Self-assembly of cationic surfactant in choline chloride-based deep eutectic solvents: structural solvation and dynamics

Abstract

Deep eutectic solvents (DESs) have gained popularity in various applications due to their improved environmental sustainability and biodegradability. For the present study, several polyhydric alcohols, including ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and glycerol (Gly), have been used as hydrogen bond donors (HBDs) and choline chloride (ChCl) as a hydrogen bond acceptor (HBA) in a fixed molar ratio to form a homogenous and stable DES. Controlled water mixing into such neat DESs has always been thought to be a quick and efficient method to tune the chemical and thermodynamic properties of DESs. The structural solvation and dynamics of the prepared DESs with the inclusion of water vary from low to high water concentrations that have been examined employing Fourier transform infrared (FT-IR), and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Herein, the micellization behavior of a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), in neat DESs and DES–water mixtures has been demonstrated by using tensiometry, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. Furthermore, it has been observed that DESs exhibit an ample thermodynamic driving force for creating micelles, since they contain an H-bonded nanostructure. However, such self-assembly appears to be very much dependent on DESs, the amount of water, and the surfactant used. A computational simulation approach using a semiempirical method is put forth employing the Gaussian 09 W calculation window in the Gauss View 5.0.9 software package. In addition, this study includes the determination of several optimized descriptors that intend to offer an in-depth examination of the surfactant–DES interactions.