Some observations on phase diagrams and structure in binary and ternary systems of sodium and calcium dodecyl(monooxyethylene) sulfate

Abstract

The phase equilibria of sodium (SDE 1S) and calcium (CDE 1S) dodecylmonooxyethylene sulfate in two- and three-component systems are studied by water deuteron NMR and polarizing microscopy methods. In the binary systems with water both SDE 1S and CDE 1S give micellar solutions, followed by the normal hexagonal liquid crystalline phases at 293 K. At high temperatures and with low water content, the lamellar liquid crystalline phases are also formed. The micellar aggregates with Ca 2+ as counterion start to grow at very low concentration whereas with Na + counterion, the micellar growth is observed only at very high surfactant concentration. The micellar solution and hexagonal liquid crystalline phases solubilize very small amounts of decanol which also increases the stability of the liquid crystalline phases toward the water corner. In the ternary system at 293 K, the coexistence of two lamellar liquid crystalline phases, one at high water content and the other at low water content, is detected with Ca 2+ as counterion whereas with Na + ion, there exists only one lamellar liquid crystalline phase with an extensive stability range. The lyotropic nematic liquid crystalline phases are found to form in the ternary systems with high water and very low decanol contents, and the structure of the phases are of lamellar-nematic type with Na + and hexagonal-nematic type with Ca 2+ as counterion. The calcium system also yields reverse hexagonal liquid crystalline phase with high both surfactant and decanol contents. The micellar growth and the coexistence of two lamellar liquid crystalline phases are explained qualitatively by recent theoretical models of attractive double-layer forces and image-charge interactions.