Resumo:
Microemulsions are thermodynamically stable and macroscopically homogeneous systems composed of water, oil, surfactant, and co-surfactant. Usually, these surfactants are synthesized from petroleum derivatives and, therefore, have undesirable environmental characteristics, such as low biodegradability and high toxicity, which has motivated the development of more environmentally friendly alternatives. In this context, the present study investigated the formation of microemulsions containing water, an ethoxylated nonionic surfactant and an oil, both derived from cardanol, a compound extracted from the cashew nutshell liquid, as well as co-surfactants. The compositions in which microemulsions were formed have been determined by constructing pseudoternary phase diagrams (water/oil/surfactant:co-surfactant), upon varying the co-surfactant type between ethanol, 1-butanol, and 1-octanol. The obtained formulations were characterized through visual observations of their macroscopic aspects and by measuring electrical conductivity, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and X-ray photon correlation spectroscopy (XPCS). Aiming for practical application of the obtained microemulsions, some compositions were tested for their potential to disperse oil spills in water. These tests were performed on a laboratory scale using turbidity measurements and stability tests under centrifugation and light dispersion. The analysis of the obtained diagrams revealed that 1-butanol induced the formation of microemulsions over a wider range of compositions compared to the other two co-surfactants employed. DLS results indicated that the average droplet size in the microemulsions was below 10 nm, and conductivity measurements revealed microemulsions of the water-in-oil or bicontinuous type, depending on the co-surfactant used. SAXS and XPCS measurements provided structural data and information on the dynamics of the aggregates within the microemulsions, respectively. The oil dispersion efficiency tests indicated that the bicontinuous microemulsions, formed only in the presence of 1-butanol, were more effective compared to aqueous surfactant solutions at the same concentration. Collectively, the results demonstrated for the first time the elucidation of the phase behavior of the investigated surfactant in mixtures with oil and water, as well as the feasibility of applying the obtained systems to solve an environmental problem, thus contributing to the development of more efficient and sustainable products.
