Microemulsion formed by alkyl polyglucoside and an alkyl glycerol ether with weakly charged films

We have studied the effects on phase equilibria of a nonionic surfactant mixture-water-oil system when replacing small amount of surfactant molecules by ionic surfactant, sodium dodecyl sulfate (SDS). The nonionic surfactant system contains dodecyl-beta-D-maltoside (C(12)AG2) and iso-octyl glyceryl ether (i-C(8)GE) as cosurfactant, water and cyclohexane at constant water to oil ratio of 60/40 (w/w). Adding a small amount of SDS has large impact on the phase behavior. Clear liquid crystalline phase and upper microemulsion phase are added to the phase sequence at high i-C(8)GE/(C(12)AG2+i-C(8)GE) ratio. We also compare the phase equilibria of pure dodecyl maltoside system with polyglucosides mixture system.     

Quantitative effect of nonionic surfactant partitioning on the hydrophile-lipophile balance temperature

Phase behaviors of water/nonionic surfactants/isooctane systems are determined experimentally in temperature-global surfactant concentration diagrams. The surfactants are monodistributed polyoxyethylene glycol n-dodecyl ether. They are used as model mixtures of two, three, or five compounds or as constituents of a commercial surfactant. It is found that the phase diagrams of these systems are bent gradually toward the highest temperatures as the global surfactant concentration decreases. Each phase diagram is well-characterized by the curve of the HLB (hydrophile-lipophile balance) temperature versus the global surfactant concentration. For any fixed global surfactant concentration, this temperature is the middle temperature of the three-phase region; it can be calculated from an additive rule of the HLB temperatures of the surfactants weighted by their mole fractions at the water/oil interface. These mole fractions are determined through the pseudophase model using surfactant partitioning. Calculations require the knowledge of the critical micelle concentration, the partition coefficient between water and oil, and the HLB temperature of each surfactant of the mixture. This treatment can be used to correctly predict the variation of the HLB temperatures of the surfactant mixtures studied versus the global surfactant concentration. Furthermore, these calculations show that the observed curvature of the phase diagrams at the lowest global concentrations is due to the most favorable partitioning toward the oil of the lowest ethoxylated surfactant molecules.     

混合表面活性剂微乳状液的形成和相行为研究进展

讨论了单一表面活性剂,混合表面活性剂,助溶剂等对油／水微乳状液的形成和相行为的影响。对混合表面活性剂微乳状液的形成和相行为研究工作进行了归纳和总结,重点分析了正负离子表面活性剂微乳状液的相行为和表面活性剂微乳状液的相行为和表面活性剂效率,讨论了微乳状液形成的影响因素,并提出了这一研究领域可能的发展前景。     

Phase Behavior, Structure, and Physical Properties of the Quaternary System Tetradecyldimethylamine Oxide, HCl, 1-Hexanol, and Water

The phase diagram of the ternary surfactant system tetradecyldimethylamine oxide (TDMAO)/HCl/1-hexanol/water shows with increasing cosurfactant concentration an L(1) phase, two L(alpha) phases (a vesicle phase L(alpha1) and a stacked bilayer phase L(alphah)), and an L(3) phase, which are separated by the corresponding two-phase regions L(1)/L(alpha) and L(alpha)/L(3). In this investigation, the system was studied where some of the TDMAO was substituted by the protonated TDMAO. Under these conditions, one finds for constant surfactant concentration of 100 mM TDMAO a micellar L(1) phase, an L(alpha1) phase (consisting of multilamellar vesicles), and an interesting isotropic L(1)(*) phase in the middle of the L(1)/L(alpha) two-phase region. The L(1)(*) phase exists at intermediate degrees of charging of 30-60% and for 40-120 mM TDMAO and 70-140 mM hexanol concentration. At surfactant concentrations less than 80 mM the L(1)(*)-phase borders directly on the L(1) phase. The phase transition between the L(1) phase and the L(1)(*) phase was detected by electric conductivity and rheological measurements. The conductivity values show a sharp drop at the L(1)/L(1)(*) transition, and the zero shear viscosity of the L(1)(*) phase is much lower than in L(1) phase. The form and size of the aggregates in L(1)(*) were detected with FF-TEM and SANS. This phase contains small unilamellar vesicles (SUV) of about 10 nm and some large multilamellar vesicles with diameters up to 500 nm. The system exhibits another peculiarity. For 100 mM surfactant, the clear L(alpha1)-phase exists only at chargings below 30%. With oscillating rheological measurements a parallel development of the storage modulus G' and the loss modulus G" was observed. Both moduli are frequency independent and the system possesses a yield stress. The storage modulus is a magnitude larger than the loss modulus. Copyright 2000 Academic Press.     

