Comparison between Two Anionic Reverse Micelle Interfaces: The Role of Water–Surfactant Interactions in Interfacial Properties

Abstract

In this work we have revisited the water/sodium bis-(2-ethylhexyl) phosphate (NaDEHP) reverse micelle system using, for the first time, molecular probes in order to investigate valuable interface properties. We have studied the solvatochromic behavior of 1-methyl-8-oxyquinolinum betaine (QB) and 6-propionyl-2-(N,N-dimethyl) aminonaphthalene (PRODAN) in water/NaDEHP/toluene system and, the results were compared with those obtained in water/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/toluene reversed micelles media. We have used absorption spectroscopy for QB and, absorption and emission spectroscopy for PRODAN. We choose those molecular probes because of they are sensitive to different effects thus we have obtained very significant information on the reversed micelles media. Our results demonstrate that because of the different water ? surfactant interactions the micropolarity, microviscosity, interfacial water structure, molecular probes partition and intramolecular electron transfer processes are dramatically altered for NaDEHP reversed micelles interfaces in comparison to the AOT systems. Because of the aromatic organic non polar solvent penetration to the interface, NaDEHP reversed micellar media offers an interface with lower micropolarity and microviscosity than AOT media. Also, the interfacial water in the NaDEHP system shows enhanced water-water hydrogen bond interaction in comparison with bulk water. The differences were manifested when these RMs interfaces were used to control from which excited state PRODAN can emit. AOT RMs interface represents the unique environment for PRODAN to undergo dual emission.