Phase behavior of diglycerol fatty acid esters (Qn-D, where n represents the carbon number in the alkyl chain length of amphiphile, n = 10-16) were investigated in different nonpolar oils, liquid paraffin (LP70), squalane, and squalene. There is surfactant solid at lower temperature, and the surfactant solid does not swell in oil, and the melting temperature is almost constant in a wide range of compositions. In all of the systems, a lamellar liquid crystal (L(alpha)) is formed in a concentrated region at a temperature between the solid melting temperature and the isotropic two- or single-phase regions. In the dilute regions, reverse vesicles are formed in L(alpha) + O regions. There are two liquid-phase regions above the L(alpha) present region. This two-phase boundary corresponds to the cloud-point curve of nonionic surfactant aqueous solutions. However, instead of being less soluble in water at high temperature for the cloud point, the surfactant becomes more soluble in the organic solvents at high temperature. Namely, the effect of temperature on the solubility is opposite to the clouding phenomenon. When the hydrocarbon chain of the diglycerol surfactant decreases, the two-phase region becomes wider. In the case of a fixed surfactant, the surfactant is most miscible with squalene (narrowest two-phase regions) and the order of dissolutions tendency is squalene > LP70 > squalane. These results show that the hydrophilic moiety (diglycerol group) is more insoluble in oil compared with that of a conventional poly(oxyethylene)-type nonionic surfactant. Formation of reversed rodlike micelles was confirmed by SAXS scattering curve. When the hydrocarbon chain of surfactant is short, the micellar size becomes larger. In a fixed surfactant system, the reverse micellar size increases by changing oil from squalene to LP70. A small amount of water induces a dramatic elongation of reverse micelles.

Upon the addition of a short EO chain nonionic surfactant, poly(oxyethylene) dodecyl ether (C12EOn), to dilute micellar solution of sodium dodecyl sulfate (SDS) above a particular concentration, a sharp increase in viscosity occurs and a highly viscoelastic micellar solution is formed. The oscillatory-shear rheological behavior of the viscoselastic solutions can be described by the Maxwell model at low shear frequency and combined Maxwell-Rouse model at high shear frequency. This property is typical of wormlike micelles entangled to form a transient network. It is found that when C12EO4 in the mixed system is replaced by C12EO3 the micellar growth occurs more effectively. However, with the further decrease in EO chain length, phase separation occurs before a viscoelastic solution is formed. As a result, the maximum zero-shear viscosity is observed at an appropriate mixing fraction of surfactant in the SDS-C12EO3 system. We also investigated the micellar growth in the mixed surfactant systems by means of small-angle X-ray scattering (SAXS). It was found from the SAXS data that the one-dimensional growth of micelles was obtained in all the SDS-C12EOn (n=0-4) aqueous solutions. In a short EO chain C12EOn system, the micelles grow faster at a low mixing fraction of nonionic surfactant.

The aqueous phase behavior and preparation of mesoporous silica by new fluorinated surfactants C8F17SO2(C3H7)N(C2H4O)nH (abbreviated C8F17(EO)n) is reported here. C8F17(EO)n forms elongated micelles and liquid crystals in water. Mesostructured silica was prepared by the cooperative self-assembly precipitation method and a systematic study was carried out, investigating the influence of surfactant and silica precursor (TEOS) concentrations, pH and the effect of poly(ethylene oxide) chain lengths. The resulting materials were characterized by SAXS, nitrogen sorption and TEM. The pore inner diameters are small (⩽35Å) and the pore walls are thick (>20Å). The materials possess high specific surface areas (≈1000m2/g), which are achieved at very small surfactant concentrations (2wt.%), producing robust thick walls with no significant microporosity. The specific surface area is preserved during calcination despite a small shrinkage attributed to silica cross-linking. The d-spacing appeared invariable over a wide range of surfactant/SiO2 ratios, between 0.006 and 1 molar ratios. Hexagonal ordered (p6mm) mesopores were formed at HCl concentrations higher than 0.1M, while disordered worm-like mesopores were obtained at HCl concentrations lower than 0.1M. The optimum ethylene oxide chain length to obtain well-ordered mesoporous hexagonal silica corresponded to 10 ethylene oxide units.

