Salt-free vesicle-phases and their template effect

Abstract

Researches on the construction, structure, and formation of vesicles formed from surfactants have attracted great attention from colloid and interface chemists. The vesicles formed from salt-free cationic-anionic surfactant systems are very different from those with excess salts, having many particular properties. In this paper, we introduce the properties of vesicles prepared from salt-free surfactant systems, according to our own results, especially the vesicles formed from surfactants with divalent metal ions as counterions in aqueous solutions and room temperature ionic liquids. Moreover, the primary results on template effect of the metal-ligand vesicles have also been summarized.salt-free surfactant system, vesicle, room temperature ionic liquids (RTILs), template effectThe surfactants and their mixture systems can form diverse aggregates in aqueous solutions such as micelles, vesicles, lamellar phases and cubic phases, due to their peculiar structure with both hydrophilic and hydrophobic structures [1][2][3] . Among these aggregates, the vesicle phase is of particular interest and has attracted a large number of investigations because of the potential of these equilibrium aggregates to serve as good biological model membranes, as containers for encapsulation and eventual release of drugs, flavors, and fragrances, and as microreactors for the formation of a range of inorganic nanoparticles [4][5][6] .Catanionic surfactant systems (cationic-anionic surfactant mixture systems) are a sort of important systems that were often used to obtain spontaneously formed vesicle phases. Among them, the systems with excess inorganic salts were investigated in early times [7][8][9][10][11] , in which the counterions of the surfactants form excess salts when the cationic surfactants and anionic surfactants mixed. Usually, the salts shield the surface ionic charges of the molecular membranes formed by the connection of the two kinds of surfactants and affect the electrostatic interactions between the membranes (monolayers or bilayers). As a result, the vesicles obtained by this method often have low yield values and precipitates are usually produced without vesicle formed when the two surfactants mixed at equal mole. On the contrary, there are no precipitates forming in salt-free surfactant systems and some novel aggregates can be obtained in the absence of the excess salts and the shield induced by the salts [12][13][14][15][16][17][18][19] . Hence, our group also performed some studies on salt-free systems, and got some interesting results.In this paper, some reported results, including our own results, such as the construction of vesicle phases and the properties of these vesicle phases, especially the vesicles formed by the divalent metal-ligand surfactant systems, are introduced and the further work that should be focused on is discussed.

Polymer–vesicle association

“…Another interesting case to analyse is that of salt-free catanionic surfactants, for which spontaneous vesiculation in zero salt concentration and without excess of ionic surfactant has also been reported to occur [46,[126][127][128][129][130][131][132][133][134][135]. These systems have the further advantage that the effect of electrostatic interactions can be studied in a controlled way by the addition of salt.…”