Measurement of Forces between Spontaneous Vesicle-Forming Bilayers

Abstract

The forces between bilayers self-assembled onto mica from dilute aqueous solutions containing vesicles of mixed cationic surfactant cetyltrimethylammoniun tosylate (CTAT) and anionic surfactant sodium dodecylbgnzenesulfonate (SDBS) were measured using the surface forces apparatus. At large separations (D > 20 A) the forces can be described by the DLVO theory of repulsive electrostatic and attractive van der Waals forces; in dilute solution, the electrostatic repulsion is sufficient to make the net interaction ofthe mixed surfactant bilayers repulsive at all separations. The electrostatic force dominates any undulation or other long-range interactions and is sufficient to render the vesicles stable against aggregation in dilute solution. Although the net interactions between the mixed surfactant bilayers were monotonically repulsive, fusion of the bilayers could be induced at applied pressures orders of magnitude lower than for singlecomponent phospholipid or surfactant bilayers. At sufficiently high concentrations of added salt ('0.5 M), the electrostatic interactions were screened sufficiently that multilayers were trapped between the surfaces. The measured forces correlate well with the ternary phase diagram and thevesicle microstructures observed using freeze-fracture and cryo-electron microscopy.

Micellization and interfacial behavior of 16-E2-16 in presence of inorganic and organic salt counterions

“…The oft chosen cetyltrimethylammonium bromide/chloride (CTAB/CTAC) and sodium dodecylsulphate (SDS) have, respectively, been used as the representatives of cationic and anionic surfactants. Owing to their superior properties, due attention has been paid to gemini surfactants too but only with the m-s-m type (where, m is the carbon number in alkyl chain length and s is the carbon number in spacer chain length) bearing ammonium headgroups with long alkyl chains (m=12, 14,16) and a methylene spacer (s=2,4,6) [2].…”

“…It is well established that the presence of electrolytes in the ionic surfactant solutions reduces their cmc's[9][10][11][12]. due to the charge screening effect, which leads to a reduction in the Debye length[13,14]. As such (i.e., with decrease in the Debye length), the repulsive interactions between similarly charged head groups decrease and micelle formation is facilitated: this results in increase in surface activity and the consequent lowering of the cmc value.For 16-E2-16 gemini the cmc value decreases with the nature of the added counterion and the magnitude of this decrease follows the order: Sal − > Ben − > SCN − > NO 3 − > Cl −…”

Electrolyte effect on adsorption and the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture

“…When electrolyte is added to a system of charged catanionic vesicles, the maximum of the interaction potential can be decreased [11], and hence, the rate of specific aggregation can be increased; aggregation increases with decreasing electrostatic repulsion. The range of the electrostatic interaction is also decreased with increasing electrolyte concentration as given by the Debye length [11,12]. On the other hand; the studies show that molecular self-assembly in surfactant systems is largely dependent on the number of water molecules surrounding the headgroups.…”

Catanionic surfactant formation from the interaction of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and the ionic liquid 1-butyl-3-methylimidazolium octyl sulfate (bmim-octyl SO4) in aqueous solution

“…From the pioneering studies by Kaler on oppositely charged single tailed surfactants [29][30][31][32][33][34] numerous contributions have been reported on the spontaneous vesicle formation and micelle-vesicle transitions produced as a function of the surfactant ratio in the mixture [35][36][37][38][39][40][41]. Similar vesicle formation should be expected when a cationic surfactant is mixed with an ionic liquid displaying anionic surfactant-like behavior.…”