The phase behavior in water of pentaglycerol monostearate (C(18)G(5)) and pentaglycerol monooleate (C-18:1 G(5)) surfactants has been studied as a function of temperature and surfactant weight fraction, W-s . The equilibrium phases present at each composition and temperature studied were characterized by means of visual observation under normal and polarized light, differential scanning calorimetry (DSC), and X-ray scattering, both at small (SAXS) and at wide angle (WAXS). In the temperature range 0-46 degrees C, C(18)G(5) presents a thermotropic alpha-gel structure. However, at higher temperatures, the alpha-gel phase melts and a lamellar liquid crystalline (L-alpha) phase is formed. The amount of water that can be solubilized by alpha-gel and L-alpha was determined by plotting the interlayer distance, d , as a function of the reciprocal of W-s . Water is soluble in the alpha-gel phase up to 21 w/w% water concentration and in the L-alpha phase up to 30 w/w% water concentration. At higher water concentrations, excess water appears and a dispersion of alpha-gel (alpha-gel+W) and lamellar liquid crystal (L-alpha +W) in water is formed, respectively. In contrast, C-18:1 G(5) is liquid in the whole range of temperatures studied (0-100 degrees C). While at low temperatures, C-18:1 G(5) presents a L-alpha structure, at about 63 degrees C L-alpha melts and an isotropic liquid reverse micellar solution (O-m ) phase is formed. The amount of water that can be solubilized by both O-m and L-alpha increases with temperature.

The equilibrium and dynamic surface tension properties in aqueous solutions of nonionic and cationic fluorinated surfactants bearing a sulfonated group are reported. Both surfactants show low critical micellar concentration and very low equilibrium surface tension values, but the cationic surfactant is more effective at decreasing surface tension, which is attributed to a small surface area per molecule. In dynamic surface tension measurements both surfactants show an induction time, which is longer for the nonionic surfactant with a higher molecular weight, slower diffusion rates, and higher molecular surface area. The dynamic behavior of surface tension is modeled by a series of exponentials from which a relaxation time for surface tension decay can be estimated. This relaxation time is faster for the cationic surfactant and decreases with both surfactant concentration and temperature. In mixtures of both surfactants, the values of the relaxation time are between those of the pure surfactants, indicating neither synergism nor antagonism.

A study of the phase and rheological behavior of sucrose hexadecanoate (C16SE)/cosurfactant/water systems in the presence of solubilized oil, using complementary techniques such as dynamic light scattering and small angle X-ray scattering, is presented. Viscoelastic wormlike micellar solutions are found when a nonionic lipophilic cosurfactant is added to C16SE aqueous systems. Contrary to previous reports, the effect of oil solubilization on these wormlike micelles is not unique and depends on several factors. Linear alkyl chain oils that tend to solubilize in the micellar core have a disrupting effect, decreasing the relaxation time and the viscosity of the systems. This effect is larger as the molecular volume of oil increases and as the solubility of the cosurfactant in oil increases. On the other hand, oils that penetrate in the palisade layer, such as p-xylene, induce micellar growth and have a thickening effect at a given micellar composition. Thermodynamic considerations are used to explain the experimental results.

The phase behavior of the water/poly(oxyethylene)-poly(dimethylsiloxane) copolymer (Si25C3EO51.6)/pentaoxyethylene dodecyl ether (C12EO5) ternary system has been studied. Both the silicone copolymer and the surfactant have equal volumes of hydrophilic and lipophilic parts; i.e., these are balanced amphiphiles. Although only a lamellar phase is observed in water-Si25C3EO51.6 and water-C12EO5 binary systems, a variety of liquid crystalline phases, including normal micellar cubic (I1), hexagonal (H1), bicontinuous cubic (V1), lamellar (L(alpha)), reverse bicontinuous cubic (V2), and reverse hexagonal (H2), are observed in the copolymer-rich region of the ternary phase diagram. The small C12EO5 molecules dissolve at the hydrophobic interface in the thick bilayer of the Si25C3EO51.6 L(alpha) phase occupying a large area of the total interface of the aggregates and modulate the curvature of the aggregates. Hence a variety of self-assembled structures are observed. In contrast, Si25C3EO51.6 is not dissolved in the thin bilayer of the C12EO5 lamellar phase (L'(alpha)). Hence, the C12EO5 L'(alpha) phase coexists with copolymer-rich L(alpha) and H2 phases. Consequently, small surfactant molecules are dissolved in a large silicone copolymer aggregate to induce a change in layer curvature, but a large copolymer molecule is hard to incorporate with surfactant aggregates.

