Functional Characterization of a Novel Class of Gemini (Dimeric) Surfactants Synthesized from Sunflower Oil

The field of natural resource-derived products is gaining significant interest in the current global energy scenario. Natural surfactants or “surface-active agents” with favorable attributes find usability in myriad sectors comprising foaming and cleaning, corrosion inhibition, gelation, oil recovery, waste water treatment, biomedical research, textile processing and preparative chemistry. Growing need for indigeneity, ease of availability/manufacturability and cost-effectiveness, combined with novelty in “green” surfactant science is a pivotal area of concern. In present study, a novel class of self-assembling gemini surfactants with unique “dimer structure” were synthesized from plant-derived raw material, sunflower oil. Sunflower seed oil is rich in mono-unsaturated (oleic acid) and poly-unsaturated (linoleic acid) components, with small amounts of saturated fats. Non-ionic bis(monoglyceride-1-hydroxymethyl-2-fattyacidester)-α,ω-alkanediether surfactants with four and six methyl spacers were synthesized via a stepwise process: transesterification, followed by two stages of nucleophilic substitution (S_N2) reaction. The synthesized surfactants were characterized by FT-IR, ¹H-NMR and TGA studies. Surfactants retained their structural integrity under high temperature conditions. The surfactant molecules exhibited self-aggregation ability at low concentrations, resulting in low critical micelle concentration (CMC). Favorable interfacial behavior was observed at oil-aqueous interfaces. Addition of salt showed synergistic effects, resulting in ultralow interfacial tension (IFT) of the order of 10^−2 to 10^−3 mN/m. The gemini surfactant solution exhibited non-Arrhenius, pseudoplastic flow behavior, wherein viscosity increased with temperature due to greater degree of entanglement of worm-like micelles/aggregates to develop network structure in bulk solution. These formulated surfactants also formed stable oil-in-water emulsions with slow rate of oil droplet coaleascence, as observed from microscopic imaging. The surfactants, therefore, exhibited beneficial properties in terms of thermal stability, interfacial activity, viscosity behavior and emulsification. The sunflower oil based gemini surfactants, prepared from readily available and economical raw material, were successfully formulated as a promising alternative to synthetic, non-biodegradable surfactants that are commercially employed in industrial applications.