Microemulsification of triglyceride sebum and the role of interfacial structure on bicontinuous phase behavior

A unique triblock surfactant is reported that allows for the efficient microemulsification of triglycerides. Unlike the results of all previous efforts, these triglyceride microemulsions can be formed without the use of cosurfactants or dilution with co-oils and follow the classical patterns of surfactant phase behavior exhibited by mixtures of water, alkane oils, and nonionic oligoethylene glycol surfactants, i.e., progression from oil/water emulsions to one-phase microemulsions to water/oil emulsions with increasing temperature. Lamellar phases that usually dominate the aqueous phase behavior of surfactant/triglyceride mixtures are suppressed, allowing for the formation of single-phase microemulsions containing equal amounts of triglyceride and water. These isotropic and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. The effects of mixing a variety of typical skin care ingredients and components of sebum (skin oil) were also explored. Fatty acids significantly reduce the average microemulsion temperature, while other ingredients and oils, which do not partition at the oil/water interface, have less impact on the phase behavior. In all cases, one-phase microemulsions containing equal amounts of oil and water can be formed even at high additive concentrations. Indeed, partial replacement oftriglyceride with any of the additives examined consistently reduced the amount of surfactant necessary to form single-phase microemulsions. However, the greatest boost in surfactant efficiency was found with the addition of medium molecular weight amphiphilic block copolymers.     

Phase behavior of salt-free catanionic surfactant aqueous solutions with fullerene C60 solubilized

A salt-free catanionic surfactant system, tetradecyltrimethylammonium laurate (TTAL), was constructed by mixing tetradecyltrimethylammonium hydroxide (TTAOH) and lauric acid (LA). The H+ and OH- counterions form water (TTAOH+LA-->TTAL+H2O), leaving the solution salt-free. The phase behaviors at fixing the total surfactant concentration (cTTAL) to be 33.0 and 55.0 mmol L(-1), respectively, were studied through varying the molar ratio of r=nLA/nTTAOH from 0.70 to 1.20. With an increasing value of r, one observed an L1-region, an Lalpha/L1 two-phase region with a birefringent Lalpha-phase at the top, and finally a single Lalpha-phase. The ability to solubilize a fullerene mixture of C60 and C70 of different phases in different regions was tested. The colloidal stability and phase behavior of different phases with embedded fullerenes were investigated as a function of r, cTTAL, and weight ratio of fullerene to surfactant (WF/WTTAL). The 33.0 or 55.0 mmol L(-1) zero-charged vesicle-phase at r=1.00 could solubilize a considerable amount of fullerenes without macroscopic phase separation and obvious vesicular structure breakage. However, these colloidal solutions became unstable at lower concentrations of surfactants, and a precipitate would be observed at the bottom. The micellar (L1-phase) solubilization at the TTAOH-rich side was less pronounced compared to the vesicular solubilization of the zero-charged vesicle-phase, and the solubilizing ability decreased at higher r values. In the Lalpha/L1 two-phase region, a brown or dark-brown Lalpha-phase was usually found at the top of a colorless or yellowish L1-phase, indicating that most of the fullerenes were embedded in the upper Lalpha-phase. The influence of fullerene incorporation on the property of the zero-charged TTAL vesicle-phase was also investigated, and evidence has been found that the system tended to be more fluid after fullerenes were incorporated into the hydrophobic microdomains of aggregates.     

