Hydrophile-lipophile Balance Temperature Research Articles

Preparation of stable inverse emulsions of hydroxyethyl methacrylate and their stability evaluation by centrifugal coefficient

Several inverse emulsions were prepared with different hydrophilic-lipophilic balance (HLB) values using different water/oil ratios, temperatures and monomer and emulsifier concentrations by uniform stirring for more than 30 min. The stability of inverse emulsion was characterized by centrifugal coefficient. The emulsion form, either oil/water (O/W) or water/oil (W/O) was characterized by optical microscope and conductivity measurements. The results showed that HLB value, water/oil ratio and temperature could have an effect on the emulsion stability and emulsion form. When the HLB value of emulsifier is about 8.4, the water to oil ratio is about 1:1 and the temperature is at about 25 °C, inverse emulsion in the form of water in oil (W/O) was found to be the most stable. Here, the stablilty of emulsions was studied in relation to temperature and we found that 25 °C (room temperature) is the best for obtaining the most stable inverse emulsion, which is also most suitable for the redox initiation in this system. In the present study, we showed that temperature has a significant influence on the structure morphology and stability of inverse emulsion and hence, it is necessary to select the appropriate reaction temperature for inverse emulsion polymerization. This is a novel result. A decrease of the content of hydroxyethyl methacrylate in aqueous solution with an increase of emulsifier concentration in emulsion was found to elevate the stability of inverse emulsion. The addition of trace electrolytes in the emulsion, however, led to greatly reduced stability of the inverse emulsion.

On the Relationships between the Hydrophilic–Lipophilic Balance and the Nanoarchitecture of Nonionic Surfactant Systems

AbstractBuilding links between established parameters for the characterization of surfactant systems is useful not only for the understanding of the underlying phenomena but also for the judicious formulation of products. Herein, we review comprehensively the literature data to find correlations between the hydrophilic–lipophilic balance (HLB) and the molecular packing parameter (CPP) for a variety of nonionic surfactants in water. The interfacial area per surfactant molecule, a fundamental variable to calculate CPP, follows a power law as a function of the number of ethylene oxide (EO) groups in the surfactant. The exponent ranges from 0.3 to 0.7, which may reflect changes in the conformation of the EO chain depending on the nature of the hydrophobic group; there is also apparently a transition toward a collapsed conformation of the EO chains at high surfactant concentrations. CPP is found to change linearly with HLB in the range of data studied, although the parameters of the linear fitting depend on the nature of both hydrophobic and hydrophilic moieties of the surfactant; this would also imply a linear relationship between CPP and the HLB temperature (i.e., Phase Inversion Temperature) according to the Kunieda–Shinoda equation. Analysis of the liquid crystal regions of the surfactant phase diagram at constant temperature indicates that the HLB values required for the morphological phase transitions defined by CPP increase with surfactant concentration. The present report may serve as a contribution to the programmed design of nanoarchitectures in surfactant systems.

Optimization of water-in-oil nanoemulsions by mixed surfactants

The formation of water-in-oil (W/O) nanoemulsions in isohexadecane/mixed nonionic surfactant/water system has been achieved by a low-energy emulsification. Effects of polyoxyethylene 2-lauryl ether (C 12E 2) and polyoxyethylene 4-lauryl ether (C 12E 4) on the water in isohexadecane emulsions were systematically studied. Ratios of the two-surfactant mixture, surfactant concentrations, and oil fraction were evaluated by gauging droplet size with the aid of photon correlation spectroscopy. Hydrophilic–lipophilic balance temperature ( T HLB) and phase diagram were used to characterize the nanoemulsion system. The stability of the emulsions prepared was assessed based on the change in droplet size as a function of time. Instability mechanisms including coalescence and Ostwald ripening for the nanoemulsion system are discussed. The addition of a second surfactant could provide more stable nanoemulsions with the minimum size than only one surfactant. Finally, a nanoemulsion composition was optimized and found to be highly stable over a 200-day storage period. The optimum composition for W/O nanoemulsion is isohexadecane/C 12E 2/C 12E 4/water 70:6:4:20 wt%.

