where surfactant exchange dynamics governs the relaxation process. The originality of instrument design is the consistent combination of modern measurement technologies with advanced imaging and signal processing algorithms. Key steps on the way to reliable and precise measurements are the excitation of harmonic oscillation of the bubble, phase sensitive evaluation of the pressure response, adjustment and maintenance of the bubble shape to half sphere geometry for compensation of thermal drifts, contour tracing of the bubbles video images, removal of noise and artefacts within the image for improving the reliability of the measurement, and, in particular, a complex trigger scheme for the measurement of the oscillation amplitude, which may vary with frequency as a result of resonances. The corresponding automation and programming tasks are described in detail. Various programming strategies, such as the use of MATLAB® software and native C++ code are discussed. An advance in the measurement technique is demonstrated by a fully automated measurement. The instrument has the potential to mature into a standard technique in the fields of colloid and interface chemistry and provides a significant extension of the frequency range to established competing techniques and state-of-the-art devices based on the same measurement principle.

Interaction Between Ionic Liquids and Gemini Surfactant: A Detailed Investigation into the Role of Ionic Liquids in Modifying Properties of Aqueous Gemini Surfactant

AbstractTuning physicochemical properties of aqueous surfactant solutions comprised of normal or reverse micelles by external additives is of utmost importance due to the enormous application potential of surfactant‐based systems. Unusual and interesting properties of environmentally benign ionic liquids (IL) make them suitable candidates for this purpose. To understand and establish the role of IL in modifying properties of aqueous gemini surfactants, we studied the effect of the IL, 1‐hexyl‐3‐methylimidazolium bromide ([Hmim][Br]) and 1‐octyl‐3‐methylimidazolium bromide ([Omim][Br]) on the properties of the aqueous cationic gemini surfactant 1,6‐hexanediyl‐α,ω‐bis(dimethyltetradecyl)ammonium bromide (14‐6‐14,2Br−). The behavioral changes were investigated by measuring the critical micelle concentration (CMC) using electrical conductance, surface tension, dye solubilization and fluorescence probe measurements at 298.15 K. It was observed that the CMC of 14‐6‐14,2Br− gemini surfactant decreases with addition of IL, thus favoring the micellization process. An increase in micellar size was observed at lower IL concentration using dynamic light scattering, with a decrease in aggregation number (Nagg) determined from fluorescence probe quenching measurements. It is noteworthy that the extent of modulation of the micellar properties is different for both the IL due to their structural differences. IL behave like electrolytes at lower concentrations and cosurfactants at higher concentrations and form mixed micelles with the cationic gemini surfactant showing an increase in Nagg.

Unique role of ionic liquid [bmin][BF 4] during curcumin–surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF 4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF 4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (∼2-fold decrease) association with cationic surfactant solution.

Electrical potential modulation of dynamic film properties of aqueous surfactant solutions through a nanogap

The effect of external electrical potentials (EEPs) on aqueous surfactant films nanoconfined in a ball-plate configuration has been investigated by measuring the dynamic film thickness with an interferometer. Experimental results indicate that the film formation properties of the surfactant solutions in the nanogap under applied EEPs are strongly dependent on the interfacial adsorbed surfactant structure. Effective control over the film formation properties by applying EEPs depends on the signs of the charges on the solid surface and the surfactant headgroups, the surfactant concentration, and the magnitude of EEPs. Remarkable alterations of the film formation properties in the nanogap by EEPs can be observed except when the surface charge is the same in sign as the headgroups and the surfactant concentration is above the critical micelle concentration. Mechanisms of these phenomena have been discussed in this work.