Overlapping of three-phase regions in a water/nonionic surfactant/triglyceride system

It was found that two types of three-phase regions containing surfactant phases (microemulsions) are overlapped and the four coexisting phases including excess water and oil phases appear in a three-component system of water/hexaethyleneglycol tetradecyl ether (R₁₄EO₆)/triglyceride (1,2,3-[tris(2-ethylhexanoyloxy)] propane, TEH). A schematic diagram of three- and four-phase behavior was constructed based on the real phase diagrams. One type of three-phase behavior is the same as that typically appearing over a wide range of water/oil ratios in a water/nonionic surfactant/hydrocarbon system. The other type of three-phase behavior is similar to that observed over a wide range of water/oil ratios in a system of water/nonionic surfactant/amphiphilic oil such as long-chain alcohols, fatty acids, and triglycerides. The result clearly shows how two three-phase regions interact with each other and are transferred from one to another.     

Novel viscoelastic systems from cationic surfactants and hydrophobic counter-ions: influence of surfactant chain length

In continuation of our previous investigations on the aqueous phase behavior of cetyltrimethylammonium 2-hydroxy-1-carboxy-naphthoate (CTA-2,1-HCN) (see J. Colloid Interface Sci. 288 (2005) 570), we have studied the phase behavior and the properties of the phases of the two shorter homologues, C(14)TA-2,1-HCN and C(12)TA-2,1-HCN. The phases were prepared from the alkyltrimethylammonium hydroxides RTAOH and the naphtholcarboxylic acid. By preparing the systems in this way the surfactant solutions contain no excess salt. With increasing counter-ion-surfactant ratio r we observed the same sequence of phases as for the previously studied C(16)-system, namely a L(1)-phase and a L(alpha)-phase with multilamellar vesicles (MLV). The single phases are separated by a two-phase L(1)/L(alpha) region. The phases were characterized with FF-TEM, rheological and SANS measurements. For both systems the viscosity of the L(1)-phases passes with increasing counter-ion/surfactant ratio over a maximum. The height of the maximum decreases strongly with decreasing chain length while the complex viscosity of the MLV-phase depends little on the chain length. For 100 mM solution both MLV phases behave like a weak gel and have a yield stress value. It is thus shown that it is possible to prepare viscoelastic surfactant solutions with a yield stress value from single chain surfactants with a dodecyl chain.     

新型农药丙酯草醚对微乳液体系相行为的影响

表面活性剂;微乳液;“鱼形”相图;丙酯草醚     

Self-assembly in mixed dialkyl chain cationic-nonionic surfactant mixtures: dihexadecyldimethyl ammonium bromide-monododecyl hexaethylene glycol (monododecyl dodecaethylene glycol) mixtures

The self-assembly of dialkyl chain cationic surfactant dihexadecyldimethyl ammonium bromide, DHDAB, and nonionic surfactants monododecyl hexaethylene glycol, C(12)E(6), and monododecyl dodecaethylene glycol, C(12)E(12), mixtures has been studied using predominantly small-angle neutron scattering, SANS. The scattering data have been used to produce a detailed phase diagram for the two surfactant mixtures and to quantify the microstructure in the different regions of the phase diagram. For cationic-surfactant-rich compositions, the microstructure is in the form of bilamellar, blv, or multilamellar, mlv, vesicles at low surfactant concentrations and is in an L(beta) lamellar phase at higher surfactant concentrations. For nonionic-rich compositions, the microstructure is predominantly in the form of relatively small globular mixed surfactant micelles, L(1). At intermediate compositions, there is an extensive mixed (blv/mlv) L(beta)/L(1) region. Although broadly similar, in detail there are significant differences in the phase behavior of DHDAB/C(12)E(6) and DHDAB/C(12)E(12) as a result of the increasing curvature associated with C(12)E(12) aggregates compared to that of C 12E 6 aggregates. For the DHDAB/C(12)E(12) mixture, the mixed (blv/mlv) L(beta)/L(1) phase region is more extensive. Furthermore, C(12)E(12) has a greater impact upon the rigidity of the bilayer in the blv, mlv, and L(beta) regions than is the case for C(12)E(6). The general features of the phase behavior are also reminiscent of that observed in phospholipid/surfactant mixtures and other related systems.     

