Quaternary Ammonium Bromide Surfactant Oligomers in Aqueous Solution:  Self-Association and Microstructure

Abstract

Surfactant oligomers are made up of x (g2) amphiphilic moieties connected at the level of, or close to, the headgroups by spacer group(s). This paper examines the effect of the degree of oligomerization x on the self-assembling of cationic surfactant oligomers at interfaces and in the bulk. The quaternary ammonium bromide surfactant oligomers investigated are made up of dodecyldimethyl-and dodecylmethylammonium bromide moieties connected by short polymethylene spacers -(CH2)s-(of carbon number s). The properties investigated are the surface occupied by the surfactant at the air/solution and silica/solution interfaces, the critical micellization concentration (cmc), the micelle ionization degree at the cmc, the micelle micropolarity and microviscosity, and the microstructure and rheology of the solution. As x is increased, the surfactant layers at interfaces become more dense, the cmc decreases, the micelle microviscosity increases, the micelle shape for oligomers with s ) 3 changes from spherical (x ) 1) to wormlike (x ) 2), branched wormlike (x ) 3), and ring like (x ) 4). Last the zero-shear viscosity of the oligomer aqueous solutions starts to increase very rapidly and by orders of magnitude at surfactant concentrations above a value C* that decreases as x is increased. On the contrary the micelle ionization degree at the cmc and micelle micropolarity are nearly independent of x. These results are discussed in terms of surfactant packing parameter. They emphasize once more the possibilities offered by surfactant oligomers in obtaining surfactant organized assemblies with new architectures and solutions with improved and adjustable properties.

Dimeric (Gemini) Surfactants: Effect of the Spacer Group on the Association Behavior in Aqueous Solution

“…• (C 12 ), for two series of oligomeric surfactants (34). These values were calculated with the available cmc and ionization data, using the appropriate equation (35).…”

“…The adsorption isotherms of dimeric 12-s-12 (50-52), trimeric 12-s-12-s-12 (34,53), and tetrameric 12-3-12-4-12-3-12 cationic surfactants on macroporous amorphous silica showed that the adsorption involves two steps, as for conventional surfactants (34). The first step occurs at very low concentration and corresponds to a binding of individual dimeric surfactants to charged sites on the silica surface by an ion-exchange mechanism.…”

Adsorption of Ionic Surfactants on Solid Particles Determined by Zeta-Potential Measurements: Competitive Binding of Counterions

“…[4]; the result is K 1 = 359 and 497 M −1 for spherical and angular particles, respectively. Since in our experiments c 1s can be ≥3 × 10 −3 M (see Fig.…”

“…Various techniques have been applied to measure the depletion effect: colorimetric titration methods (1)(2)(3)(4), static (5)(6)(7) and dynamic (8) surface-tension experiments, UV spectroscopy (9)(10)(11), fluorescence (12), and high-pressure liquid chromatography (13) [see also studies cited in Ref. (2)].…”

Synthesis and monolayer film of a series of new twin-tailed gemini cationic surfactants at the air/water interface

“…Within this series, cationic gemini surfactants have been most widely investigated due to their favorable physicochemical properties [1,2]. However, most of the published results concentrate on dimeric quaternary ammonium salts [2], and occasionally on trimeric and tetrameric surfactants [8][9][10] and multi-armed oligomeric cationic surfactants that have 4 or 6 quaternary ammonium sites [11]. To the best of our knowledge, however, the quaternary ammonium geminis that possess four hydrophobic tails, each two of which are attached to one of the two hydrophilic heads, have been less well documented [12,13].…”