Microemulsion formation and detergency with oily soils: I. Phase behavior and interfacial tension

Abstract

The ultimate objective of the project was to investigate the relationship between microemulsion phase behavior and detergency for oily soils. In this study, surfactant phase behavior was evaluated for hexadecane and motor oil as model oily soils. Producing microemulsions with these oils is particularly challenging because of their large hydrophobic character. To produce the desired phase behavior we included three surfactants with a wide range of hydrophilic/lipophilic character: alkyl diphenyl oxide disulfonate (highly hydrophilic), dioctyl sodium sulfosuccinate (intermediate character), and sorbitan monooleate (highly hydrophobic). This mixed surfactant was able to bridge the hydrophilic/lipophilic gap between the water and the oil phases, producing microemulsions with substantial solubilization and ultralow interfacial tension. The effects of surfactant composition, temperature, and salinity on system performance were investigated. The transition of microemulsion phases could be observed for both systems with hexadecane and motor oil. In addition, the use of surfactant mixtures containing both anionic and nonionic surfactants leads to systems that are robust with respect to temperature compared to single-surfactant systems. Under conditions corresponding to "supersolubilization," the solubilization parameters and oil/microemulsion interfacial tensions are not substantially worse than at optimal condition for a middle-phase system, so a middle-phase microemulsion is not necessary to attain quite low interfacial tensions. A potential drawback of the formulations developed here is the fairly high salinity (e.g., 5 wt% NaCl) needed to attain optimal middle-phase systems. The correlation between interfacial tension and solubilization follows the trend predicted by the Chun-Huh equation.

Enhanced triolein removal using microemulsions formulated with mixed surfactants

“…The experimental results showed that all of the values of IFT between the excess oil and excess water fall in the same range of 10 -2 to 10 -1 mN/m. The IFT values obtained from the present study agree well with literature values (6,11), which show that a system with triolein generally has a higher IFT than those with other hydrocarbon oils (10 -4 to 10 -2 mN/m) due to the bulky molecular structure of triolein.…”

“…Phase studies were carried out by first adding equal volumes of a surfactant solution and triolein into a flat-bottom screw-cap tube. The details of the phase behavior experiment were described in previous work (11). Both dynamic and equilibrium IFT of all prepared microemulsion systems were measured by a spinning drop tensiometer (model 500, University of Texas, Austin, TX).…”

“…Previous work on phase behavior of mixed surfactants with motor oil and hexadecane (11) showed that a mixture of a moderate-HLB surfactant with two cosurfactants, one of them very highly hydrophobic and the other very highly hydrophilic, was able to generate microemulsions with the two highly hydrophobic oils. This phenomenon occurs because the behavior of these two cosurfactants at the interface is analogous to lipophilic and hydrophilic linkers.…”

Laundry Detergency of Solid Non-Particulate Soil Using Microemulsion-Based Formulation

“…The aqueous surfactant solution and oil were added at a 1:1 v/v ratio to a series of 15-ml flat-bottomed screw-capped tubes 1,19,20,24 . Extended surfactant mixture systems were formulated at a high surfactant concentration of 4 wt with different concentrations of SMDNS from 0-1 and different NaCl concentrations in order to find a minimum hydrophilic linker and salinity for formation of a Winsor Type III microemulsion.…”

“…The mixture was packed into a sample holder and pressed to form a disk. The spectra were recorded over a wave number range of 4000-400 cm 1 with 64 scans at a resolution of 4 cm 1 .…”