Solid and liquid crystalline phases in the sodium dodecyl sulphate + hexadecanoic acid + water system

Abstract

In this work an outline has been obtained of the ternary diagram for the sodium dodecyl sulphate + hexadecanoic acid + water system at 50°C using optical, n.m.r. and differential thermal methods.

Areas of lamellar and hexagonal mesophases have been defined and the minimum temperatures for the existence of these mesophases in the ternary system and also in the binary sodium dodecyl sulphate + water system have been determined.

These temperatures have been correlated with the minimum temperatures at which sodium dodecyl sulphate solution will interact with hexadecanoic acid crystals to form lamellar and hexagonal liquid crystalline phases.

The constant temperature of formation of the lamellar mesophase in ternary mixtures has been correlated with the existence of a solid compound of composition, 2SDS : C₁₆A : xH₂O, where x∼ 8. This has been confirmed by examining in detail specific areas of the phase diagram at lower temperatures, and by the use of broad line nuclear magnetic resonance spectroscopy.