Monitoring the phase transition of C12E5/water/alkane microemulsions through excimer formation

The phase transition of microemulsions involving the nonionic surfactant C12E5 [C12H25(OCH2-CH2)5OH], water, and alkanes (heptane, decane and tetradecane) has been investigated through the excimer formation of pyrene. On going to the microemulsion bicontinuous phase, by changing either composition or temperature, pronounced changes in the pyrene excimer-to-monomer fluorescence intensity ratio, IE/IM, are observed. Several differences in the steady-state emission spectra and in fluorescence decay curves show that as a probe pyrene is well suited to follow the transition from the water continuous to the oil continuous phase, through an intermediate bicontinuous (continuous in both water and oil) region. The results provide information about the different characteristics and structure of these three regions (water continuous, bicontinuous, and oil continuous) of the phase diagram for C12E5/water/alkane systems. FCT financiamento plurianual do CFUM G.H. would like to thank the Fundação para a Ciência e a Tecnologia (PRAXIS XXI) for financial support, as would M. da G.M. and H.D.B. (Project 2/2.1/QUI/411/94).