Micelles in Mixtures of Sodium Dodecyl Sulfate and a Bolaform Surfactant

Abstract

Mixtures composed of water, sodium dodecyl sulfate (SDS), and a bolaform surfactant with two aza-crown ethers as polar headgroups (termed Bola C-16) were investigated by modulating the mole ratios between the components. The two surfactants have ionic and nonionic, but ionizable, headgroups, respectively. The ionization is due to the complexation of alkali ions by the aza-crown ether unit(s). Structural, thermodynamic, and transport properties of the above mixtures were investigated. Results from surface tension, translational self-diffusion, and small angle neutron scattering (SANS) are reported and discussed. Interactions between the two surfactants to form mixed micelles result in a combination of electrostatic and hydrophobic contributions. These effects are reflected in the size and shape of the aggregates as well as in transport properties. The translational diffusion of the components in mixed micelles, in particular, depends on the Bola C-16/SDS mole ratio. Nonideality of mixing of the two components was inferred from the dependence of the critical micelle concentration, cmc, on the mole fraction of Bola C-16. This behavior is also reflected in surface adsorption and in the area per polar headgroup at the air-water interface. SANS data analysis for the pure components gives results in good agreement with previous findings. An analysis of data relative to mixed systems allows us to compute some structural parameters of the mixed aggregates. The dependence of aggregation numbers, nu(T), on the Bola C-16/SDS mole ratio displays a maximum that depends on the overall surfactant content and is rationalized in terms of the nonideality of mixing. Aggregates grow perpendicularly to the major rotation axis, as formerly observed in the Bola C-16 system, and become progressively ellipsoidal in shape.

Characterization and stability of catanionic vesicles formed by pseudo-tetraalkyl surfactant mixtures

“…When a 1 ¼ 0.1, for instance, b is close to À11 k B T. It is worth noticing, in addition, that b values in Table 2 are very similar to those reported in the literature for structurally related catanionic mixtures. 45 The free energy of aggregation of catanionic systems is always more negative than the pure surfactants, indicating a substantial propensity to form mixed aggregates. When the contributions to the Gibbs energy are only ascribed to the alkyl chains, DG agg should regularly scale with molar ratios.…”

In vitro and in vivo evaluation of Bola-surfactant containing niosomes for transdermal delivery

“…Bola-surfactant is not able per se to form stable bilayer structures, such as vesicles, but micelles and rod-like micelles are formed when Bola-surfactant is dispersed in water (Eggers et al, 2003;Muzzalupo et al, 2006). In a previous investigation (Muzzalupo et al, 2005), it was shown that vesicles were formed when Bola-surfactant was mixed with Chol, thus achieving niosome colloidal suspensions.…”

Surfactant Mixtures: Performances vs. Aggregation States

“…X's are the mole fraction of the given surface-active species. In the limits dictated by the regular solution theory [48], the solute-solute interaction parameter, b, results to be [47].…”

“…In this way, the difference in composition between molecular and micellar form is immaterial. In two-component surfactant mixtures, thus, the cmc of the mixed system is defined according to the relation [47].…”