Phase behavior of the mixtures of poly(oxyethylene) (10) stearyl ether (Brij-76), 1-butanol, isooctane, and mixed polar solvents: II. Water and ethylene glycol (EG) or tetraethylene glycol (TEG)

The phase diagrams of the pseudo-quaternary systems poly(oxyethylene) (10) stearyl ether (Brij-76)/1-butanol/isooctane/water (with equal amounts of oil and water in the presence of two nonaqueous polar solvents (NPS), ethylene glycol (EG), and tetraethylene glycol (TEG)), have been constructed at 30 °C. Regular fish-tail diagrams were obtained up to ψ (weight fraction of EG or TEG in the mixture of polar solvents) equal to 0.5, confirming the establishment of hydrophile–lipophile balance (HLB) of the systems. The maximum solubilization capacity passed through a minimum at ψ = 0.2 . No HLB was obtained at higher ψ. The usual fish-tail diagrams were also obtained in temperature-induced phase mapping at fixed W 1 (weight fraction of 1-butanol in total amphiphile). Solubilization capacity and HLB temperature ( T HLB ) decreased with increasing ψ at a fixed W 1 , the effect being more pronounced for TEG than EG. A correlation between HLB temperature ( T HLB ) and HLB number ( N HLB ) of mixed amphiphiles (Brij-76 + Bu) in pseudo-quaternary systems (in the presence of water and partial substitution of water with both NPS) has been established. The novelty of the work with respect to possible applications has been discussed.

Phase behavior and nano-emulsion formation by the phase inversion temperature method.

Formation of oil-in-water nano-emulsions has been studied in the water/C12E4/isohexadecane system by the phase inversion temperature emulsification method. Emulsification started at the corresponding hydrophilic-lipophilic balance temperature, and then the samples were quickly cooled to 25 degrees C. The influence of phase behavior on nano-emulsion droplet size and stability has been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the smallest droplet sizes were produced in samples where the emulsification started in a bicontinuous microemulsion (D) phase region or in a two-phase region consisting of a microemulsion (D) and a liquid crystalline phase (L(alpha)). Although the breakdown process of nano-emulsions could be attributed to the oil transference from the smaller to the bigger droplets, the increase in instability found with the increase in surfactant concentration may be related to the higher surfactant excess, favoring the oil micellar transport between the emulsion droplets.

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.

A Study of the Relation between Bicontinuous Microemulsions and Oil/Water Nano-emulsion Formation

Oil/water (O/W) nano-emulsions have been formed in the system water/C16E6/mineral oil by the phase inversion temperature (PIT) method. The relation between the phase equilibria observed at the hydrophilic−lipophilic balance (HLB) temperature or the PIT (i.e., the nature, number, and relative volume fractions of the involved phases), the droplet sizes, and polydispersities of the resulting emulsions have been determined. Milky white emulsions were obtained when, at the HLB temperature, a three-phase equilibrium formed by water (W), shear-birefringent microemulsion (D), and oil (O) was observed. However, bluish transparent O/W nano-emulsions with droplet sizes as low as 40 nm were formed in a narrow range of oil-to-surfactant ratios in which a D or W + D phases were the initial equilibrium phases. In the W + D equilibria, droplet sizes were independent from the water content, indicating that nanodroplet formation is mainly controlled by the structure of the D phase. These results suggest that the main requirement for bluish transparent O/W nano-emulsion formation is the complete solubilization of the oil component in a bicontinuous microemulsion, independent of whether the initial phase equilibrium is single or multiphase.

Enzymatic Carbon−Carbon Bond Formation in Water-in-Oil Highly Concentrated Emulsions (Gel Emulsions)

