The Lyotropic Mesophases in Dilute Surfactant Mixtures of Tetradecyldimethylaminoxide, Tetradecyltrimethylammonium Bromide, and Hexanol: The Influence of Ionic Charge on the Mesophases

Abstract

The influence of ionic charges on the mesophases in the ternary phase diagram of tetradecyldimethylaminoxide (C 14DMAO), hexanol, and water was studied. The charges were introduced by replacing C 14DMAO by the cationic surfactant tetradecyltrimethylammonium bromide (C 14TMAB). The phase diagram becomes much simpler by this substitution. The L 1- , L 3-, and L 3-phases which had previously been observed for the uncharged system are very sensitive to the charges and disappear completely with increased mole fraction of C 14TMAB ( Xc > 0.2). Furthermore, the L α1 - and the L αh-phases merge into a single L α-phase which has properties similar to those of the L α1-phase in the uncharged system. The most prominent feature of the charged L α-phase is its theological yield stress value. With increasing Xc the phase boundaries of the L 1- and the L α-phase are shifted to a higher mole fraction of alcohol ( Xa). The two phase regions ( L 1 + L α) widen with increasing X c. Samples in this two phase region separate easily into two phases. The properties of the different phases were determined and characterized by conductivity and theological measurement and by polarization microscopy. FF-TEM micrographs show that the charged L α-phase consists over the whole existence region of single and multilamellar vesicles. The vesicles at the lower phase boundary (low Xa-values) seem to have defects which disappear with increasing Xa-values. Finally, it is shown that with the addition of excess salt the phase diagram with the charged surfactant behaves again in the same way as the uncharged system.