Self-organization at the interface and in aqueous solution of a cationic gemini surfactant from the dioctyl ester of cystine

• Published in: Journal of colloid and interface science 2012-02, Vol.367 (1), p.319-326
• Main Authors: Angayarkanny, S., Vijay, R., Baskar, Geetha, Mandal, A.B.
• Format: Article
• Language: English
• Subjects: Adsorption; Adsorption isotherms; aqueous solutions; Cationic; cationic surfactants; Chemistry; Colloidal state and disperse state; Cystine; Cystine - chemistry; dissociation; emissions factor; energy; Esters; Esters - chemistry; Exact sciences and technology; fluorescence; Fluorometry; Fluroprobes; Gemini surfactants; General and physical chemistry; Interfacial characteristics; Langmuir film balance; Mathematical models; Micelles; Micelles. Thin films; microscopy; molecular models; Surface chemistry; Surface physical chemistry; surface tension; Surface-Active Agents - chemistry; Surfactants; Thermodynamics; viscoelasticity; Water - chemistry; wavelengths
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.10.043

[Display omitted] ► Dioctyl ester of cystine hydrochloride (DOEC) forms stable viscoelastic films at the air–water interface. ► CMC is about one order lower than the equivalent anionic surfactant from cystine. ► The molecular cross-sectional area at the interface was measured as 0.70±0.01nm2molecule−1. ► DOEC exhibits a tilted conformation at the interface, and the large packing parameter P of 0.58 suggests the formation of elongated micelles. ► DOEC favors one-dimensional growth to form fibril like structures. 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±0.27×10−5moldm−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 (ΔGm°) and adsorption (ΔGa°) were calculated to be −25.07 and −44.37kJmol−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 (λemi.) maximum down to 470nm 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 0.69nm2molecule−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.