Wetting of Single and Mixed Surfactant Solutions on Superhydrophobic Surfaces

Despite their potential application, the wetting properties of aqueous surfactant solutions on superhydrophobic (SH) solid surfaces have been rarely investigated. In this work single surfactant solutions and binary mixtures of non-ionic and ionic surfactants have been studied in contact with textured and non-textured surface coatings obtained utilizing nanoparticles and a fluorinated polymer. The role of the molecular structure and the concentration in the modification of the wetting properties has been observed both for individual species and mixtures. At supramicellar concentrations a significant decrease in the effectiveness of the mixed solution in wetting the SH surface in comparison to single ionic species has been found. A comparison with the same polymer coating, but in hydrophobic conditions, shows, on the contrary, that the wetting is slightly promoted by the mixture. The molecular size seems to play a positive role in wetting enhancement with the formation of more packed adsorption layer due to molecular penetration. The results of this work should be useful to design surfactant systems for a more effective wetting control.

Modifying Properties of Aqueous Cetyltrimethylammonium Bromide with External Additives: Ionic Liquid 1-Hexyl-3-methylimidazolium Bromide versus Cosurfactant n-Hexyltrimethylammonium Bromide

Understanding the effect of external additives on the properties of aqueous surfactant solutions is of utmost importance due to widespread applications of surfactant-based systems. Role of ionic liquids (ILs) in this regard may turn out to be crucial as these substances are known to possess unusual properties. To unambiguously understand and establish the role of ILs in modifying properties of aqueous surfactant systems, changes in the physicochemical properties of aqueous cetyltrimethylammonium bromide (CTAB) upon addition of an IL 1-hexyl-3-methylimidazolium bromide ([hmim][Br]) are compared with those when a cosurfactant n-hexyltrimethylammonium bromide (HeTAB) is added to aqueous CTAB. Important physicochemical properties, such as critical micelle concentration (cmc), aggregation number (N(agg)), solution conductance and microfluidity, and average aggregate size and polydispersity, are observed to change as either [hmim][Br] or HeTAB is added to aqueous CTAB; the experimental outcomes clearly imply the changes in most of the physicochemical properties to be significantly more dramatic in case of IL [hmim][Br] addition. The fact that, between the two, only IL [hmim][Br] may show cosolvent-type behavior at high concentrations is evoked to explain the differences in the behavior of the two additives. It is demonstrated that both [hmim][Br] and HeTAB show electrolytic as well as cosurfactant-type behavior within aqueous CTAB when present at low concentrations, with the changes in physicochemical properties being very similar. At high concentrations, although HeTAB still acts as a cosurfactant forming mixed micelles with CTAB, IL [hmim][Br] behaves partly as a cosolvent toward altering the physicochemical properties of aqueous CTAB. The unique role of IL in changing properties of aqueous surfactant systems is demonstrated.

Interaction between ionic liquid and zwitterionic surfactant: A comparative study of two ionic liquids with different anions

Room temperature ionic liquids (ILs) may have enormous potential as far as modifying the properties of aqueous surfactant solutions is concerned. A comparative study on the changes in the physicochemical properties of aqueous solution of a commonly used zwitterionic surfactant N-dodecyl- N , N -dimethyl-3-ammonio-1-propanesulfonate (SB-12) in the presence of up to 2 wt% of two ILs with same cation but different anions is undertaken using conductance, fluorescence spectroscopy, and dynamic light scattering. The two ILs used are 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6]). It is demonstrated that the addition of IL alters the important properties of aqueous SB-12. Critical micelle concentration, aggregation number, micellar size, and microfluidity of micellar pseudo-phase change when the IL is added to aqueous SB-12. The extent to which these properties are altered is observed to be significantly more for [bmim][PF 6] as compared to that for [bmim][BF 4]. The results demonstrate the presence of electrostatic attractive interactions between the ions of ILs and the zwitterion of SB-12 to be the major reason for these observations. While the interaction between the IL cation and the anionic sulfonate termini of SB-12 is same for the two ILs, that between IL anion and cationic quaternary ammonium of SB-12 is proposed to be more efficient for [bmim][PF 6] due to the bigger size of PF 6 − . Important role of IL anion in modifying properties of aqueous SB-12 is demonstrated. It is noted that the changes in the properties of aqueous surfactant systems upon IL addition depend strongly on the nature of the surfactant head group.

