Self-association and micro-environmental properties of sodium salt of ibuprofen with BRIJ-56 under the influence of aqueous/urea solution

Herein, the interactions between the sodium salt of ibuprofen (IBU) with nonionic surfactant-BRIJ-56 were investigated at the interface as well as in the bulk phase (solution) in the existence and nonexistence of urea (250 mM). In the present study, tensiometric and fluorometric techniques have been utilized to investigate the association and micro-environmental properties of mixed systems. Various models (such as Clint, Rubingh, Maeda, etc.) were employed to obtain information regarding the nature of interaction between the components in bulk as well as at the interface. The critical micelle concentration (cmc) of pure amphiphiles and their mixed system increases in the existence of urea due to enhancement in the surface charge of the micelles. The urea activities have been explored on account of diverse aspects, such as the salvation of head groups and hydrophobic interactions. The aggregation number, micropolarity, and apparent dielectric constant of pure and mixed systems were investigated using steady-state fluorescence spectroscopy. A variety of energetic parameters (for instance the standard Gibbs free energy of micellization, Gibbs free energy of adsorption, and Gibbs excess energy) have been evaluated for further insight of urea action. The Δ values achieved are all negative, both in the absence and in the presence of urea.