Aqueous phase behaviour of choline carboxylate surfactants—exceptional variety and extent of cubic phases

Abstract

Choline carboxylate surfactants are powerful alternatives to the well-known classical alkali soaps, since they exhibit substantially increased water solubility while maintaining biocompatibility, in contrast to simple quaternary ammonium ions. In the present study, we report the aqueous binary phase diagrams and a detailed investigation of the lyotropic liquid crystalline phases formed by choline carboxylate surfactants (ChCm) with chain lengths ranging from m ¼ 12-18 and at surfactant concentrations of up to 95-98 wt%. The identification of the lyotropic mesophases and their sequence was achieved by the penetration scan technique. Structural details are elucidated by small-angle X-ray scattering (SAXS). The general sequence of mesophases with increasing soap concentration was found to be as follows: micellar (L 1 ), discontinuous cubic (I 1 ), hexagonal (H 1 ), bicontinuous cubic (V 1 ) and lamellar (L a ). The main difference to the phase behavior of alkali soaps or of other mono-anionic surfactants is the appearance and large extent of a discontinuous cubic phase with two or even more different symmetries. The obtained phase diagrams further highlight the extraordinarily high water solubility of ChCm soaps. Finally, structural parameters of ChCm salts such as the cross-sectional area at the polarnonpolar interface are compared to those of alkali soaps and discussed in the terms of specific counterion binding and packing constraints.

Effect of choline carboxylate ionic liquids on biological membranes

“…Compared to the long chain choline carboxylates (ChC m with m = 11–16) the IC 50 value of choline octadecanoate is in the same range for the HeLa and the SK-MEL-28 cells [49]. Also, the toxicity of choline oleate is in the range of choline octadecanoate.…”

Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal

“…For the sample containing 50 wt% water, only the hexagonal phase is observed, showing a characteristic hexagonal pattern: q 1 (100) : q 2 (110) : q 3 (200) : q 4 (210) = 1 : O3 : O4 : O 7 (Fig. 9,[11][12][13]16,38,39 The I 1 present in the C 16 mimAcr/water system could be properly indexed as a Pm3n lattice with up to 13 identified reflection peaks. The d spacing for the 50 wt% hexagonal phase has increased to 46.5 Å indicating a looser packing of the micellar cylinders.…”

“…4). The Pm3n space View Article Online group consists of two spherical and six disc-shaped micelles per unit as proposed by Charvolin and Sadoc 9,13,17,40,41 The unit cell parameter, a, for the I 1 phase is determined to be equal to 117 Å for the sample containing 65 wt% water. 9 At around 60-65 wt% water, the formation of a discontinuous cubic phase (I 1 ) is observed, as evidenced by the SAXS profiles in Fig.…”

“…[1][2][3][4][5] Lyotropic liquid crystalline phases are formed by the spontaneous self-assembly of amphiphilic molecules with the addition of a co-solvent, typically water, alcohol or glycerol. 9,[11][12][13][14] These architectures display exceptional properties such as bimodal pore size distribution (i.e. 9,[11][12][13][14] These architectures display exceptional properties such as bimodal pore size distribution (i.e.…”

Thermotropic Phase Behavior of Choline Soaps

“…m = 12À18 in which at least five different liquidÀcrystalline structures were shown to occur. 12 Thus, choline soaps are expected to display also thermotropic mesomorphism.…”