Zeta Potentials and Debye Screening Lengths of Aqueous, Viscoelastic Surfactant Solutions (Cetyltrimethylammonium Bromide/Sodium Salicylate System)

In a series of experiments, we studied the dynamic properties of aqueous surfactant solutions of cetyltrimethylammonium bromide (CTAB) at conditions after adding different amounts of sodium salicylate (NaSal). The aggregates, present in these solutions, are elongated, wormlike micelles, which tend to form entanglement networks. The viscoelastic, gel-like samples were analyzed by means of static, dynamic, and electrophoretic light scattering techniques. We separately investigated the effects of surfactant concentration and added salt on intermicellar interactions. The electrostatic interactions between the anisometric micelles were analyzed by considering the effective dimensions of the aggregates. We calculated the Debye-Huckel lengths from experimental data of the osmotic second virial coefficient and from the diffusion second virial coefficient. It turned out that the results were in good agreement with theoretically estimated values. We also measured the zeta potential and intensity of scattered light in a large range of different salt concentrations keeping the CTAB concentration constant. We observed an isoelectric point and charge reversal of the threadlike micelles at an excess salicylate concentration of about 100 mM. The observed decrease of the zeta potential points to striking processes of counterion condensation. In these solutions, the salicylate ion acts as a cosurfactant, due to its discrepancy between polar and hydrophobic groups. We also detected a simple linear correlation between the zeta potentials and the Debye screening lengths of the surfactant solutions.

Ionic Liquid Induced Changes in the Properties of Aqueous Zwitterionic Surfactant Solution

Modifying properties of aqueous surfactant solutions by addition of external additives is an important area of research. Unusual properties of ionic liquids (ILs) make them ideal candidates for this purpose. Changes in important physicochemical properties of aqueous zwitterionic N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) surfactant solution upon addition of hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4], are reported. Dynamic light scattering results indicate a dramatic reduction in the average micellar size in the presence of [bmim][BF 4]; micellar (or micelle-like) aggregation in the presence of as high as 30 wt % [bmim][BF 4] is confirmed. Responses from fluorescence probes are used to obtain critical micelle concentration (cmc), aggregation number ( N agg), and dipolarity and microfluidity of the micellar pseudophase of aqueous SB-12 in the presence of [bmim][BF 4]. In general, increasing the amount of [bmim][BF 4] to 30 wt % results in decrease in N agg and increase in cmc. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the micellar pseudophase is observed on increasing [bmim][BF 4] concentration in the solution. It is attributed to increased water penetration into the micellar pseudophase as [bmim][BF 4] is added to aqueous SB-12. It is proposed that IL [bmim][BF 4] behaves similar to an electrolyte and/or a cosurfactant when present at low concentrations and as a polar cosolvent when present at high concentrations. Electrostatic attraction between cation of IL and anion of zwitterion, and anion of IL and cation of zwitterion at low concentrations of [bmim][BF 4] is evoked to explain the observed changes. Presence of IL as cosolvent appears to reduce the efficiency of micellization process by reducing the hydrophobic effect.

Unique role of hydrophilic ionic liquid in modifying properties of aqueous Triton X-100

