Enhanced triolein removal using microemulsions formulated with mixed surfactants

In previous work, a microemulsion-based formulation approach yielded excellent laundry detergency with hydrophobic oily soils hexadecane and motor oil. In this work, the same approach is used in detergency of triolein, which is a model triglyceride, some of the most difficult oils to be removed from fabric. The linker concept was applied in formulation of the microemulsion system. Three different surfactants were used: (i) dihexyl sulfosuccinate, an ionic surfactant with a moderate hydrophile-lipophile balance (HLB); (ii) secondary alcohol ethoxylate, a lipophilic nonionic surfactant with a very low HLB; and (iii) alkyl diphenyl oxide disulfonate (ADPODS), a hydrophilic anionic surfactant with a very high HLB. The phase behavior and interfacial tension (IFT) of the surfactant systems were determined with different concentrations of ADPODS. The results indicate that as the HLB of the system increases, a higher salinity is required to shift the phase transition from Winsor Type I to Type III to Type II. The three formulations at different salinities were used in detergency experiments to remove triolein from polyester/cotton sample fabric. The results showed that there were two peaks of maximum detergency in the range of salinity from 0.1% to 10% NaCl. The higher the hydrophilicity of the system, the higher the salinity required for maximum detergency. The results of the dynamic IFT and the detergency performance from two rinsing methods lead to the hypothesis that one of these maxima in detergency results from a spreading or wetting effect. The other maximum in detergency is believed to be related to ultralow IFT associated with oil/water middle-phase microemulsion formation. Triolein removal exceeding 80% was attained, validating the microemulsion approach to detergency.     

Microemulsion formation and detergency with oily soils: II. Detergency formulation and performance

In part I of this series (J. Surfact. Deterg. 6, 191–203, 2003), the mixed surfactant system of sodium dioctyl sulfosuccinate (AOT), alkyl diphenyl oxide disulfonate (ADPODS) and sorbitan monooleate (Span 80) was shown to form Winsor type I and type III microemulsions with hexadecane and motor oil. In addition, high solubilization and low interfacial tension were obtained between the oils and surfactant solutions both in the supersolubilization region (Winsor type I system close to type III system) and at optimal conditions in a type III system. In the present study, this mixed surfactant system was applied to remove oily soil from fabric (a polyester/cotton blend), and detergency results were correlated to phase behavior. Dynamic interfacial tensions were also measured between the oils and washing solutions. In the supersolubilization and in the middle-phase regions (type III), much better detergency performance was found for both hexadecane and motor oil removal than that with a commercial liquid detergent product. In addition, the detergency performance of our system at low temperature (25°C) was close to that obtained at high temperature (55°C), consistent with the temperature robustness of the microemulsion phase behavior of this system.     

New Interfacial Rheology Characteristics Measured Using a Spinning Drop Rheometer at the Optimum Formulation. Part 2. Surfactant–Oil–Water Systems with a High Volume of Middle-Phase Microemulsion

This article is a continuation of our first study on dilational interfacial rheology properties at optimum formulation for surfactant-oil–water systems at low surfactant concentration just above the cμc. Here, we have investigated a high content of middle-phase microemulsion with an optimum WIII phase behavior for a system containing sodium dodecyl sulfate, n-pentanol, and kerosene. A new oscillating spinning drop interfacial rheometer was used to measure the interfacial properties. The very low dilational elasticity moduli and phase angle found at or near hydrophilic–lipophilic deviation (HLD) = 0 are related to the presence of the bicontinuous phase microemulsion and to the fast surfactant exchanges between the bulk and the interface, regardless of the phases involved in the measurement using the spinning drop apparatus, i.e., the two-phase excess oil and excess water (O-W) or the bicontinuous microemulsion and excess water (M-W). We show that at or near optimum formulation, the interfacial tension and the dilational modulus for the M-W case almost instantly reach equilibrium, because of the high surfactant content in the microemulsion and the fast exchanges between the bulk and the interface. In contrast, when both excess phases (O-W) are measured, the changes in these properties are slower, due to the scarce presence of surfactants in both phases. The possibility of having almost all the surfactants trapped in the middle-phase bicontinuous microemulsion could explain the emulsion instability in all the WIII range. This is behaving as if there were no surfactant available in the oil and water phases to stabilize the oil or water droplets thus formed.     

