Micelle to Lamellar Aggregate Transition of an Anionic Surfactant in Dilute Aqueous Solution Induced by Alkali Metal Chloride and Tetraalkylammonium Chloride Salts

Abstract

Micelles of the anionic surfactant sodium dodecylbenzenesulfonate (NaDoBS) in dilute aqueous solution can be transformed into lamellar aggregates by the addition of alkali metal chloride (LiCl to CsCl) and tetraalkylammonium chloride (alkyl is methyl or n-butyl) salts. Depending on the type of cation, concentration of salt, and isomeric purity of the alkyl chain of the surfactant, different types of phases are observed: large unilamellar vesicles, multivesicular vesicles, and flocculated multilamellar vesicles (lamellar droplets). Over limited concentration ranges, some salts induce phase separation in a surfactant-rich and a surfactant-lean phase. The formation of the different phases was monitored by turbidity and fluorescence depolarization measurements, whereas the phases were characterized by light microscopy, freeze-fracture electron microscopy, and confocal scanning laser microscopy. Thermodynamic aspects of aggregation, in particular the counterion binding characteristics, were studied by microcalorimetry and conductivity. On a molecular level, the packing in a lamellar array can be explained largely in terms of a change in counterion binding and, to a lesser extent, by a decrease of the hydration of the headgroup and the counterion. A better counterion binding is facilitated by a less hydrated cation or by an increase of the electrolyte concentration. The formation of different types of lamellar aggregates is due to different types of interactions between lamellar layers or between aggregates: largely repulsive for stable dispersions of unilamellar vesicles to attractive down to short distances for the flocculated lamellar droplets.

Hofmeister series and specific interactions of charged headgroups with aqueous ions

“…On the other hand, didodecyldimethylammonium acetate and hydroxide are highly water soluble and form an extended micellar phase. Similar counterion effects have been observed for the swelling of lamellar phases [67][68][69]. Many possible explanations for the observed phenomenon are given.…”

Enhanced electrochemical reduction of hydrogen peroxide on silver paste electrodes modified with surfactant and salt

“…This has been observed by Sein et al [42] with sodium dodecylbenzenesulfonate (NaDoBS) in the presence of several chloride salts. The CMC for DBSA is approx.…”

Aggregational Attitude of Hexadecyltrimethylammonium Bromide in Aqueous Solutions of Sodium Salt at 298.15k

“…increasing conductivity with concentration, which is generally observed for dilute solutions, was attributed to the increasing number of free HTA + and Br -ions in solution, whereas the small increase in the conductivity values above the CMC was attributed to two factors: (i) attraction of parts of counter-ions directly to micellar surface which resulted in effective loss of ionic charges making the counter-ions become dynamic part of the aggregated micelle which promote high surface charge and reducing the available ion carrier, (ii) the aggregated micelle contribute to the conductance better than the free ion that is less mobile [20]. The result presented in Table 2 showed that the CMC value of HTABr decreased with the addition of sodium salts, which is an indication that, the significant role of electrolytes in the micellization process, which is a characteristic behaviour of an ionic surfactant, is due to the layer formed at the air-solution interface [21][22][23].…”