Modification of important physicochemical properties of aqueous surfactant solutions can be achieved by addition of environmentally benign room temperature ionic liquids (ILs). While low aqueous solubility of "hydrophobic" ILs limits the amount of IL that may be added to achieve desired changes in the physicochemical properties, hydrophilic ILs do not have such restrictions associated to them. Alterations in the key physicochemical properties of aqueous solutions of a common nonionic surfactant Triton X-100 (TX100) on addition of up to 30 wt % hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) are reported. The presence of micellar aggregates in as high as 30 wt % [bmim][BF4]-added aqueous TX100 solutions is established by dynamic light scattering and fluorescence probe behavior. Increasing the concentration of [bmim][BF4] results in decrease in average micellar size and aggregation number and increase in critical micelle concentration, indicating an overall unfavorable aggregation process. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the palisade layer of the micellar phase upon [bmim][BF4] addition implies increased water penetration and the possibility of TX100-[bmim][BF4] interactions. While the changes in some of the physicochemical properties indicate the role of [bmim][BF4] to be similar to a cosurfactant, the IL acts like a cosolvent as far as changes in other properties are concerned. Effectiveness of IL [bmim][BF4] in modifying physicochemical properties of aqueous TX100 is demonstrated.

Concentration-Dependent Dual Behavior of Hydrophilic Ionic Liquid in Changing Properties of Aqueous Sodium Dodecyl Sulfate

Modifying physicochemical properties of aqueous surfactant solutions in favorable fashion by addition of environmentally benign room-temperature ionic liquids (ILs) has enormous future potential. Due to its unusual properties, an IL may demonstrate a unique role in altering the properties of aqueous surfactant solutions. Changes in the properties of aqueous sodium dodecyl sulfate (SDS), an anionic surfactant, upon addition of a common and popular "hydrophilic" ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] are presented. Addition of low concentrations of [bmim][BF4] (i.e., <or=2 wt %) to aqueous SDS results in a decrease in critical micelle concentration (cmc) as well as an increase in aggregation number (N(agg)) and average micellar size. An increase in dipolarity and a decrease in microfluidity of the micellar phase is reported by solvatochromic fluorescence probes pyrene and 1,3-bis-(1-pyrenyl)propane as up to 2 wt % [bmim][BF4] is added to aqueous SDS. The IL is observed to behave similarly to common electrolytes in the concentration range 0 < [bmim][BF4] <or= 2 wt %. A further increase in [bmim][BF4] concentration to 30 wt % results in an increase in cmc which is accompanied by a decrease in N(agg) and average micellar size. Change in the microfluidity of the micellar phase is observed to become insignificant in this concentration range. Evidence of the presence of micellar aggregates at such high concentration of [bmim][BF4] is furnished by dynamic light scattering. The role of an IL in altering the properties of aqueous SDS in the range 2 wt % < [bmim][BF4] <or=30 wt % is similar to those of polar cosolvents. The concentration-dependent dual role of the IL [bmim][BF4] in altering physicochemical properties of aqueous SDS is demonstrated.

Modulating properties of aqueous sodium dodecyl sulfate by adding hydrophobic ionic liquid

Altering and modifying important physicochemical properties of aqueous surfactant solutions is highly desirable as far as potential applications of such systems are concerned. Changes in the properties of aqueous solutions of a common anionic surfactant sodium dodecyl sulfate (SDS) are assessed in the presence of a common and popular ‘hydrophobic’ ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF 6). Upon addition of up to ∼ 0.10 wt % bmimPF 6, a dramatic decrease in critical micelle concentration (cmc) is accompanied by an increase in the degree of counterion dissociation ( α) and micellar aggregation number ( N agg ) indicating micellar growth. However, in the range 0.10 wt% ⩽ bmimPF 6 ⩽ 2.00 wt%, relatively gradual decrease in α and N agg is observed along with no change in cmc. Significantly decreased microfluidity of the aqueous SDS solutions on addition of bmimPF 6 is indicated by a fluorescence microviscosity probe 1,3- bis-(1-pyrenyl)propane which suggests partitioning of bmimPF 6 into the SDS micellar phase. Behavior of solvatochromic fluorescence probes, pyrene, pyrene-1-carboxaldehyde, and 2-( p-toluidino)naphthalene-6-sulfonate, confirms interaction, and possible complexation, between IL bmimPF 6 and anionic micellar surface. Increased solubility of bmimPF 6 with increasing SDS concentration further confirms SDS-bmimPF 6 interactions. Presence of strong electrostatic attraction between bmim + and anionic micellar surface is proposed to be the most dominant reason for these observations. All-in-all, unique role of a hydrophobic ionic liquid bmimPF 6 in modifying the properties of aqueous anionic sodium dodecyl sulfate is demonstrated.

