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

The phase transition of microemulsions involving the nonionic surfactant C1 2E5 [C12H25(OCH2-CH2)(5)OH], water, and alkanes (heptane, decane and tetrad ecane) has been investigated through the excimer formation of pyrene. On go ing to the microemulsion bicontinuous phase, by changing either composition or temperature, pronounced changes in the pyrene excimer-to-monomer fluore scence intensity ratio, I-E/I-M are observed. Several differences in the st eady-state emission spectra and in fluorescence decay curves show that as a probe pyrene is well suited to follow the transition from the water contin uous to the oil continuous phase, through an intermediate bicontinuous (con tinuous in both water and oil) region. The results provide information abou t the different characteristics and structure of these three regions (water continuous, bicontinuous, and oil continuous) of the phase diagram for C12 E5/water/alkane systems.