compatible and relatively low-cost material. Indeed, based on its chemical structure, we make the following hypotheses. First, it is possible to modify the cis double bond with various kinds of headgroups through relatively simple chemical reactions to achieve cost-effective synthesis. Second, it is possible to introduce a hydrocarbon chain at the terminal carbonyl group via the amide or ester bonding. These two synthetic strategies allow for the design of a wide variety of gemini surfactants

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... well as for the control of the hydrophilic/hydrophobic balance of the surfactants by variations in the hydrocarbon chain length and the type of headgroups. The oleic acid-based surfactants synthesized in our previous works include phosphate-type 5 and sulfonic-type 6 anions. In our current work, we have developed a new type of oleic acid-based gemini surfactant and studied the physicochemical properties as a function of the hydrocarbon chain length. These surfactants contain two carboxylic acid headgroups covalently bound to the cis double bond of oleic acid via disuccinyl units. The carboxylic acid head-Abstract: Anionic gemini surfactants with carboxylic acid headgroups have been synthesized from oleic acid. The hydrocarbon chain is covalently bound to the terminal carbonyl group of oleic acid via an ester bond, and the carboxylic acid headgroups are introduced to the cis double bond of oleic acid via disuccinyl units. The surfactants exhibit pH-dependent protonation-deprotonation behavior in aqueous solutions. In alkaline solutions (pH 9 in the presence of 10 mmol dm -3 NaCl as the background electrolyte), the surfactants can lower the surface tension as well as form molecular assemblies, even in the region of low surfactant concentrations. Under acidic (pH 3) or neutral (pH 6-7) conditions, the surfactants are intrinsically insoluble in aqueous media and form a monolayer at the air/water interface. In this study, we have investigated physicochemical properties such as the function of the hydrocarbon chain length by means of static surface tension, pyrene fluorescence, dynamic light scattering, surface pressure-area isotherms, and infrared external refl ection measurements.