Solubilization of an Organic Solute in Aqueous Solutions of Unimeric Block Copolymers and Their Mixtures with Monomeric Surfactant: Volume, Surface Tension, Differential Scanning Calorimetry, Viscosity, and Fluorescence Spectroscopy Studies

Abstract

The ability of aqueous systems, formed by unimeric copolymers and their mixtures with a monomeric surfactant, in solubilizing large quantities of 1-nitropropane (PrNO2) was explored. The copolymers are F68 and L64, which differ for the hydrophilicity, and the surfactant is sodium dodecanoate. For a better understanding of the mechanism of solubilization, thermodynamic (volume and differential scanning calorimetry), spectroscopy (steady-state fluorescence), viscosity, and interfacial investigations were carried out. PrNO2 causes the micellization of the unimeric copolymer, and the required amount of PrNO2 depends on the composition, the copolymer nature, and the temperature. Large quantities of PrNO2 form mixed micelles where PrNO2 experiences an environment similar to its pure liquid state. The presence of the additive allows a decrease of the critical micellar temperature, evidence of which is quantitatively explained through a novel thermodynamic approach. A synergistic effect in solubilizing PrNO2 was observed when surfactant monomers were added to the unimeric copolymer solutions. The increased amount of PrNO2 leads to the complete self-assembling of both the copolymer and the surfactant; a process favored by temperature increase. For all of the investigated systems, the presence of PrNO2 generates a viscosity increase.