Gels from surfactant solutions with densely packed multilamellar vesicles

Abstract

Results on surfactant gels containing densely packed multilamellar vesicles are reported. The gels form spontaneously when the bilayers of L, or L, phases of alkyldimethylaminoxide and cosurfactant are charged up by the addition of ionic surfactant or HCl. The rheological behaviour on addition of excess salt was studied by dynamic rheological measurements for systems with surfactants of different chainlengths. Both the storage modulus, G', and the yield stress, u y , decay with rising salinity. This effect is caused by the reduction of both the electrical contribution of the bending constants of the bilayers and the compression modulus of the vesicles. The influence of the charge density on the rheological properties was determined. G' and by increase with charge density and reach a plateau that depends on the chainlength of the surfactant. Measurements on samples prepared with waterglycerol mixtures show that the moduli and the yield stress value are independent of the solvent viscosity. Photographs of the surfactant gels that were taken with the interference contrast microscopy technique are presented. They reveal that some of the vesicles are much bigger than expected on the basis of TEM micrographs. The mean size of the vesicles can be estimated on basis of conductivity data. This method yields an average number of 5-6 shells per vesicle and corresponds with the value taken from the electron micrograph. The rheological data are explained with a model that was recently introduced by van der Linden. In connection with a model due to Lekkerkerker for the electric contribution of the bending constant of the bilayers and our own calculations of the osmotic pressure the van der Linden formula yields good results for describing the experimental data.

Behavior of Ionically Charged Lamellar Systems under the Influence of a Shear Field

“…In our system, vesicles are easily formed by addition of the cationic surfactant tetradecyltrimethylammonium bromide (TTABr) to the ternary system tetradecyldimethylamineoxide TDMAO/1-hexanol/water ( Figure 2). [25][26][27][28] The total surfactant concentration was always 100 mM, and different phases can be adjusted by variation of the content of the cosurfactant hexanol. The phase sequence in the ternary Schematic quaternary phase diagram of zwitterionic tetradecyldimethylamineoxide (TDMAO), cationic tetradecyltrimethylammonium bromide (TTABr), 1-hexanol, and water at 25°C.…”

A novel viscoelastic system from a cationic surfactant and a hydrophobic counterion

“…The formation of vesicles from binary systems or morecomponent systems was observed for nonionic surfactants with hydrophobic chain or sugar surfactants with a small head group, nonionic surfactants with two hydrophobic chains, cationic or anionic surfactants with two long alkyl chains, mixtures of cationic and anionic single-chain surfactants, mixtures of amino acid surfactants or amino acid surfactants at intermediate pH values, perfluoro surfactants with two hydrophobic chains, mixtures of cationic perfluoro and anionic hydrocarbon surfactants, mixtures of cationic/anionic and zwittterionic perflouro surfactants or nonionic perfluoro surfactants, mixtures of surfactants with cosurfactants, and mixtures of perfluoro surfactants with cosurfactants or with perfluoro cosurfactants [23][24][25][26][27][28][29]. Unilamellar vesicles can be prepared also from the lamellar phase by shear [30][31][32][33].…”

Investigations of vesicle gels by pulsed and modulated gradient NMR diffusion techniques

“…Such behaviour has for instance been observed for densely packed multilamellar vesicles. [5][6][7] However, it has also been observed that unilamellar vesicles composed of anionic surfactant, cosurfactant, and water can form such a vesicle gel spontaneously. These systems are viscous and according to previous experimental investigations they consist of monodisperse unilamellar small vesicles with a radius of about 15-25 nm.…”