Water-in-oil (W/O) highly concentrated emulsions (gel emulsions) of water/C 1 4 E 4 /aliphatic hydrocarbon systems were investigated as reaction media for the aldolic condensation of dihydroxyacetone phosphate (DHAP) with acceptor aldehydes such as phenylacetaldehyde (1) and benzyloxyacetaldehyde (2), catalyzed by D-fructose-1,6-bisphosphate aldolase from rabbit muscle (RAMA). Prior to any enzymatic reaction, both the formation and stability of the W/O gel emulsions in the presence of reactants were assessed. It was found that the aldehydes improved greatly the kinetic stability of W/O gel emulsions at 25 °C by decreasing the hydrophile-lipophile balance temperature (T H L B ) of the water/C 1 4 E 4 /aliphatic hydrocarbon systems. Interestingly, the stability of RAMA in W/O gel emulsions was improved by 7- and 25-fold compared to that in aqueous medium or conventional dimethylformamide/water 1/4 v/v mixture, respectively. It was found that the equilibrium yields and enzymatic activity depended on both the aldehyde partitioning between the continuous and dispersed phases and the water-oil interfacial tension. The highest enzymatic activities were achieved in W/O gel emulsion systems with the lowest water-oil interfacial tension. The equilibrium yield depended on the water-oil interfacial tension for the hydrophobic phenylacetaldehyde, and on the partition coefficient for the hydrophilic benzyloxyacetaldehyde. Optimum equilibrium product yields (65-70%) were achieved at either the lowest water-oil interfacial tension or partition coefficient values.

Formation and Stability of Nano-Emulsions Prepared Using the Phase Inversion Temperature Method

Formation of O/W nano-emulsions has been studied in water/C̄12Ē4/oil systems by the phase inversion temperature emulsification method. Emulsification was carried out at the corresponding HLB (hydrophilic−lipophilic balance) temperature, and then the emulsions were cooled fast to 25 °C. The influence of surfactant concentration and oil solubility on HLB temperature, nano-emulsion droplet size, and stability has also been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the breakdown process of nano-emulsions studied could be attributed to Ostwald ripening. An increase of nano-emulsion instability with the increase in surfactant concentration and oil solubility was also found.

Solubilization Enhancing Effect of A-B-Type Silicone Surfactants in Microemulsions

We report a solubilization enhancing effect of A-B-type silicone surfactants in microemulsions. The effect of added long-chain silicone surfactants, Si25C3EO51.6 (extended length≈21.8 nm) and Si14C3EO15.8 (extended length≈8.5 nm) on the solubilization capacity of C12EO5 (extended length≈3 nm)/water/dodecane microemulsion was investigated at the hydrophile-lipophile balance temperature at which a microemulsion (surfactant) phase containing equal weights of oil and water touches the three-phase body. The addition of silicone surfactants exhibits an enormous increase of the swelling of the middle phase primarily with an associated increase in the structural length scale of the microemulsion. The solubilization power increases with increasing x2 (mole fraction of silicone surfactants to the total surfactant) and going through a maximum it decreases, since a lamellar liquid crystal introduces in the multiphase region at low surfactant concentrations. The solubilization capacity reaches at the maximum to an almost equal level for different x2 values, 0.02 for Si25C3EO51.6 and 0.09 for Si14C3EO15.8. The solubilization power of the lamellar phase shows a similar trend with lower magnitude.

Clipped random wave analysis of anisometric lamellar microemulsions.

Small-angle neutron scattering experiments were performed on C10E4-D2O-octane (where C10E4 is tetraethylene glycol monodecyl ether) anisometric microemulsions in the lamellar phase at a constant surfactant volume fraction of 20% and at the hydrophile-lipophile balance temperature of 22.5 degrees C. The results were analyzed using a clipped random wave model with a specific spectral distribution function developed by us previously. This enabled us to generate three-dimensional morphologies of the microemulsions, which showed clearly that in sufficiently anisometric microemulsions the oil-water interface was no longer connected. At large anisometry isolated regions of oil or water were found, and the transition from a bicontinuous structure at isometry to these isolated micelles far from isometry goes through an intermediate cylindrical morphology when the oil-to-water or water-to-oil ratio is around 4 to 1. We further computed the joint distribution function of the mean curvature H and Gaussian curvature K of the entire oil-water interface for each anisometric microemulsion. In particular, we show the distribution of <H>, <K>, and <H2>-<H>(2) for different isolated regions within an oil-rich microemulsion at an oil-to-water ratio of 85% to 15%. These distributions allowed us to prove that the isolated regions formed in highly anisometric microemulsions were small and had spherical topology.