Determination of the Phase Inversion Temperature of Orange Oil/Water Emulsions by Rheology and Microcalorimetry

Abstract

In low-energy emulsification processes, phase inversion occurs when the phases of a dispersion exchange, because of changes in the medium's properties. This paper reports experiments to determine the phase inversion temperature (PIT) of orange oil/water emulsions stabilized by nonionic surfactants. Two techniques were employed: rheology, which is already commonly used to obtain the PIT, and microcalorimetry, which has been proposed as a new technique. Continuous monitoring of the emulsions' viscosity permitted identifying different phenomena that occur while the temperature varies. For all the dispersions prepared, the rheological curves obtained showed two peaks, one attributed to the phase separation process and the other to the phase inversion phenomenon. The microcalorimetry technique showed two endothermic transitions as the dispersion's temperature increased. The initial temperatures were comparable to those obtained by rheology. The influence of the surfactant concentration and the hydrophilic-lipophilic balance (HLB) of the mixture of surfactants and the reduction in volume of the phases at the phase inversion temperature were also evaluated. In general, both methods used to evaluate the phase inversion of the orange oil/water systems (rheology and microcalorimetry) presented concordant results, both for the phase separation process and the phase inversion temperature.     

The Effect of Fluctuations on Bilayer and Monolayer Systems: High-Resolution X-ray Scattering Study of a Three-Component Lamellar Phase

We have investigated the effect of symmetry on the fluctuation of a three-component lamellar phase composed of oil (octane), water, and a nonionic surfactant (C12E5). The studied lamellae consist of various oil/water volume ratios for a fixed surfactant concentration. From aligned lamellae, we succeeded in obtaining highly reproducible, high-resolution X-ray spectra with very small full width at half maximum (6 × 10⁻⁴Å⁻¹). The deviation of the periodicity expected by the dilution law can be explained from the fluctuations. Measuring this deviation, we observed that for the constant surfactant concentration, lamellae with equal oil/water ratios have higher fluctuation than when oil/water → 0 or ∞ because of the difference of the flexibility of monolayers and bilayers     

Computer simulation studies of surfactant monolayer mixtures at the water/oil interface: charge distribution effects

Charge distribution effects on polar head groups for a mixture of amphiphilic molecules at the water/oil interface were studied. For this purpose a model which allowed us to investigate the charge effects exclusively was created. As a molecular model we used the structure of sodium dodecyl sulfate. Then we prepared molecules with the same molecular structure but with different charge distributions in order to have one cationic and one nonionic molecule. So, in this way, we were able to focus only in the charge effects. The monolayer mixtures were composed of anionic/nonionic and cationic/nonionic surfactants. Simulations of these systems show that the location of the different surfactants at the interface is determined by the interaction and the charge distribution of the molecules. Due to the difference in the charge distribution of the surfactant monolayers, the water molecules present distinct orientations in the mixture. Finally, it was found that the electrostatic potential difference across the interface depended on the interactions (charge distribution) of the anionic, cationic, and nonionic molecules in the mixture.     

Structural evolution in the isotropic channel of a water-nonionic surfactant system that has a disconnected lamellar phase: a 1H NMR self-diffusion study

We showed in a previous study that a water-nonionic surfactant system, where the surfactant is a 9:1 mixture of tetraethylene glycol monodecyl ether (C(10)E(4)) and pentaethylene glycol monodecyl ether (C(10)E(5)), forms a disconnected lamellar (L(α)) phase. Thus, the isotropic phase spans the whole concentration range from the water-rich L(1) region to the surfactant-rich L(2) region of the phase diagram. The L(1) and L(2) regions are connected via an isotropic channel that separates the two regions of the L(α) phase. In this letter, we monitored the structural evolution of the isotropic phase along a path through this isotropic channel via (1)H NMR self-diffusion measurements. We used this technique because it enables us to distinguish between discrete and bicontinuous structures by comparing the relative self-diffusion coefficients (obstruction factors) D/D(0) of the solvents (i.e. of water and surfactant in the present case). We found that the obstruction factor of water decreases whereas the obstruction factor of the surfactant increases with increasing surfactant concentration and increasing temperature. This trend is interpreted as the transition from a water-continuous L(1) region, which contains discrete micelles, to a bicontinuous structure, which may extend to very high surfactant concentrations. Although there is good evidence of bicontinuity over a broad concentration range, there is no evidence of inverse micelles or any other microstructure at the highest concentration studied in the surfactant-rich L(2) phase.     