Alcohol-free diphenyl oxide disulfonate middle-phase microemulsion systems

Diphenyl oxide disulfonate (DPDS) surfactants were successfully used to formulate Winsor Type III middlephase microemulsion systems with tetrachloroethylene (PCE) and decane. To our knowledge this is the first time that monochain DPDS surfactant phenyloxide monohexadecyl disulfonate surfactant (C16MADS) and commercially available DOWFAX 8390 were found to form middle-phase microemulsion systems with oils. Hydrophobic dioctyl sodium sulfosuccinate (Aerosol OT) was also used as a cosurfactant to lower the systems' hydropholic-liphophilic balance. Two organic acids (hydrophobic octanoic acid and hydrophilic l-tartaric acid) were used in place of the alcohol to formulate middle-phase microemulsion. The middle-phase microemulsion systems dramatically increased organic solubility when compared to micellar DPDS surfactant systems. Winsor Type I systems near the Type I–III boundary produced “super” solubilization for hydrophobic oils. Findings from this study enable us to improve DPDS solubilization enhancement of hydrophobic compounds.     

Anionic and Cationic Surfactant Synergism: Minimizing Precipitation,Microemulsion Formation,and Enhanced Solubilization and Surface Modification

Anionic–cationic surfactant mixtures are known to exhibit synergistic effects (e.g., low critical micelle concentration, ultralow interfacial tension, middle phase microemulsion formulation, and increased solubilization and adsolubilization). However, the anionic–cationic surfactant mixtures are also prone to form other unique phases such as precipitates, gels, and coacervates in place of middle-phase microemulsions. Research summarized in this article demonstrates that asymmetric anionic–cationic surfactant mixtures have been shown to promote middle-phase microemulsions instead of these other phases, albeit with a slight decrease in synergism when using these asymmetric mixtures. The use of anionic–cationic surfactant mixtures also is shown to enhance or decrease surfactant adsorption depending on anionic–cationic surfactant ratios. Middle-phase microemulsion formation is demonstrated using anionic-rich or cationic-rich alcohol-free microemulsions by anionic–cationic ratio scans while also reducing or eliminating electrolyte requirement. Solubilization and adsolubilization are shown to increase for mixed anionic–cationic surfactant systems, especially for hydrophobic solutes. Thus, by exploiting these synergisms while avoiding phase separation, properly designed anionic–cationic surfactant mixtures can be advantageous for a wide range of applications.     

Formulation of ultralow interfacial tension systems using extended surfactants

Inspired by the concept of lipophilic and hydrophilic linkers, extended surfactants have been proposed as highly desirable candidates for the formulation of microemulsions with high solubilization capacity and ultralow interfacial tension (IFT), especially for triglyceride oils. The defining characteristic of an extended surfactant is the presence of one or more intermediate-polarity groups between the hydrophilic head and the hydrophobic tail. Currently only limited information exists on extended surfactants; such knowledge is especially relevant for cleaning and separation applications where the cost of the surfactant and environmental regulations prohibit the use of concentrated surfactant solutions. In this work, we examine surfactant formulations for a wide range of oils using dilute solutions of the extended surfactant classes sodium alkyl polypropyleneoxide sulfate (R-(PO) _x −SO₄Na), and sodium alkyl polypropyleneoxide-polyethyleneoxide sulfate (R-(PO) _y -(EO) _z −SO₄Na). The IFT of these systems was measured as a function of electrolyte and surfactant concentration for polar and nonpolar oils. The results show that these extended surfactant systems have low critical micelle concentrations (CMC) and critical microemulsion concentrations (CμC) compared with other surfactants. We also found that the unique structure of these extended surfactants allows them to achieve ultralow IFT with a wide range of oils, including highly hydrophobic oils (e.g., hexadecane), triolein, and vegetable oils, using only ppm levels of these extended surfactants. It was also found that the introduction of additional PO and EO groups in the extended surfactant yielded lower IFT and lower optimum salinity, both of which are desirable in most formulations. Based on the optimum formulation conditions, it was found that the triolein sample used in these experiments behaved as a very polar oil, and all other vegetable oils displayed very hydrophobic behavior. This unexpected triolein behavior is suspected to be due to uncharacterized impurities in the triolein sample, and will be further evaluated in future research.     

