Interfacial Properties of Unsymmetrical Bolaform Amphiphiles with One Ionic and One Nonionic Head Group

Effect of Ionic Strength on the Interfacial and Bulk Properties of Unsymmetrical Bolaamphiphiles

“…Many previous studies have combined theoretical and experimental research in order to understand the active and passive control of surface and bulk properties of bolaamphiphiles that possess a hydrophobic domain and two polar head groups [1][2][3][4][5]. It has been demonstrated that the presence of a hydrophilic group at the x position within the surfactant structure affects the molecular forces acting in the system, which results in different bulk and surface properties of unsymmetrical bolaamphiphile surfactants compared to classical ionic surfactants [3,4,6]. The principal conclusions that emerges from past experimental studies of (11-hydroxyundecyl)trimethylammonium bromide (HTAB) [6], OH(CH 2 ) 11 N + (C 2 H 4 ) 2 (CF 2 ) 5 CF 3 I -(FHUB) [4] as well as a molecular thermodynamic model of the Gibbs monolayers of the redox-active surfactant Fc(CH 2 ) 11 N + (CH 3 ) 3 [3], where Fc is ferrocene, are as follows: (1) these surfactants tend to occupy larger areas at the interface with higher limiting surface tensions and critical micelle concentration (cmc) values; (2) the dominant contribution to the lowering of the surface tension comes from the configurational term, not the electrostatic repulsion; and (3) these systems are less sensitive to variations in the ionic strengths of the aqueous solutions compared to classical ionic surfactants [2][3][4][5][6].…”

“…Surface tension measurements of HTAB, FHUB and Fc(CH 2 ) 11 N + (CH 3 ) 3 as a function of added salt reveal that the surface tension of this class of surfactant is less sensitive to the ionic strength of the aqueous solution than the classical ionic surfactant sodium dodecyl sulfonate (SDS) [3,4,6]. From studies of HTAB, FHUB and Fc(CH 2 ) 11 N + (CH 3 ) 3 and the results of a molecular thermodynamic model [6], we have concluded that these unsymmetrical bolaamphiphiles have a weakly hydrophilic group at the x position, and that electrostatic interactions do not, in general, dominate the interfacial properties of this class of surfactant. Based on the studies above, we compare and contrast how adding salt affects the interfacial properties of a series of unsymmetrical bolaamphiphiles with strong hydrophilic groups at the x position, as shown in Fig.…”

Synthesis of Unsymmetrical Bolaform Surfactants with a Sulfonate Group and a Carboxyl Group

“…5. As predicted, these surfactants exhibit unusually low surface tensions, about 20 mN m -1 , equal to or even lower than that of some fluorocarbon surfactants [1][2][3][4][5][6], let alone that of hydrocarbon surfactants. Moreover, the surface tension measurements of these surfactants indicate the existence of two discontinuities, referred to as the 'first CMC' and the 'second CMC', similar to the conventional bolaform surfactants [12,13].…”

“…Considerable theoretical research on bolaform surfactants have been reported [1][2][3][4][5]. From these studies, it is described that the bolaform surfactants possess a looped configuration, which looks like the letter ''U'' standing on its heads at the air/water interface.…”

Recent advances in the mixed systems of bolaamphiphiles and oppositely charged conventional surfactants

“…Fig. 4a) when both the polar ends have to attach to water and the hydrocarbon spacers protrude into the air [11][12][13][14][74][75][76][77]. As a result, the outmost groups at the air/water interface are CH 2 from the spacer of the bolas instead of CH 3 from the conventional surfactants.…”