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.

Static and dynamic surface tension and interfacial rheological behavior of a novel anionic gemini-type surfactant without a spacer group, sodium 2,3-didodecyl-1,2,3,4-butane tetracarboxylate (GS), were investigated. Very low values for critical micelle concentration (8.9 x 10(-5) M) as well as equilibrium surface tension (22.7 mN m(-1)) were observed for the aqueous solutions. Dynamic surface tension (DST) is very slow and less sensitive to the surfactant concentration than the conventional monomeric surfactant, suggesting the presence of a significant adsorption barrier for GS owing to a complicated molecular structure. Presence of a small concentration of GS in sodium dodecyl sulfate (SDS) solution shows a synergistic effect to form mixed micelles and lowers the cmc considerably. This synergism between GS and SDS and slow exchange of GS between bulk and interface create a rigid air-liquid interface of the SDS-GS solution, which is reflected in a higher elasticity value for the interface of the SDS-GS solution than for the SDS solution. It has been found that the presence of a small concentration of GS in SDS solution increases the foam stability noticeably. Although the stability of the wet foam is correlated with the film elasticity, the stability of dry foam cannot be explained in terms of film elasticity alone. (c) 2005 Elsevier Inc. All rights reserved.

A comparative study on rheology and microstructure of direct and reverse liquid-crystal phases in a single-block copolymer/oil/water system using rheometry and small-angle X-ray scattering (SAXS) is presented. The microstructure of reverse phases is less sensitive to an increase in temperature, since changes in surface curvature are limited, whereas in the case of direct phase, a decrease in the effective surface area promotes structural transitions. The studied hexagonal and micellar cubic phases show gel-like behavior under the experimental conditions used, but the values of the plateau elastic modulus are one order the magnitude higher for micellar cubic phases. Rheological parameters show values of the same order of magnitude for reverse and direct phases of same morphology, although direct phases show slightly higher elastic modulus and complex viscosity, probably reflecting the effect of the continuous phase. In some cases, a correlation between rheology and microstructural changes was found.

The phase behavior and microstructure of mixed nonionic surfactant systems containing poly(oxyethylene) cholesteryl ether (ChEOn, n=15 and 10), a new alkanolamide-type foam booster, dodecanoyl N -methylethanolamide (NMEA-12), and water, were investigated at 25 degrees C by means of visual observation and small-angle X-ray scattering. In the ChEO(15)/water binary system, aqueous micellar (W(m)), discontinuous cubic liquid crystal (I(1)), hexagonal (H(1)), rectangular ribbon (R(1)), lamellar (L(alpha)), and solid (S) phases are successively formed with increasing surfactant concentration. Although the R(1) phase is an intermediate phase formed in a very narrow composition range in conventional surfactant systems, its domain is unusually wider than that of H(1), which may be attributed to the packing constraint caused by the bulky cholesteric group in the lipophilic core of the aggregate. Upon addition of lipophilic NMEA-12 to the ChEO(15)/water binary system, the interfacial curvature of the aggregates decreases, and the micellar or liquid crystal phases formed in the binary system transform to the reverse micellar (O(m)) phase via the L(alpha) phase existing over a wide concentration range. The SAXS results establish an epitaxial relationship between the (11) plane of the R(1) phase and the (10) plane of the L(alpha) phase. The ChEO(10)/NMEA-12/water system shows a phase diagram of similar general appearance, except that the W(m) to R(1) phase transformation occurs via an optically anisotropic liquid crystal phase of unknown structure and the R(1) to L(alpha) phase transition occurs through a narrow intermediate defected lamellar (L(alpha)(H)) phase. The variation in the aggregate size and shape and the unit cell of the R(1) phase formed in ChEOn/NMEA-12/water systems is also discussed.

