Microemulsion to Liquid-Crystal Transition in Two Anionic Surfactant Systems

Abstract

The phase behavior of two anionic surfactant systems, one containing a commercial alpha olefin sulfonate (AOS) and the other containing pure sodium dodecyl sulfate (SDS), was determined in the region where a transition from microemulsion to liquid-crystalline phases occurred with decreasing alcohol content and temperature. A general and rather complex pattern of phase behavior was seen that included a four-phase coexistence region of brine, microemulsion, lamellar liquid crystal, and oil, and two three-phase regions containing both microemulsion and liquid crystal. In much of the four-phase region, complete separation of the phases did not occur even after equilibration for I year or more at constant temperature. Instead, oil and brine were observed to coexist with stable birefringent dispersions that (for some compositions at least) apparently contained three phases: microemulsion, liquid crystal, and oil. Solubilization of brine was uniformly low in the phases making up the dispersions. The dispersions in the SDS system exhibited non-Newtonian behavior with apparent viscosities in the range of 50 to 100 mPa·s [50 to 100 cp] at a shear rate of 10 seconds -I. Microemulsion viscosities in the same system were about an order of magnitude lower. No plugging or other adverse behavior was seen when such dispersions flowed at a velocity of 10 -5 m/s [3 ft/D] through a model porous medium having pore sizes comparable with those in reservoirs. In preliminary experiments, selected dispersions appeared to be capable of displacing oil from the same model porous medium.

Characteristics of spontaneously formed nanoemulsions in octane/AOT/brine systems

“…A diagram presented by the latter group shows that the lamellar phase exists very close to the balanced condition at 0.3% NaCl but does not make clear whether a microemulsion is present. Perhaps the situation is similar to that reported by Hackett and Miller for other anionic surfactant systems where both phases can coexist with excess oil and brine for some conditions near the balanced state [48].…”

Spontaneous Emulsification of Oils Containing Hydrocarbon, Nonionic Surfactant, and Oleyl Alcohol

“…It has an unconventional form. The L 1 /ME/L 2 region does not terminate as surfactant concentration is increased at a junction with a single-phase microemulsion region, the behavior found in most systems (12) including the present one with n-octanol replacing oleyl alcohol (7), nor is it like the systems with rather rigid surfactant/ alcohol films where a four-phase L 1 /L ␣ /ME/L 2 region extends to low surfactant concentrations (13,14). Instead the L 1 /ME/L 2 region apparently terminates in a small four-phase region as indicated by a question mark in Fig.…”

Favorable Attributes of Alkaline-Surfactant-Polymer Flooding

“…Coexistence of a lamellar phase and a microemulsion has previously been observed at relatively low surfactant concentrations when alcohol concentration or temperature in certain microemulsions containing anionic surfactant fell below values needed to obtain the usual Winsor phase behavior with no liquid crystal (Hackett and Miller 1988). The Winsor sequence can be obtained in alkaline systems with N67 and MY4 by adding alcohol (Zhang 2006), but interfacial tensions are expected to rise with increasing alcohol content.…”