INTERFACIAL COMPOSITION OF MICROEMULSIONS: MODIFIED SCHULMAN-BOWCOTT MODEL

The interfacial composition of oil-external microemulsions formed with sodium stearate, pentanol, brine and various oils (octane, dodecane and hexadecane) was determined in terms of moles of alcohol per mole of surfactant present at the interface (niⁱ_a/n_3,) using a modified three compartment Schulman-Bowcott model. The modified model takes into account the solubility of pentanol in aqueous and hydrocarbon phases. For a constant brine/surfactant ratio, it was found that the value of (niⁱ_a/n_3,) was highest for dodecane containing microemulsion which corresponded to the maximum solubilization of brine in this microemulsion at optimal salinity. This behavior is explained on the basis of chain length compatibility in microemulsions. The optimal salinity for solubilization increased with the chainlength of oil.     

不同因素对CTAB/TX-100微乳液相图的影响

用ε-β"鱼状"相图法研究了阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)与非离子表面活性剂辛基苯酚聚氧乙烯(10)醚(TX-100)以不同摩尔比复配形成的CTAB/TX-100/醇/油/NaCl水溶液微乳液体系的相行为和增溶性能.结果表明,随着醇浓度的增加,体系由水包油型(O/W)(winsor Ⅰ or (2-)...     

Formulating middle-phase microemulsions using mixed anionic and cationic surfactant systems

Although mixtures of anionic and cationic surfactants can show great synergism, their potential to precipitate and form liquid crystals has limited their use. Previous studies have shown that alcohol addition can prevent liquid crystal formation, thereby allowing formation of middle-phase microemulsions with mixed anionic-cationic systems. This research investigates the role of surfactant selection in designing alcohol-free anionic-cationic microemulsions. Microemulsion phase behavior was studied for three anionic-cationic surfactant systems and three oils of widely varying hydrophobicity [trichloroethylene (TCE), hexane, and n-hexadecane]. Consistent with our hypothesis, using a branched surfactant and surfactants with varying tail length allowed us to form alcohol-free middle-phase microemulsion using mixed anionic-cationic systems (i.e., liquid crystals did not form). The anionic to cationic molar ratio required to form middle-phase microemulsions approached 1∶1 for univalent surfactants as oil hydrophobicity increased (i.e., TCE to hexane to n-hexadecane); even for these equimolar systems, liquid crystal formation was avoided. To test the use of these anionic-cationic surfactant mixtures in surfactant-enhanced subsurface remediation, we performed soil column studies: Greater than 95% of the oil was extracted in 2.5 pore volumes using an anionic-rich surfactant system. By contrast, cationic-rich systems performed very poorly (<1% oil removal), reflecting significant losses of the cationic-rich surfactant system in the porous media. The results thus suggest that, when properly designed, anionic-rich mixtures of anionic and cationic surfactants can be efficient for environmental remediation. By corollary, other industrial applications and consumer products should also find these mixtures advantageous.     

Fourier transform infrared spectroscopy in surfactant science: A personal view

The overall goal of this review paper on Fourier transform infrared spectroscopy (FT-IR) is to provide non-specialists and spectroscopists alike a motivational introduction to how this technique may be used to obtain unique structural information on a wide range of surfactant-based systems. Two main topics are addressed—The structures of surfactant aggregates in solution and the interactions of surfactants in solution with solid surfaces. Infrared spectra can yield insights into the interactions of surfactants in mixed micelles as well as in microemulsions. The structures of adsorbed surfactant layers and their kinetics of formation may be elucidated from FT-IR spectra obtained using attenuated total reflectance sampling techniques. Insights into the detergency process of solid oily soils may also be obtained from the spectra of phases formed at the soil-surfactant solution interface. Future work in applying FT-IR to the development of the hydrophilic–lipophilic difference + net average curvature (HLD-NAC) framework is proposed. Spectral interpretation principles examined in many examples, particularly regarding surfactant hydration and the loci of oil solubilization, could be used in the further development of HLD-NAC through application to some microemulsion systems that have recently been reported.     