Clipped random wave analysis of isometric lamellar microemulsions

We have made small angle neutron scattering studies of C10E4-D2O-octane isometric microemulsions in the lamellar phase at the hydrophile-lipophile balance temperature. The scattering intensity distributions were then analyzed with a particular choice of a spectral density function (SDF) derived by maximization of generalized entropy. The model agrees well with the measured intensities on an absolute scale, and allowed us to derive various length scales associated with the microemulsion mesoscopic structure as well as the average interfacial curvatures. We also used the experimentally determined SDF to generate a three-dimensional snapshot of the fluctuating microemulsion microstructure. Unlike conventional pictures of extended lamellar planes, we observed small domains which were internally lamellar but randomly oriented with respect to each other. Finally, we computed the probability distributions of the mean curvature H and the Gaussian curvature K on the oil-water interface. The former showed a symmetric distribution centered around H = 0, while the latter showed a skewed distribution peaked at a negative value of K, but with a wing extending to positive values.

Effect of Types of Perfume Compounds on the Hydrophile–Lipophile Balance Temperature

The effect of added perfume compounds (d-limonene (LN), α-hexylcinnamic aldehyde (HCA), β-ionone (IN), benzyl acetate (BA), linalool (LL), geraniol (GL), eugenol (EL), and cis-3-hexenol (HL)) on the three-phase behavior was investigated in water/octaethylene glycol dodecyl ether (C12EO8)/perfume compound systems. The HLB (hydrophile–lipophile balance) temperatures are considerably lower than those of saturated hydrocarbon systems and are in the order LN > HCA > IN > BA > LL > GL > EL > HL. It is considered that the perfume molecules tend to be solubilized in the vicinity of the interface of the water–hydrocarbon moieties of the surfactant or the surfactant palisade layer. To confirm this, the location of the solubilized perfume compound in aggregates of liquid crystals was investigated by small-angle X-ray scattering (SAXS). In the LN, HCA, IN, BA, LL, and GL systems, the hexagonal liquid crystalline phase changes to lamellar liquid crystals on addition of each perfume compound, whereas the hexagonal liquid crystalline phase is directly changed to a reverse micellar solution phase in the EL and HL systems. The effective cross-sectional area per surfactant molecule, as, was calculated by using interlayer spacing measured by SAXS. Perfume compounds, which reduce the HLB temperature greatly, tend to penetrate into the surfactant palisade layer and increase as. Thus, the perfume molecules change the surfactant curvature from positive to negative. The more the perfume compound penetrates into the palisade layer, the lower the HLB temperature becomes.

The Gaussian curvature of the oil-water interface in an isometric bicontinuous microemulsion

Small-angle neutron scattering (SANS) measurements are made on a three-component isometric (equal volume fractions of water and oil) microemulsion system, composed of AOT/water (0.4% NaCl)/D-octane, in the one-phase channel near the three-phase region at and around the hydrophile-lipophile balance temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion is bicontinuous in water and oil with the surfactant film at the interface having a zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function appropriate for the microemulsion system. The model analysis results in good agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the average Gaussian curvature of the interface. We discuss the variation of the average Gaussian curvature as a function of the surfactant volume fraction and its implication on the degree of local order of the bicontinuous structure. We also show a 3-D reconstructed morphology of the most disordered microemulsion.

Measurement of the Gaussian curvature of the surfactant film in an isometric bicontinuous one-phase microemulsion.

Small-angle x-ray and neutron-scattering (SAXS and SANS) measurements are made of a three-component isometric microemulsion, ${\mathrm{C}}_{10}$${\mathrm{E}}_{4}$-${\mathrm{D}}_{2}$O-octane, in the one-phase channel around the hydrophile-lipophile balance temperature of the system. A previous SANS contrast variation experiment indicated that the microstructure of this isometric microemulsion is bicontinuous in water and oil, with the surfactant film having a zero mean curvature. We analyze the SAXS and SANS data taken with a bulk contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters $a$, $b$, and $c$, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the microemulsion. The analysis gives an excellent agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the mean Gaussian curvature of the surfactant film. We also show a three-dimensional-reconstructed morphology of the microemulsion.

