Lyotropic and interfacial behaviour of an anionic gemini surfactant

Area of Science:

• Surfactant chemistry
• Physical chemistry
• Materials science

Background:

• Dimeric surfactants, or gemini surfactants, offer unique properties compared to conventional surfactants.
• Anionic gemini surfactants are less explored than their cationic counterparts.
• Understanding lyotropic phase behavior is crucial for surfactant applications.

Purpose of the Study:

• To characterize the lyotropic phase behavior of the sodium salt of N,N'-hexane-bis (1-dodecen-1-ylsuccinamic acid).
• To determine the phase diagram of this anionic gemini surfactant in water at various temperatures.
• To measure the interfacial tension at the n-heptane/water interface and analyze surfactant properties.

Main Methods:

• Lyotropic phase behavior was investigated using flooding penetration scans.
• Phase diagrams were constructed for surfactant-water mixtures from 20°C to 100°C.
• Interfacial tension measurements were performed at the n-heptane/water interface.

Main Results:

• A sequence of lyotropic phases (micellar, normal hexagonal (H1), cubic (V1), lamellar (Lalpha)) was observed.
• This phase sequence remained consistent across the studied temperature range (20-100°C).
• The surfactant exhibited a large head group area (2.8+/-0.3 nm2) and low interfacial tension (7 mN m(-1)) at the n-heptane/water interface.

Conclusions:

• The anionic gemini surfactant displays predictable lyotropic phase behavior over a wide temperature range.
• The surfactant's interfacial properties are significant, though its interfacial tension is higher than reported for some cationic gemini surfactants.
• Further research into anionic gemini surfactants could reveal novel applications.