Three counterion coupled gemini (cocogem) surfactants in the series 1,6‐bis(N,N‐alkyldimethylammonium) adipate, referred as n‐6‐n (n = 12, 14, 16), were synthesized, purified and characterized by 1H NMR and 13C NMR. Their physicochemical properties were investigated by electrical conductivity and surface tension measurements. The degree of ionization, critical micelle concentration (CMC), surface excess at the air/solution interface (Γmax), minimum area per surfactant molecule at the air/solution interface (Amin), surface tension at the CMC (γCMC), and pC20 (negative log of the surfactant molar concentration, required to reduce the surface tension of water by 20 mN m−1) were calculated. Increase in tail length of the surfactants increases the efficiency of surfactants to decrease the surface tension of water. Thermodynamic parameters, viz. molar free energy at the maximum adsorption attained at CMC (Gmin), standard Gibb's energy of micellization (), and standard Gibbs energy of adsorption (), were also calculated. The and values show that the monomers were preferred to be adsorbed at the air/water interface and then in the micellar formation in the bulk. Additionally, fluorescence measurements were used to find the aggregation number. Other relevant surface properties (Krafft point, emulsion stability, foaming ability, micellar stability and dye solubilization ability) were also evaluated. These results suggest that with respect to emulsion formation, micellar stability and dye solubilization, the cocogem with a 16‐carbon chain gives better results, producing 89 % more stable foams and shows better aggregational behavior.

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Amitriptyline Hydrochloride / Zwitterionic Gemini Surfactants / Surface Tension / Mixed MicellesThe physicochemical properties, viz, critical micelle concentration (cmc), surface excess concentration (Γ max ), minimum area per head group ( A min ) of zwitterionic surfactants (designated as n(−)-2-m(+); n = 8, 10, 12 and m = 12, 14, 16) and their mixtures with amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) were determined by using surface tension measurements. The cmc and ideal cmc (cmc id ) values along with interaction parameters, β m and β σ (calculated using Rubingh's and Rosen's models), suggest attractive interactions among the components. The Krafft temperature measurements also indicate strong attractive interactions. Γ max (or A min ) increases (or decreases) with the addition of gemini surfactant; the values being closer to that of the drug. These values and micellar mole fraction (X m 1 -calculated from Rubingh's model and X Moto 1 -calculated from Motomura's model) indicate larger contribution of gemini surfactants in mixed micelles and smaller contribution at air/solution interface (as mole fraction values at interface, X σ 1 , are slightly smaller than X m 1 ). The standard Gibbs energy of micellization (ΔG • mic ) and adsorption (ΔG • ad ) as well as excess energy of mixing (ΔG m ex ) are all negative. All these results suggest higher stability of the mixed systems. UV absorbance results also suggest that the mixed micelles are stable for several days.

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The micellization process in mixtures of amphiphilic drugs and asymmetric dimeric zwitterionic surfactants have been investigated tensiometrically. The drugs used are from two families: imipramine hydrochloride (IMP)-a tricyclic antidepressant and ibuprofen (IBF)-a nonsteroidal antiinflammatory drug, whereas zwitterionic dimeric surfactants are heterogemini surfactants that contain quaternary ammonium and phosphate groups as heads. The results show that the cmc of drug-surfactant mixtures decreases with the increase in stoichiometric mole fraction of surfactants (a 1 ), suggesting attractive interaction among the two components. This is supported by the values of cmc id (critical micelle concentration values for ideal mixing) which are always greater than experimental cmc values. Also, the decrease in magnitude is more in IBF-dimeric surfactant mixed systems than in IMP-dimeric surfactant mixed systems. Micellar mole fraction values, obtained using Rubingh's (X m 1 ) and Motomura's (X m 1 ) models, are lower than the micellar mole fraction for ideal mixing (X id 1 ). The micellar interaction parameter (b m ) follows the order: 8(. The results are explained on the basis of difference in tail lengths. Interfacial mole fraction (X r 1 ) values, evaluated using Rosen's model, are higher than X m 1 values for IMP-10(-)-2-16(?) and IMP-10(-)-2-14(?) systems while for all other systems (except 8(-)-2-14(?)) the values are smaller than X m 1 . The interaction parameter at the interface (b r ) is negative and b m av values are greater than b r av in magnitude. All the results indicate that the dimeric surfactants are mostly in cationic form.