Microemulsions with alkyldimethyl phosphine oxides and alkyldiethyl phosphine oxides

Alkyldimethyl phosphine oxides (C n DMPO) as well as alkyldiethyl phosphine oxides (C n DEPO) with chain lengths of n = 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) were synthesized and purified to study how the formation of microemulsions depends on the size of the headgroup and on the length of the alkyl chain. For that purpose, equal amounts of water and n-octane were taken and surfactant was added to solubilize the two solvents. The resulting fish-shaped phase diagrams for C 10DEPO, C 12DEPO, and C 14DEPO show that the longer the hydrophobic chain the more efficient the surfactant. Simultaneously, the extension of the lamellar phase (L alpha) shifts toward lower total mass fractions gamma of the surfactant, i.e., the tendency to form lyotropic liquid crystals (LCs) increases. These trends are well-known for nonionic alkyl ethylene oxides and can thus be interpreted accordingly. What is astonishing, however, is the significant influence the size of the short side chains has. Replacing two methyl groups by two ethyl groups leads to a drastic drop of the three-phase region toward lower temperatures, while the efficiency remains nearly unchanged. Moreover, the tendency to form LCs decreases significantly.     

Glycerol-induced swollen lamellar phases with siloxane copolymers

Phase behavior is established for a block copolymer polyethyleneoxide-b-dimethylsiloxane-polyethylenoxide (EO)(15)-(PDMS)(15)-(EO)(15) (IM-22) a in glycerol/water mixed solvent. In water alone, the block copolymer forms biphasic micellar/lamellar (L(1)/L(alpha)) systems over the range 10-70 wt%, with single L(alpha)-phases between 70-90 wt%. Strong solvent effects on the phase behavior were noted. For example, using a mixed 60:40 vol% glycerol/water solvent, the single L(alpha)-phase region appears at much lower concentrations, only 20 wt% IM-22, as compared to the biphasic L(1)/L(alpha) system observed in water alone. This interesting observation of L(alpha)-phase swelling on addition of glycerol may be explained by a decrease in attraction between the bilayers, as it is also found that in this mixed glycerol/water solvent there is a close refractive index matching with IM-22. Rheological measurements show the L(alpha)-phases with added glycerol have low shear moduli. The influence of added ionic surfactant sodium dodecylsulfate (SDS) on these swollen IM-22 L(alpha)-phases was studied. Small-angle X-ray scattering (SAXS) indicated the interlamellar distance d remains essentially constant up to 3 mM SDS, and then decreases with increasing SDS content. This weak effect is consistent with the fact that the L(alpha)-phases are most swollen when the mixed solvent contains 60 vol% glycerol. The results suggest that glycerol/water solvent mixtures can be used to tune the refractive index of the background solvent, modifying DLVO-type interactions, and causing significant effects on the phase stability of simple block-copolymer systems.     

Determining scaling in known phase diagrams of nonionic microemulsions to aid constructing unknown

Microemulsions based on nonionic surfactants of the ethylene oxide alkyl ether type C_mE_n, have been studied thoroughly for around 30 years. Thanks to the considerable amount of published data available on these systems, it is possible to observe trends to make predictions of phase diagrams not yet determined. Strey and Kahlweit, and subsequently Sottmann and Strey, with coworkers have studied and published phase diagrams for systems with a fixed ratio of oil to water, varying the surfactant, the so-called Kahlweit fish-cut diagrams. Some properties of the phase diagrams can be scaled to become general and not system dependent. Here are shown two examples of scaling data from phase diagrams and the use of trends to determine phase diagrams, both inside and outside a dataset. The trends of microemulsions with fixed ratio of surfactant to oil, the so-called Lund-cut diagrams, are also investigated. The trends are used to determine a new phase diagram and this is compared with previously unpublished experimental data on C₁₂E₅-Octadecane-Water system. The scalings and trends make it possible to get good estimations of many of the important properties of the phase diagrams, both temperatures and surfactant concentrations of interest, by investigating one sample in the 3-phase region of the balanced fish-cut diagram.     