Si14C3EO n and Si25C3EO n form reverse micellar solution (O m ), reverse discontinuous cubic, (I2), reverse hexagonal (H2) and lamellar (Lα) phases in water with increasing EO chain lengths, n, or its volume ratio to the surfactant, f were investigated. However, the H2 and I2 phases are stabilized in a wide range of f in water+Si25C3EO n than that in water+Si14C3EO n . Similar phase sequence, O m -I2-H2-Lα was observed in Si m C3EO n /D4 systems with the increase of the volume in the hydrophilic moiety. In water binary systems, all the homogeneous phases are in equilibrium with excess water, whereas the liquid crystalline phases are systematically changed to the O m phase via inter-existing phases in D4 systems because the surfactant layer curvature changes towards more negative due to the increase of effective lipophilic volume by added D4.

The phase behavior of a mixture of poly(isoprene)-poly(oxyethylene) diblock copolymer (PI-PEO or C250EO70) and poly(oxyethylene) surfactant (C12EO3, C12EO5, C12EO6, C12EO7, and C12EO9) in water was investigated by phase study, small-angle X-ray scattering, and dynamic light scattering (DLS). The copolymer is not soluble in surfactant micellar cubic (I1), hexagonal (H1), and lamellar (Lalpha) liquid crystals, whereas an isotropic copolymer fluid phase coexists with these liquid crystals. Although the PI-PEO is relatively lipophilic, it increases the cloud temperatures of C12EO3-9 aqueous solutions at a relatively high PI-PEO content in the mixture. Most probably, in the copolymer-rich region, PI-PEO and C12EOn form a spherical composite micelle in which surfactant molecules are located at the interface and the PI chains form an oil pool inside. In the C12EO5/ and C12EO6/PI-PEO systems, one kind of micelles is produced in the wide range of mixing fraction, although macroscopic phase separation was observed within a few days after the sample preparation. On the other hand, small surfactant micelles coexist with copolymer giant micelles in C12EO7/ and C12EO9/PI-PEO aqueous solutions in the surfactant-rich region. The micellar shape and size are calculated using simple geometrical relations and compared with DLS data. Consequently, a large PI-PEO molecule is not soluble in surfactant bilayers (Lalpha phase), infinitely long rod micelles (H1 phase), and spherical micelles (I1 phase or hydrophilic spherical micelles) as a result of the packing constraint of the large PI chain. However, the copolymer is soluble in surfactant rod micelles (C12EO5 and C12EO6) because a rod-sphere transition of the surfactant micelles takes place and the long PI chains are incorporated inside the large spherical micelles.

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.

The rheological behavior of micellar cubic phases in C12EO25 systems and related emulsions has been investigated. In the aqueous C12EO25 binary system, the transition from the cubic phase to the micellar solution is associated with a sudden drop in viscosity and with a small enthalpy of transition. The elastic modulus and viscosity of the cubic phases show a maximum with concentration but remain very high within the range of existence of the cubic phase. Several relaxation processes seem to be present in binary cubic phases, and some of them occur in a time scale that can be followed by both rheology and dynamic light scattering measurements. Upon addition of a small amount of oil (decane), the rheological behavior changes remarkably. As the oil fraction increases, the relaxation times also increase and, finally, highly concentrated, gel-like emulsions are obtained. Contrary to conventional concentrated emulsions, the viscosity of cubic-phase-based emulsions is decreased by increasing the fraction of the dispersed phase. The non-Maxwellian rheological behavior at low oil fractions is described according to the model of slipping crystalline planes, modified by using a distribution of bulk relaxation times, and good fitting to the experimental data is obtained.