The Effect of Mixing of Surfactants on Solubilization in a Microemulsion System

The effect of mixing homogeneous polyethylene glycol alkyl ethers (R m EO n ) on their maximum solubilizing power was investigated at the hydrophile-lipophile balance (HLB) temperature at which a microemulsion (surfactant) containing equal weights of water and oil is one phase of a three-phase body. The solubilization was compared at a fixed temperature equal to the HLB temperature for a single R 12EO 5 system. It was found that the minimum weight fraction of surfactant required to solubilize equal weights of water and oil into a single phase ( X b ) is decreased by mixing R 12EO 2 and R 12EO 8 or R 14EO 5and R 10EO 5. However, X b for the R 12OH-R 12EO 8 system is larger than for the R 12EO 2-R 12EO 8 system. Namely, the solubilization apparently reaches its maximum in a mixed surfactant system in which the hydrophilic-lipophilic properties of the surfactants are not very different. Nonionic surfactant is mainly distributed between oil microdomains and the interface between oil and water microdomains inside the microemulsion phase. Assuming that the monomeric solubility of each surfactant component in oil is the same as in the oil microdomain of the microemulsion, the weight fraction of each surfactant at the interface in the microemulsion ( C or C 1 ) was obtained. C or C 1 + C 2 indicates the real solubilizing power, and it is dramatically decreased when surfactants are mixed. The more the HLBs of the surfactants are separated, the more the real solubilizing power is increased. It was also found that the mixing ratio of surfactants at the water-oil interface inside the microemulsion phase is directly related to the HLB temperature.

Factors determining emulsion type: Hydrophile—lipophile balance and beyond

Bancroft's rule of thumb that a surfactant which preferentially partitions into water favors the formation of oil-in-water (O/W) emulsions and that a surfactant which preferentially partitions into oil favors the formation of water-in-oil (W/O) emulsions has been known for some 80 years. Although by judicious control of the emulsification process one can generate exceptions, the rule of thumb often works well. It was not, however, until Griffin's famous paper of 1949 that an attempt was made to quantify the emulsifying tendency of a surfactant. Griffin observed that certain combinations of the surfactant hydrocarbon and ethylene oxide chain lengths favored O/W or W/O emulsions. In the paper he noted that the emulsion chemist will choose a water-soluble surfactant to make an O/W emulsion and an oil-soluble one to make a W/O emulsion. To try to put this principle of hydrophile—lipophile balance (HLB) on a quantitative footing, he introduced the concept of an HLB number. According to Griffin, the HLB is the balance of the size and strength of the hydrophilic and lipophilic moieties of a surfactant molecule. The HLB number was based on the molecular groups composing the surfactant. According to this concept, the optimal surfactant for a desired emulsion of a given oil can be chosen by a simple calculation from a look-up table. A problem with the HLB concept was that the HLB numbers were based on ambient temperature data. A given ethoxylated hydrocarbon can form in O/W emulsions at room temperature while it gives W/O emulsions at higher temperatures. Thus the HLB cannot be related solely to the molecular groups of the surfactant. Temperature and interactions with the aqueous and oil phases have to be incorporated into the HLB number if it is to be a predictive tool. There is a strong correlation between whether an O/W emulsion or a W/O emulsion is formed and whether the surfactant tends to form an aqueous micellar phase or an oil-rich inverted micellar phase. Thus, as preferred by Becher, relating the HLB number to the free energies of micellization in water and oil phases ought to result in a more predictive tool. Shinoda and co-workers assert that it is preferable to introduce an HLB temperature based on the phase inversion temperature (PIT). This temperature is a property of the surfactant—oil—water phase diagram. For non-ionics, the PIT is the temperature below which a surfactant partitions preferentially into the water phase as oil-swollen micelles and above which it partitions preferentially into the oil phase as water-swollen inverted micelles. The advantage of basing the HLB on the PIT is that the surfactant—oil—water interactions are automatically incorporated into the HLB criterion. Similarly, the effect of cosurfactants, frequently needed for stable emulsions, is accounted for as a shift in the PIT. Finally, basing the HLB temperature on the PIT admits the strong correlation between emulsion type and ternary or pseudoternary phase behavior. We explore here the connection between the generic ternary phase behavior and emulsification tendencies and arrive at a generalization of Shinoda's PIT criterion. The trend from preferential partitioning of surfactant into the aqueous phase to a balanced or optimal microemulsion (equal uptake of oil and water) to preferential partitioning into the oil phase can be accomplished by a large number of variables (e.g. the field variables temperature, salinity and alcohol activity, and the extended field variables such as the average carbon number of the oil, the average carbon number of the hydrophobic moiety of the surfactant, the average number of ethylene oxide groups of the hydrophilic moiety of the surfactant, etc.) for the various types of surfactant. The field variable at which the optimal microemulsion occurs provides an optimal point (OP) that can serve as the HLB for a given system. If the field variable is set on one side (above or below depending on the variable) of the OP for a system, the surfactant serves as a hydrophilic agent (favors O/W emulsions) and if it is set on the other side of the OP, the surfactant serves as a hydrophobic agent (favors W/O emulsions). Since an optimal point can be achieved by variation of many parameters and field variables, the optimal microemulsion, and thus the HLB, is defined by a hypersurface in the space spanned by these variables. We also discuss the relationship between generic phase behavior of surfactant, oil and water systems and the curvature properties of surfactant interfacial films in association colloids.