The HLD-NAC Model for Extended Surfactant Microemulsions

It has been confirmed that the structure of the alkyl group of an extended surfactant plays an important role in defining its interfacial properties. Alkyl groups containing a higher degree of ??-branching (C2-branching) produce microemulsions with a larger characteristic length (??, the extent of solubilization in middle phases). This effect is explained on the basis that ??-branching increases the hydrophobicity of the surfactant and decreases the optimal salinity of the microemulsion. Higher salinities produce a dehydration of the surfactant groups that lead to shorter extent of the interactions with the oil and the water. Larger characteristic lengths are desirable if the objective of the formulation is obtaining greater solubilization of oil and water, and lower interfacial tensions. Large characteristic lengths are, in most cases, associated with high interfacial rigidities, which are undesirable if rapid coalescence is required. However, mixtures of branched and linear extended surfactants produce large characteristic lengths and lower interfacial rigidities. The HLD-NAC model is able to reflect the experimental trends in solubilization of oil and water. The differences between the predictions of the model for the solubilization of oil and water in Type I and II formulations, respectively, highlight the complexities in the conformation of extended surfactants, particularly their PO groups, at oil?Cwater interfaces and the need for advanced scattering techniques to evaluate these conformations.     

Carboxylate surfactant systems exhibiting phase behavior suitable for enhanced oil recovery

A large variety of aliphatic and aromatic carboxylate surfactants with alcohols as cosurfactants displayed phase behavior with n-decane that indicated they could be useful in enhanced oil recovery. Three-phase systems with large volume fraction middle-phase microemulsions were observed with sodium isostearate and sodium oleate. The interfacial tension between top and bottom phases was at a minimum (∼0.001 dyne/cm) at the optimal salinity where the uptake of oil and water in the middle phase was equal. The phase behavior of carboxylates was affected by pH and added bases. In cases where a bicarbonate-carbonate buffer was used to control pH, the optimal salinity decreased as the pH decreased. Use of ethoxylated alcohols as cosurfactants increased optimal salinities markedly and caused formation of very large volume fraction middle phases. Neutralized tall oils and tall oil fatty acids with alcohols as cosurfactants gave 3-phase behavior with n-decane with large volume fraction middle-phase microemulsions.     

Linker-modified microemulsions for a variety of oils and surfactants

Previously, we reported on the use of hydrophilic and lipophilic linker molecules to enhance the solubilization capacity of chlorinated hydrocarbons using sodium dihexyl sulfosuccinate (SDHS). In this work we extend the use of linker molecules to a wider range of oils and surfactants. The data show that the linker effect works for all the systems studied and that linker-based systems are even more economical than surfactant-only systems for more hydrophobic oils. Using a more hydrophobic surfactant, such as sodium bis(2-ethyl)dihexyl sulfosuccinate (Aerosol-OT), requires a formulation enriched with a hydrophilic linker, whereas the formulation for the more hydrophilic SDHS requires the use of a more lipophilic linker. By considering the properties and appearance of the formulation before contacting with the oil, and by evaluation the coalescence dynamics, we found that hydrophilic linker-rich formulations were preferred. These formulations were tested as fabric pretreatments for removing motor oil and hexadecane from cotton, and as flushing solutions for glass bead columns contaminated with these oils. The cleaning performance of these linker-based systems was superior to common surfactant and pretreatment formulations in the detergency tests, achieving more than 80% removal of motor oil and hexadecane trapped in the packed-column flushing tests.     

Effect of Alkyl Sulfate on the Phase Behavior of Microemulsions Stabilized with Monoacylglycerols

In this study the effect of an anionic surfactant (sodium dodecyl sulfate SDS) and oils (hydrocarbons: C12–C16) on the formation and phase behavior of the systems of oil/monoacylglycerols (MAG):SDS/propylene glycol/water has been investigated. The effects of the surfactant mixture on the phase behavior and the concentration of water or oil in the systems were studied at three temperatures (50, 55, 60 °C). Electrical conductivity measurement, FT-IR spectroscopy and differential scanning calorimetry methods were applied to determine the structure and type of the microemulsions formed. The dimension of microemulsion droplets was characterized by dynamic light scattering. It has been stated that the concentration of SDS has a strong influence on the shape and extent of the microemulsion areas. Addition of an ionic surfactant to the mixture with MAG promotes an increase in the area of microemulsion formation in the phase diagrams, and these areas of the isotropic region change with the temperature. It was shown that the presence in the systems of a surfactant more hydrophilic than MAG caused an increase in water content in the microemulsions. It was found that, depending on temperature and concentration of the surfactant mixture, it was possible to obtain a W/O type microemulsion with a dispersed particles size distribution ranging from 20 to 50 nm and containing about 17–38% water in the system. Among different alkanes (from C12 to C16), hexadecane embedded microemulsions showed a maximum water solubilization capacity.     

