Interfacial Properties of Extended-Surfactant-Based Microemulsions and Related Macroemulsions

Extended surfactants containing an intermediate-polarity spacer, such as polypropylene oxide, in between the hydrophilic head and the hydrocarbon tail are known to result in superior solubilization and low interfacial tension, though they exhibit slow kinetics. The present work seeks to evaluate both equilibrium and kinetic aspects of extended-surfactant-based micro- and macroemulsions. The interfacial morphology of the extended surfactant membrane, i.e., characteristic length (ξ) and interfacial rigidity (E _r) at optimum middle-phase microemulsion conditions, was characterized using the net-average curvature model. The results showed that extended surfactants resulted in a relatively rigid interfacial membrane compared with conventional surfactants having similar hydrocarbon chain length. In addition, both ξ and E _r parameters increased with the length of the polypropylene oxide spacer. Increasing E _r values correlated to the slow coalescence rates of extended surfactant emulsified systems. Two alternative approaches (the addition of combined linkers and co-surfactant) are shown to overcome the slow kinetics of coalescence while maintaining desirable high solubilization and low interfacial tension.     

Linker-based bio-compatible microemulsions

In this work we have studied the formulation of biocompatible microemulsions using lecithin as the main surfactant and bio-compatible linker molecules (hexyl polyglucoside asthe hydrophilic linker and sorbitan monoleate as the lipophilic linker). These bio-compatible systems are discussed as potential substitutes for chlorinated solvents in dry-cleaning applications and as solvent delivery systems for pharmaceutical applications. Formulation parameters and conditions were evaluated using isopropyl myristate (IPM) as the model oil. It was found that the proposed linker-based formulations were able to form alcohol-free microemulsions while achieving higher solubilization capacity than similar systems reported in the literature. In addition, these lecithin/linker formulations were able to form microemulsions with a wide range of oils, from polar chlorinated hydrocarbons to hydrophobic oils such as squalene. These microemulsions were achieved under isotonic conditions (0.9% NaCl) by only varying the relative proportions of the linkers. The "solvency" power of these bio-compatible formulations was tested for the removal of hexadecane (used as model oil) from cotton fabrics and compared to the solvency power of a typical dry cleaning solvent tetrachloroethylene (PCE). While PCE and the linker-based lecithin formulation removed the same amount of hexadecane at low loading ratios (less than 1% oil volume fraction), at higher loading ratios the linker-based lecithin formulation retained its oil removal capacity while the efficiency of the PCE system declined rapidly. These initial results thus demonstrate the remarkable oil solubilization capacity of these bio-compatible linker-based lecithin formulations and illustrate their potential as environmentally friendly replacements for organic solvents.     

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.

Microemulsion-Based Vegetable Oil Detergency Using an Extended Surfactant

This work examined the use of a single extended surfactant in the microemulsion-based detergency of vegetable oils. The results showed that good canola oil detergency (>80%) was achieved at 25 °C using a single extended surfactant (C_14,15–8PO–SO₄Na) at concentrations as low as 125 ppm, i.e., significantly lower than the surfactant concentration range of 500–2,500 ppm reported in other microemulsion-based detergency work. It was found that the maximum detergency (95%) was achieved in the type II microemulsion region. These results demonstrate that the microemulsion-based extended surfactant formulation is a promising approach for vegetable oil detergency at low temperature.