Micellar Characteristics and Surface Properties of Some Sulfobetaine Surfactants

Abstract The micellar and interfacial properties of three sulfobetaine surfactants of the type C n H 2n+1 N + Me 2 (CH 2 ) 3 SO 3 − (n = 10; SB3-10 n = 12; SB3-12, n = 16; SB3-16) have been studied by conductometry and surface tension measurements. The critical micellar concentration (CMC), surface excess concentration (Γ max ), minimum surface area per molecule of surfactant (A min ), Gibbs free energy of micellization (ΔG o m ), Gibbs energy of transfer (ΔG o trans ), the surface pressure at CMC (π CMC ) and the Gibbs energy of adsorption (ΔG o ads ) of these surfactants have also been determined. Effect of formamide has been studied at higher temperature conductometrically. Results show that alkyl chain length and the amount of solvent composition influences micellization and surface properties of sulfobetaines. Increment in the CMC, ΔG o m and ΔG o trans , can be accounted for changes in the polarity of the bulk phase. Γ max , and π cmc decreases where as A min increases with increase in the organic solvent. It was also observed that micellization in water-formamide mixture was even slower than in the case of ethylene glycol.