The role of hydrophilic linkers

In microemulsion formulations, linker molecules are additives that can enhance the surfactant-oil interaction (lipophilic linkers) or the surfactant-water interaction (hydrophilic linkers). In this paper, the role of the hydrophilic linker is elucidated through solubilization studies, interfacial tension studies, and by studying the partitioning of the hydrophilic linker into an optimum middle phase. This research used alkyl naphthalene sulfonates as the hydrophilic linkers, sodium dihexyl sulfosuccinate as the surfactant, and trichloroethylene as the oil phase. The hydrophilic linkers were found to have interfacial properties between a hydrotrope and a cosurfactant. More specifically, the data show that a hydrophilic linker is an amphiphile that coadsorbs with the surfactant at the oil/water interface but that has negligible interaction with the oil phase. The role of the hydrophilic linker can thus be interpreted as opening “holes” in the interface. Based on the characteristics of alkyl naphthalene linkers, carboxylic molecules were evaluated as hydrophilic linkers. For trichloroethylene microemulsions, sodium octanoate was found to be an alternative hydrophilic linker to sodium mono- and dimethyl naphthalene sulfonates.     

Microemulsion phase behavior of anionic-cationic surfactant mixtures: Effect of tail branching

This research evaluated middle-phase microemulsion formation by varying the mole ratio of anionic and cationic surfactants in mixtures with four different oils (trichloroethylene, n-hexane, limonene, and n-hexadecane). Mixtures of a double-tailed anionic surfactant (sodium dihexyl sulfosuccinate, SDHS) and an unbalanced-tail (i.e., doubletailed with tails of different length) cationic surfactant (benzethonium chloride, BCl) were able to form microemulsions without alcohol addition. The amount of NaCl required to form the middle-phase microemulsion decreased dramatically as an equimolar anionic-cationic surfactant mixture was approached. Although the mixture of anionic and cationic surfactants demonstrated a higher critical microemulsion concentration (cμc) compared to the anionic surfactant alone, the Winsor Type IV single-phase microemulsion started at lower surfactant concentrations for the anionic-cationic mixture than for the anionic surfactant alone. Under optimum middlephase microemulsion conditions, mixed anionic-cationic surfactant systems solubilized more oil than the anionic surfactant alone. Pretreatment detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil form fabrics. It was found that anionic-rich mixed surfactant formulations yielded the largest oil removal, followed by cationic-rich systems.     

Environmentally Friendly Vegetable Oil Microemulsions Using Extended Surfactants and Linkers

Microemulsion formation of triglyceride oils at ambient conditions (temperature and pressure) and without the addition of co-oil and/or alcohols is challenging at best. Undesirable phases, such as macroemulsions, liquid crystals and sponge phases, are often encountered when formulating triglyceride microemulsions. The purpose of this study is to investigate the use of extended surfactants, lipophilic linkers, and hydrophilic linkers in enhancing triglyceride solubilization and interfacial tension reduction. We have studied two classes of extended surfactants, linear alkyl polypropoxylated sulfate (LAPS) surfactants and linear alkyl polypropoxylated ethoxylated sulfate (LAPES) surfactants. Linkers evaluated were oleyl alcohol (lipophilic linker), sodium mono and dimethyl naphthalene sulfonate (SMDNS), and polyglucoside (hydrophilic linkers). Oils studied include olive, peanut, soybean, canola and sunflower oils. The effect of electrolyte concentration on microemulsion phase behavior was studied. The microemulsion “fish” diagram was obtained by plotting the total surfactant and linker concentrations versus the electrolyte concentration. We were able to form Winsor Type I, II, III and IV microemulsions at ambient conditions and without co-oil or short and medium chain length alcohol addition. Winsor Type III and IV triglyceride microemulsions are particularly useful in numerous applications such as cosmetics, vegetable oil extraction and soil remediation.

