Lamellar to hexagonal columnar liquid crystalline phase transition in a catanionic surfactant mixture: dodecylammonium chloride–sodium bis(2-ethylhexyl) sulfosuccinate

Abstract

Phase transitions from a dispersed lamellar to hexagonal liquid crystalline phase have been investigated in a catanionic surfactant mixture formed by mixing a single tailed cationic surfactant, dodecylammonium chloride, with a double tailed anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate. Depending on the bulk composition and total surfactant concentration, mixed micelles, vesicles, lamellar and hexagonal columnar liquid crystalline phases have been identified. Differences in the geometry of the two hydrophobic chains stabilize vesicles of different shapes (spherical, tubular and pearled) relative to the liquid crystalline phase even in stoichiometric mixtures. At higher surfactant concentrations the phase transition from a dispersed lamellar to hexagonal columnar liquid crystalline phase proceeds continuously, with both phases coexisting over a range of concentrations. The transition proceeds through processes of vesicle aggregation, reorganization into multilayer sheets rolled-up into tubules, and formation of a hexagonal columnar liquid crystalline phase.

Recent Advances in Catanionic Mixtures

“…Catanionic vesicles usually have high degree of polydispersity, and their stability can be tailored by the choice of surfactant molecular structure, that is branched surfactants, and/ or those containing a bulky group in alkyl tail usually form more stable vesicles [6]. Likewise, in asymmetric surfactant mixtures, in terms of different alkyl chain numbers or length as well as different chain morphology, the vesicle phase is often considerably enlarged and found in a broad concentration range [14][15][16]. The size, surface charge density and permeability of catanionic vesicles can be tailored by varying temperature, concentration and molar ratio, as well as chain length of surfactants [17].…”

“…In the majority of catanionic mixtures at equimolar concentrations precipitate, a new catanionic surfactant, which very often possesses lamellar structure, forms [2,18]. It can form as only phase or in coexistence with (1) coacervates (small droplets in solution rich with surfactants) [6,24] as well as (2) micelles or (3) lamellar phase, usually in asymmetric mixtures [14,16,[22][23][24][25][26][27][28]. Formed precipitate can be redissolved by increasing concentration of one of the surfactants, leading to formation of micelles or vesicles.…”

“…Increased asymmetry in hydrophobic parts of surfactant molecules (different tail length or number, branched tails, rigid ring-based structures, etc.) weakens hydrophobic attractions among alkyl chains and prevents efficient packing into a crystalline lattice [14][15][16]29]. As a result, precipitation does not occur and instead large micelles, vesicles or liquid crystalline phases can be formed.…”

Investigating the effect of a simplified perfume accord and dilution on the formation of mixed-surfactant microemulsions

“…Surfactants are broadly shown to self-assemble into (a) discrete entities such as spheres, prolate ellipsoids, cylinders [11][12][13] or (b) continuous geometries wherein they are connected through macroscopic distances into hexagonal (1D), 14,15 lamellar (2D) [16][17][18] or bicontinuous/sponge phase (3D). [19][20][21] These three dimensional structures, also referred to as liquid crystalline structures, provide high viscosity and uidity to surfactants.…”

The DODAB–AOT–water system: vesicle formation and interactions with salts or synthetic polyelectrolytes

“…In general, the phase transitions and the overall phase behavior observed in this ternary system nd interesting analogy with the recent ndings on the chemically related DDAB/AOT one. 35,36 Drug delivery from catanionic vesicles relies on the electrostatic nature of binding by charged bio-macromolecules (proteins or nucleic acids). Fluorescence data, therefore, support the hypothesis of strong electrostatic contributions to binding onto vesicles.…”