Effect of Hydrophilic Groups of Ca Surfactants and Hydrophobic Chains of C_nDMAO on Coordinated Vesicle Formation

Abstract

The effects of hydrophilic headgroups of Ca surfactants, calcium dodecylsulfate (Ca(DS)(2)), calcium dodecylsulfonate (Ca(DSA)(2)), and calcium laurate (CaL(2)) and hydrophobic chains of alkyldimethylamine oxide (C(n)DMAO, n = 12, 14, 16) on the formation of Ca(2+)-ligand coordinated vesicles was investigated in detail. On the basis of phase behavior studies, rheological properties and freeze-fracture transmission electron microscope (FF-TEM) images were measured. Quite different phase behaviors were observed in different surfactant systems. For a Ca surfactant with a highly polar group, Ca(DS)(2), vesicles were observed in all Ca(DS)(2)/C(n)DMAO (n = 12, 14, and 16) systems, whereas for Ca surfactant with lower polar group, Ca(DSA)(2), vesicles can form in Ca(DSA)(2)/C(n)DMAO systems of n = 14 and 16 but not for n = 12. For CaL(2), the surfactant with the least polar group, vesicles form only in the CaL(2)/C(16)DMAO system. The results demonstrate that in the systems formed by Ca surfactants and C(n)DMAO, the formation of vesicles is driven not only by interaction between Ca(2+) and the N → O groups of C(n)DMAO but also by electrostatic and hydrophobic interactions. Vesicles prefer to form in Ca surfactants with highly polar headgroups and C(n)DMAO with long chain length.

Synergism and formation of vesicle gels in salt-free catanionic hydrocarbon/fluorocarbon surfactant mixtures

“…3). This phase sequence is consistent with those observed in many previously reported catanionic [10][11][12][13] and zwitterionic/ anionic [36][37][38][39] surfactant mixtures and should be ascribed to a change of the averaged critical packing parameter (p) 41 of the surfactant mixture upon the addition of TFOPA or HFDPA. It is well-known that if p # 1/2, globular or rod-like micelles normally form.…”

“…The high surface activity of TFOPA can be ascribed to the presence of the uorocarbon chain, which is consistent with the characteristics of the uorocarbon surfactants. [11][12][13][14] When the length of the uorocarbon chain was increased, as seen in HFDPA, the hydrophobicity of the molecule was enhanced and thus a much lower cmc of 2.07 Â 10 À5 mol L À1 was measured. At the same time, g cmc further decreased to a value of 17.48 mN m À1 .…”

“…In both cases, it was found that there are a large number of densely packed, polydisperse unilamellar vesicles coexisting with a smaller number of multi-lamellar vesicles, reminiscent of the spontaneous vesicle formation observed in catanionic and zwitterionic/anionic surfactant mixtures. [10][11][12][13][36][37][38][39] For the C 14 DMAO/TFOPA system, the size of the vesicles ranged from 90 to 273 nm with an average diameter of 174 nm. For the C 14 DMAO/HFDPA system, the vesicles ranged from 183 to 545 nm with an average diameter of 364 nm.…”

“…[5][6][7][8][9][10][11] A typical example is the mixture of a zwitterionic surfactant, alkyldimethylaminoxide (C n DMAO), with various fatty acids. [12][13][14] In such a system, the H + dissociates from the fatty acid and can charge C n DMAO to form a cationic surfactant (H + + C n DMAO ¼ C n DMAOH + ), which then associates with the carboxylate anion to form an ion pair. Driven by the hydrophobic/hydrophobic interaction between the alkyl chains and the electrostatic interaction between the hydrophilic headgroups, C n DMAO/fatty acid mixed systems exhibit strong synergism.…”

Metal-ligand coordinated Ca(DS)2/C14DMAO/H2O system: Phase behavior and rheological property

“…Thus, the distribution of metal ions exhibits the structures of the aggregates and they can be used as templates in preparation of functional materials. Our recent results [26] show that besides the metal-ligand interaction, the aggregation behavior is also affected by other factors, e.g., the hydrophobic interaction between the surfactant chains and the electrostatic interaction between the two surfactant headgroups. Therefore, the sizes, shapes and transition between diverse aggregates can be modulated by designing appropriate surfactant systems and controlling the external conditions, such as pH, temperature, and salinity.…”