Phase Behavior of Non-Ionic Surfactant-Medium Chain Triglyceride-Water Microemulsion Systems

Microemulsion systems have garnered tremendous interest in the pharmaceutical sector for a variety of drug delivery applications. Non-ionic surfactants are often the preferred surfactant class given their uncharged nature, enhanced oral safety profile, and generally regarded as safe status as compared to other surfactant classes (Myers, Surfactant science and technology, 2005, p. 29), (Malmsten, Handbook of microemulsion science and technology, 1999, p. 755), (Grove & Mullertz, Chapter 5-liquid self-microemulsifying drug delivery systems, 2007), (Liu et al., Water-insoluble drug formulation, 2008), (Hauss, Advanced Drug Delivery Reviews, 2007, 59, pp. 667–676), (Balazs, Solubility, delivery and ADME problems of drugs and drug-candidates, 2011, p. 68). In this work, the phase behavior and microemulsion formation potential of four commonly used non-ionic surfactants, PEG-40 hydrogenated castor oil, Poloxamer 188, Polysorbate 80, and d -α-tocopherol polyethylene glycol succinate were studied via ternary phase diagram (TPD) mapping using a medium chain triglyceride, Miglyol 812. Results indicated notable differences in phase behavior despite similarities in hydrophilic–lipophilic balance value (13–15). All surfactants produced Winsor Type I, oil-in-water microemulsions at water concentrations above 40% wt/wt. Winsor Type II water-in-oil microemulsions were difficult to obtain even at high oil concentrations of ≥70% wt/wt. Winsor III microemulsions, though rare, were generally obtained in the middle regions of the TPD between 10% and 30% wt/wt water while Winsor IV microemulsions dominated at high surfactant concentrations of ≥45% wt/wt. Opaque emulsion areas were particularly notable in wax state surfactants. Polysorbate 80 and PEG-40 hydrogenated castor oil demonstrated a high degree of synergism as well as the largest oil-in-water (o/w) and water-in-oil (w/o) microemulsion formation potential rendering them suitable for a number of enteral and parenteral applications.     

New Interfacial Rheology Characteristics Measured using a Spinning‐Drop Rheometer at the Optimum Formulation of a Simple Surfactant–Oil–Water System

A new spinning‐drop tensiometer with an oscillating rotation velocity was used to measure the interfacial rheological properties of systems with very low interfacial tensions in the zone close to the so‐called optimum formulation of surfactant–oil–water systems. 2 simple formulation scans were selected: One with an extended anionic surfactant using a salinity variation in the water phase, and another with a mixture of 2 nonionic surfactants in a scan produced by changing their proportion. With both systems it was corroborated that at optimum formulation (i.e., at hydrophilic–lipophilic deviation (HLD) = 0), both the interfacial tension and the emulsion stability exhibit a deep minimum. A clear relationship was also found between the phase behavior and the interfacial rheological properties (dilational elasticity and viscosity). For the very first time and in both kinds of scans (salinity or average ethylene oxide number), it was found that the interfacial elastic modulus E and the interfacial viscosity, as well as the phase angle also exhibit a minimum at optimum formulation. These groundbreaking findings could be applied to emulsion instability at optimum formulation and to its applications in emulsion breaking.     

Gemini表面活性剂/醇/正辛烷/盐水体系微乳液的研究

以壬基酚为原料在催化剂存在下与二溴烷烃作用生成双醚,然后磺化,合成了一类Gemini阴离子表面活性剂,用悬滴法测定了其油水界面张力,结果表明,Gemini表面活性剂可使油水界面张力降低到 10-3mN/m。研究了Gemini表面活性剂 /醇 /正辛烷 /盐水体系的微乳液相行为,通过拟三元相图的方法确定了助表面活性剂醇的种类,实验结果表明,链长的比链短的醇具有更好的助活作用。通过正交实验方法得到了形成中相微乳液的最佳组成:w(GeminiD) =0 1%;w(n C6H13OH) =4 0%;w(NaCl) =1 5%。