Self organisation behaviour at the interface and in aqueous solution of the cationic gemini surfactants from dioctyl ester of cystine

Abstract

The cationic surfactant, dioctyl ester of cystine hydrochloride (DOEC), was characterized for interfacial adsorption and aggregation behavior in water. The cmc of DOEC was measured as 1.42 ± 0.27 × 10^-5 mol dm^-3 using the techniques of tensiometry, conductivity and fluorimetry. From specific conductivity measurements, the degree of dissociation (α ) of the amine hydrochloride was measured as 0.612. The standard free energy change of micellization (Δ G_m^o)and adsorption (Δ G_a^o)were calculated to be -25.07 and -44.37 kJ mol^-1, respectively. The aggregated structures provide non-polar microdomains as inferred from the I₃/I₁ emission intensity ratio of 1.05 of pyrene fluoroprobe and also a blue shift of fluorescence emission wave length (λ _emi.) maximum down to 470 nm with enhanced intensity of ANS probe in micellar solutions. From Langmuir film balance experiments, it is shown that DOEC forms stable viscoelastic films at the interface with A₀ at 0.69 nm² molecule^-1 that agree with the result from surface tension measurements. Molecular modeling suggests the tilted orientation of DOEC at the interface. A large packing parameter (P) of 0.58 and the fibril structures as observed from microscopy studies demonstrate that DOEC favors one-dimensional growth to form elongated micelles.