Different from conventional nonionic poly(oxyethylene) surfactants, poly(oxyethylene) cholesteryl ethers, ChEO(n), possess a bulky and nonflexible hydrophobic part and form a variety of self-organized structures in water. We investigated the phase behavior and the micellar structures in the water/ChEO(15) and water/ChEO(10) systems by means of visual observation, rheometry, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), dielectric relaxation spectroscopy (DRS), and densimetry. We found that in the water/ ChEO(15) system, aqueous micellar (W-m), discontinuous micellar cubic (I-1) with Fd3m space group, hexagonal (H-1), rectangular ribbon (R-1), and lamellar (L-alpha) phases are formed, whereas W-m, unknown, R-1, defected lamellar (L-alpha(H)), and L-alpha phases are produced in the water/ChEO(10) system at ambient temperatures. Compared with a conventional aqueous nonionic surfactant system, the intermediate R-1 phase region is incredibly wide. As for the water/ChEO(15) system, with increasing water content, the packing parameter, P, in the R-1 region is gradually decreased, finally converging to 1/2 at W-s similar to 0.58, indicative of the formation of the H-1 phase. The R-1 phase acts as a "distorted" hexagonal phase in the system. However, in the water/ChEO(10) system, upon reduction of W-S, P shows a steplike increase and the maximum value similar to0.67 at W-S similar to 0.7, just corresponding to the threshold of discontinuous and bicontinuous structures. After that, P is decreased with decreasing Ws and unknown phase that cannot be indexed to any known space group for liquid crystalline phases emerges at W-S similar to 0.5. The GIFT analysis of the SAXS data for the W-m solution indicates that spherical micelles are present in the water/ChEO15 system in an ambient temperature range, but ChEO(10) forms a short-rod micelle in water. With increasing temperature, rodlike micelles appear to be grown and a viscoelastic micellar phase is formed in water/ChEO10 system. The hydration number for each oxyethylene unit is evaluated as similar to4 by DRS, which gives a consistent explanation for the concentration dependence of the apparent hydrodynamic radius in the Wm phase obtained by DLS. Hydrated water molecules should be regarded as a constituent of the micelles. The majority of these features of novel phase behavior in the water/ChEO(n) systems are based on a nonflexible and bulky hydrophobic part of ChEO(n).

A novel anionic gemini-type surfactant with no spacer group, disodium 2,3-didodecyl-1,2,3,4-butanetetracarboxylate (GS)-was investigated for its phase behavior in water, water/decane, and water/cosurfactant systems in a wide range of compositions. At low surfactant concentration in the GS-water binary system, a micellar solution phase is formed which transforms to a hexagonal (H-1) phase, as in conventional ionic surfactant systems. At high GS concentration, however, the H-1, phase transforms to the rectangular-ribbon (R-1) liquidcrystal phase. Since the GS molecule has no spacer group, a small cross-sectional area of the headgroup and closely packed hydrophobic chain tend to increase the packing constraints of the lipophilic core with increasing surfactant concentration, thereby inducing the H-1-R-1 phase transition. In the presence of a normal hydrocarbon like decane, the H-1, phase is changed to a micellar cubic phase. On the other hand, the surfactant layer curvature becomes less positive upon addition of a lipophilic amphiphile because it is solubilized in the palisade layer of the aggregate. Addition of short poly(oxyethylene) chain nonionic surfactant (CmEOn, where m, n = 12, 3; 12, 4; and 16, 4) to the aqueous GS solution in a dilute region increases the viscosity by several orders and forms a transparent and viscoelastic micellar solution showing the rheological properties of typical wormlike micelles, with Maxwellian behavior in low oscillatory frequency. In the GS-C12EO3 and also in the GS-C16EO4 systems, the viscosity values are significantly higher than the reported values for dimeric surfactants of similar chain length.

We report on the phase behavior and structural evolution during the early stages of silica templating using surfactant liquid crystals in aminoalkoxysilane/lauric acid/water systems. Specific aminoalkoxysilanes are used so that hydrolysis and condensation reactions are slow enough to follow the changes in the early stages of mesoporous silica formation without the need for very sophisticated techniques. A lyotropic lamellar phase that swells with water is present in the early stages of the system and develops into kinetically correlated siliceous phases with preservation of morphology. Moreover, lyotropic and siliceous phases coexist at a certain time. Hydrolysis and condensation of alkoxysilane groups cause microstructural changes in the lyotropic lamellar phase, as monitored by in situ small-angle X-ray scattering and infrared spectroscopy measurements. Although the changes in the initial lamellar phase depend on the nature of the alkoxysilane groups, the final siliceous phases show similar correlation lengths, which are close to that of previously reported lamellar mesoporous materials. The results indicate three stages during liquid crystal templating, controlled respectively by self-assembly, hydrolysis, and condensation of alkoxysilane groups on the surface of aggregates. A mechanism, based on phase separation, is proposed for the formation of these hybrid organic-inorganic materials.