The importance of lipophobicity in surfactants: methods for measuring lipophobicity and its effect on the properties of two types of nonionic surfactant

In researching the properties of surfactants, lipophobicity is an important consideration. Increasing surfactant lipophobicity corresponds to a decrease in the saturation concentration of a singly dispersed surfactant in oil, i.e., a decrease in the critical micelle concentration in oil (CMC(oil)). This, in turn, is the crucial property in discussing the efficiency of a surfactant. Lipophobicity is influenced by the structure and length of the hydrophilic moiety of the surfactant. Surfactants that consist of OH or CO groups are effective for use in both aliphatic and aromatic hydrocarbon-rich systems because they are highly lipophobic and of a compact size and function independent of temperature. These characteristics are also reflected in their phase behavior. Phase diagrams illustrate the following properties: temperature independence; strong absorption at the water-oil interface and efficient action even with a very small amount of surfactant with a low CMC; high solubilization of water and oil into an aggregated surfactant solution phase. Through phase diagrams, the CMC(oil) of R10EO8 was obtained and the result used to compare the many different characteristics of the more typical oxyethylene nonionic surfactants with the new polyglyceryl nonionic surfactants.     

Phase behavior of monoglycerol fatty acid esters in nonpolar oils: reverse rodlike micelles at elevated temperatures

We have studied nonaqueous phase behavior and self-assemblies of monoglycerol fatty acid esters having different alkyl chain lengths in different nonpolar oils, namely, liquid paraffin (LP 70), squalane, and squalene. At lower temperatures, oil and solid surfactants do not mix at all compositions of mixing. Upon an increase in the temperature of the surfactant system, the solid melts to give isotropic single or two-liquid phases, depending on the nature of the oil and the surfactant. All monolaurin/oil systems form an isotropic single-phase liquid, but with a decreasing alkyl chain length of surfactant, they become less lipophilic and immiscible in oils. As a result, a two-phase domain is observed in the oil rich region of all monocaprylin/oil systems over a wide range of concentrations. Judging from the phase diagrams, the surfactants are the least miscible with squalane, and the order of miscibility tendency is squalene > LP 70 > squalane. With a further increase of temperature, the solubility of the surfactant in the oil increases, and the two-liquid phase transforms to an isotropic single phase. This phase transformation corresponds to the reverse of the cloud-point phenomenon observed in aqueous nonionic surfactant systems. Small-angle X-ray scattering (SAXS) measurements show the presence of reversed rodlike micelles in the isotropic single phase, and the length of the aggregates decreases with increasing temperature and increasing alkyl chain length of the surfactant. These results indicate a rod-sphere transformation with increasing lipophilicity of the surfactant and confirms the validity of Ninham's penetration model in the reversed system. An addition of a small amount of water dramatically enhances the elongation of the reverse micelles. Increasing the surfactant concentration or changing the oil from squalene to LP 70 also increases the length of the rodlike aggregates.     

Effect of salts on the phase behavior and the stability of nanoemulsions with rapeseed oil and an extended surfactant

For many decades, the solubilization of long-chain triglycerides in water has been a challenge. A new class of amphiphiles has been created to overcome this solubilization problem. The so-called "extended" surfactants contain a hydrophilic-lipophilic linker to reduce the contrast between the surfactant-water and surfactant-oil interfaces. In the present contribution, the effects of different anions and cations on the phase behavior of a mixture containing an extended surfactant (X-AES), a hydrotrope (sodium xylene sulfonate, SXS), water, and rapeseed oil were determined as a function of temperature. Nanoemulsions were obtained and characterized by conductivity measurements, light scattering, and optical microscopy. All salting-out salts show a transition from a clear region (O/W nanoemulsion), to a lamellar liquid crystalline phase region, a clear phase (bicontinuous L(3)), and again to a lamellar liquid crystalline phase region with increasing temperature. For the phase diagrams with NaSCN and Na(2)SO(4), only one clear region (O/W nanoemulsion) was observed, which turns into a lamellar phase region at elevated temperatures. Furthermore, the stability of the nanoemulsions was investigated by time-dependent measurements: the visual observation of phase separation, droplet size by dynamic light scattering (DLS), and optical microscopy. The mechanism of the different phase transitions is also discussed.