Condition dependent self-aggregation behavior of aerosol-OT in mixed water-alcohol media: Physicochemical investigation

• Published in: Journal of molecular liquids 2022-05, Vol.354, p.118893, Article 118893
• Main Authors: Pan, Animesh, Phani Kumar, Bandaru V.N., Mati, Soumya S., Mal, Arpan, Prameela, Gorthy K.S., Aswal, Vinod K., Moulik, Satya P.
• Format: Article
• Language: English
• Subjects: Aerosol-OT (AOT); Micelles; Mixed solvents; RAGAs; Self-aggregation; Vesicles
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2022.118893

[Display omitted] •The aggregation behavior of Aerosol-OT in mixed aquo-organic solvent media from 0 to 100 vol% has been investigated.•Herein, the mixed aquo-ethanol (ET-W) and aquo-isopropanol (IP-W) solvent media have been taken into consideration.•The physicochemistry of AOT at the air/solvent interface, and its assembly formation in the bulk have been evaluated.•At higher vol%, the formation of “randomly arranged globular assembly” (RAGA) prevailed instead of reverse micelle (RM). Amphiphiles aggregation in mixed aquo-organic solvent media has profound interest in the fields of chemistry, biology, pharmaceutics, and industry. Detailed fundamental understanding of the process in the bulk and at the interface is still remaining to be explored. In this report, the effect of two water miscible alkanols (ethanol (ET), and isopropanol (IP)) on the aggregation-behaviors of the surfactant sodium dioctylsulfosuccinate (Aerosol-OT or AOT) has been studied in a wide range of alcohol proportions (0 to 100 vol%) in water. Different physicochemical parameters like critical micelle concentration (CMC), counter-ion binding (β) and aggregation number (Nagg) of micelles, and the energetics of the AOT adsorption at the air/water interface, and its assembly formation in the bulk have been evaluated employing tensiometry and isothermal titration calorimetry (ITC) methods. The micelle forming region of AOT has been found to be 0–30 vol% for ET, and 0–20 vol% for IP. At [solvent] > 30 vol% the possibility of formation of “randomly arranged globular assembly” (RAGA) of the amphiphile [1] prevailed. Role of different solvent parameters have been attempted to explain the thermodynamics of the micellization process of AOT. SANS experiments have supported vesicle formation of concentrated solutions of AOT in 50 vol% ET or IP in water; with increasing alcohol vesicles transformed into micelles. DFT (density functional theory) calculations have been made for understanding the intermolecular interactions in AOT-H2O-ET or IP systems compared to their binary mixtures (AOT-H2O; AOT-ET; AOT-IP). NMR study has supported favorable interactions of the alkanols (ET and IP) with the head group of the AOT. Formation of micelles and reverse micelles by AOT in different composition of alcohols and pure alcohols reported by Michor and Berg [2] has been reasoned out to be incorrect.