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AN INVESTIGATION OF THE MIDDLE PHASE MICROEMULSION TO LIQUID CRYSTAL TRANSITION IN ANIONIC SURFACTANT SYSTEMS AT LOW ALCOHOL CONTENT

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Title: AN INVESTIGATION OF THE MIDDLE PHASE MICROEMULSION TO LIQUID CRYSTAL TRANSITION IN ANIONIC SURFACTANT SYSTEMS AT LOW ALCOHOL CONTENT
Author: HACKETT, JAMES LAWRENCE, III
Abstract: Equilibrium phase behavior is reported for two anionic surfactant, alcohol, sodium chloride, water, n-decane systems, in the region where a transition occurred from microemulsion to liquid crystalline phases with decreasing alcohol content and decreasing temperature. One surfactant/co-surfactant pair studied was a commercial a -olefin sulfonate and n-butanol. The other was pure sodium dodecyl sulfate (SDS) and n-hexanol. A general, complex pattern of phase behavior was seen which 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. Compositional analysis of selected formulations in the four-phase region of the SDS system showed the liquid crystals to be oil-rich, making them different from lamellar phases in aqueous surfactant systems that contain over 90% water. In much of the four-phase region, complete separation of the phases did not occur even after yearlong equilibration at constant temperature. Instead, oil and brine were found to coexist with stable birefringent dispersions which, at least at some compositions, apparently contained three phases: microemulsion, liquid crystal, and oil. The dispersions in the SDS system exhibited non-Newtonian behavior with apparent viscosities ranging from 50 to 100 mPa s at a shear rate of 10 sec$\sp{-1}$. Microemulsion viscosities in the same system were an order of magnitude lower. Preliminary experiments suggest these dispersions are capable of displacing oil from a model porous medium when flowed at typical reservoir rates. They are thus of potential interest for enhanced oil recovery. Other investigations concerned the phase behavior of an ethoxylated, propoxylated sulfate system and two Zwitterionic surfactants in brine. The former study revealed a pattern of phase behavior similar to that reported for anionic surfactants with increasing salinity. However, with respect to temperature, these species behaved like nonionic surfactants. The Zwitterionic ammoniopropane sulfonates are unusual in that they display enhanced solubility in brine over that in pure water. As a result, a pattern of phase behavior reversed from that found in most anionic systems was observed with increasing salinity. A tentative explanation was given in terms of changes in surfactant molecular configuration with salinity, as suggested by others.
Citation: HACKETT, JAMES LAWRENCE, III. (1987) "AN INVESTIGATION OF THE MIDDLE PHASE MICROEMULSION TO LIQUID CRYSTAL TRANSITION IN ANIONIC SURFACTANT SYSTEMS AT LOW ALCOHOL CONTENT." Doctoral Thesis, Rice University. http://hdl.handle.net/1911/16062.
URI: http://hdl.handle.net/1911/16062
Date: 1987

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