Dilational Properties of Anionic Gemini Surfactants with Polyoxyethylene Spacers at Water−Air and Water−Decane Interfaces

Abstract

The dilational properties of anionic gemini surfactants (oligooxa)-alpha,omega-bis(m-octylbenzene sulfonate) (C(8)E(x)C(8)) with polyoxyethylene spacers at the water-air and water-decane interfaces were investigated via the oscillating barriers method. The influences of oscillating frequency and bulk concentration on dilational properties were explored. The interfacial tension relaxation method was employed to obtain dilational parameters in a reasonably broad frequency range. The experimental results show that the number of ethylene oxide groups is one of the principal factors to control the nature of the interfacial film. With an increase of ethylene oxide groups, the dilational modulus of C(8)E(8)C(8) shows two maxima with the increasing concentration. Furthermore, the dilational moduli at the water-decane interface are remarkably lower than those at the water-air interface for C(8)E(1)C(8) and C(8)E(4)C(8), while the dilational modulus at the water-decane interface is close to that at the water-air interface for C(8)E(8)C(8), which indicates that the structure of the adsorption sublayer plays a more important role. Possible schematic diagrams of adsorbed molecules with different polyoxyethylene spacers at the water-air and water-decane interfaces are proposed. The results of relaxation experiments and Cole-Cole plots can support our provided mechanism strongly.

Review on chemically bonded geminis with cationic heads: second-generation interfactants

“…A considerable number of investigations have been reported on the surface activity and aggregation behaviors of gemini surfactants. Usually a longer hydrophobic chain leads to higher surface activity (lower CMC), but some unexpected results have been found that contradict the typical monotonic ''longer'' to ''higher'' change [40,41]. Among these aberrant properties, one noteworthy phenomenon is that the CMC of some gemini surfactants increases when the chain length of the alkyl hydrophobic group goes beyond a critical length.…”

“…Among these aberrant properties, one noteworthy phenomenon is that the CMC of some gemini surfactants increases when the chain length of the alkyl hydrophobic group goes beyond a critical length. Thus, studies of the relationship between gemini structure and property are important, not only theoretically, but also from the practical stand point [41].…”

Surface dilatational properties of Gemini surfactants containing multiple hydroxyl groups

“…For both curves, there were two maxima at lower frequencies, which admit the occurrence of multiple relaxation processes owing to the longer time intervals between external disturbances. In fact, such dilatational behaviour has been discovered for some nonionic surfactants [37] and a Gemini surfactant with an ethylene oxide chain as the spacer [25]. The reason is attributed to the reorientation and compression of ethylene oxide chains in the interfacial layer [25]; however, the Gemini surfactant 12(2OH)-8-12(2OH) does not have a long ethylene oxide chain as either a hydrophilic head group or spacer; the explanation above may not be suitable.…”

“…In fact, such dilatational behaviour has been discovered for some nonionic surfactants [37] and a Gemini surfactant with an ethylene oxide chain as the spacer [25]. The reason is attributed to the reorientation and compression of ethylene oxide chains in the interfacial layer [25]; however, the Gemini surfactant 12(2OH)-8-12(2OH) does not have a long ethylene oxide chain as either a hydrophilic head group or spacer; the explanation above may not be suitable. Zana et al investigated the adsorption behaviour of alkanediyl-α,ω-bis(dimethylalkylammonium bromide) Gemini surfactants at an air/water interface [38].…”

“…They also revealed that Gemini surfactant has a stronger binding ability with gelatin than that of DTAB [24]. Zhang et al [25] studied anionic Gemini surfactants with polyoxyethylene spacers. The number of ethylene oxide groups was found to influence the nature of the interfacial film.…”