Self-assembly mechanism and application performance in aqueous solutions mediated by ethylene oxide chains in alcohol ether carboxylates and cocamidopropyl betaine

Abstract

Zwitterionic Cocoamidopropyl Betaine (CAB) and anionic alcohol ether carboxylates have garnered significant attention within the realms of green and colloid chemistry owing to their inherent biocompatibility, multi-responsiveness, and diverse applications. Systematic inquiry into the physicochemical properties, self-assembly mechanisms, and application efficacy of complex systems comprising alcohol ether carboxylate salts with varying ethylene oxide (EO) units (AECnH, n = 5, 7, 9) and CAB-35 in aqueous solutions was undertaken. It was discerned that the optimum physicochemical attributes of the complex system are attained at a molar ratio of AEC of 0.5 (αAEC = 0.5). Incremental augmentation in the number of EO units facilitated the formation of rod-like micelles, exhibiting relatively unstable characteristics, while a reduction in the number of EO units led to the generation of comparatively stable spherical micelles. The self-assembly of micelles in these hybrid systems predominantly hinges upon hydrogen bonding, electrostatic interactions, and hydrophobic forces. Furthermore, kinetic analysis validated that the genesis of micelles in all three hybrid systems is propelled by enthalpy, with the adsorption process entailing a mechanism characterized by mixed diffusion-kinetic adsorption. The optimal wetting performance of the complex system was observed at αAEC = 0.5, while the foam performance demonstrated a diminishing trend with escalating αAEC. This comprehensive discourse delineates the synergistic mechanisms and application efficacy of two distinct classes of green surfactants with disparate charges in aqueous solutions, while contemplating the influence of varying numbers of ethylene oxide chains. Not only does it furnish fundamental insights into their properties, but it also proffers a novel standpoint for the exploration of green surfactants.