ESR study on the stability of W/O gel-emulsions

W/O gel-emulsions (high-internal-phase-volume-ratio emulsions) form in water (or brine) /tetraethyleneglycol dodecyl ether/heptane system above the HLB (hydrophile-lipophile balance) temperature of the system. A salt, which largely decreases cloud temperature in a water-nonionic surfactant system, makes the surfactant film rigid and the gel-emulsions hence become very stable. The effect of aded salt on the apparent order parameter “S”, and the isotropic hyperfine splitting constant “aN” in gel-emulsions was determined by the ESR spin probe method using 5-doxyl stearic acid as the spin probe. The apparent order parameter “S”, and the isotropic hyperfine splitting constant “aN” increase with increasing salinity in Na2SO4, CaCl2, and NaCl systems. It is considered that the surfactant molecules are tightly packed in these systems and this tendency is highly related to the stability of gel-emulsions. The salt dehydrates the hydrophilic moiety of surfactant and hence the lateral interactions of surfactant molecular layer at the water-oil interface increases.

Visualization of 3D microstructure of bicontinuous microemulsions by combined SANS experiments and simulations

SANS studies were made on a three-component microemulsion system, with equal volume fractions of water and oil, in the one-phase region near the three-phase body, at the hydrophile—lipophile balance temperature, as a function of surfactant volume fraction φs. A prominent peak was found in the scattering intensity distribution, the position of which (Qmax) scaled linearly with φs. This scaling relation can be derived from a model of bicontinuous microemulsions proposed by Teubner and Strey (J. Chem. Phys., 87 (1987) 3195). It can be shown that the generic microstructure of these microemulsions is bicontinuous, characterized by two length scales d and ξ, where d is the average inter-domain distance between two water or oil domains and d/ξ the disorder parameter measuring polydispersity of the domain sizes. Based on this idea, we propose a simulation scheme, which is an extension of an idea of Berk (Phys. Rev. Lett., 58 (1987) 2718-2721; Phys. Rev. A, 44 (1991) 5069-5079), which allows us to generate both the 3D microstructure and the associated Debye correlation function, which can be Fourier transformed to obtain the theoretical scattering intensity distribution function. The main input to this simulation is a spectral function which is an inverse of a sixth order polynomial, containing three length scales. 3D micro-structures are then generated which are fully consistent with the scattering data. Physical meaning of the three length scales so obtained is discussed and compared with the two length scales d and ξ obtained from fitting the Teubner—Strey model to the same data.

The effect of salt concentration, temperature, and additives on the solvent property of aerosol OT solution

The effects of salt concentration, temperature, and additives on the phase behavior and HLB temperature of a brine/Aerosol OT/C10H22 system have been studied. The most important factor which affects the solvent property of a surfactant solution is its hydrophile-lipophile balance (HLB) in solution. Information obtained may be useful to design organized surfactant solutions as biomimetic solvents.