Effect of added fragrances on the foaming properties of aqueous surfactant solutions

Foaming properties are important characteristics of surfactant solutions used for personal washing products, hair styling foam, shaving foam, etc. Fragrances are often used in these cosmetic products, but they also influence the foaming properties of aqueous surfactant solutions. In this study, we investigated the effects of added fragrances [d‐limonene (LN), α‐hexyl‐cinnamic‐aldehyde (HCA), β‐ionone (IN), benzyl acetate (BA), linalool (LL), geraniol (GL), eugenol (EL), and cis‐3‐hexenol (HL)] on the initial foam heights and foam stability of sodium dodecyl sulphate (SDS) aqueous solutions. GL and EL increase the initial foam heights of 0.1 wt% and 0.3 wt% SDS aqueous solutions. Dynamic surface tension measurement shows that these fragrances quickly lower the surface tension of SDS solutions. Hence, GL and EL increase the initial foam heights because of the fast adsorption at the air/water interface. Further, GL and EL also increase the foam stability of SDS solutions and act as foam boosters. For the application to shampoo, the addition of GL results in the largest improvement of the initial foam height and the foam stability among the fragrances investigated here.

Effect of Novel Alkanolamides on the Phase Behavior and Surface Properties of Aqueous Surfactant Solutions

The surface tension properties and phase behavior of a new series of alkanolamides, alkanoyl N‐methyl ethanolamides (NMEAs) and their mixtures with sodium dodecyl sulfate (SDS) were investigated. NMEAs alone do not form micelles in aqueous solutions but reduce considerably the surface tension until macroscopic phase separation occurs. According to Gibbs isotherms, the surface layer is less compact for the NMEA with the shortest alkanoyl chain. The critical micelle concentration (CMC) of SDS solutions is greatly reduced upon addition of a small amount of NMEA and the magnitude of this effect increases with the length of the alkanoyl group. The results indicate the presence of attractive interactions between SDS and NMEA molecules inside micelles. The mixing of SDS with NMEA‐16 causes a reduction in the melting temperature of the solid similar to freezing‐point depression in a binary system. On the other hand, the eutectic temperature is higher in SDS‐conventional dodecanoyl mono ethanolamide (DMA) systems in which the mixture is in a solid state at room temperature over a wide range of mixing fractions. Among NMEAs, surface tension decay is faster as the alkanoyl chain length decreases. Only for the dodecanoyl chain could a diffusion‐controlled adsorption be identified at low concentrations. When small amounts of NMEA are added to SDS aqueous solutions, the surface tension decay is retarded; however, and at long times a lower surface tension is reached. For NMEA/SDS and DMA/SDS systems, an adsorption barrier is likely present. The magnitude of this barrier seems to depend on the SDS/alkanolamide ratio.

Kinetics of Cosurfactant−Surfactant−Silicate Phase Behavior. 1. Short-Chain Alcohols

The formation of hexagonal and lamellar surfactant−silicate mesophases at room temperature has been investigated by in situ synchrotron small angle X-ray scattering. Emphasis was given to the influence of butanol and hexanol on the surfactant−silicate phase behavior. The experimental setup included a continuous flow reactor allowing a resolution in time as high as 0.3 s. Depending on the reaction composition, one, two, or three coexisting phases were observed. The results are discussed in terms of time-dependent changes in the concentration of cosurfactant not incorporated into the composite aggregates. Although many of the observed effects are paralleled by well-known properties of aqueous surfactant solutions, important dissimilarities exist. Furthermore, the relative intensity of the high-order reflections are suggested to correspond to the degree of interaggregate condensation in the composite mesophase.