A LUMINESCENCE QUENCHING STUDY OF A PERCOLATION TRANSITION IN A PROPANE DIDODECYLDIMETHYLAMMONIUM BROMIDE WATER MICROEMULSION

Luminescence quenching was used to explore the interdroplet exchange processes for a propane/didodecyldimethylammonium bromide/water microemulsion at a dispersed-phase volume fraction of 0.30. This system shows a percolation type of transition in electrical conductivity as the pressure of the liquid solution is reduced from 450 to 100 bar at 26.5-degrees-C. Luminescence quenching results are consistent with a system of roughly spherical droplets, with size unaffected by the density of the continuous-phase solvent. However, the intermicellar exchange rate for the quencher is increased by a factor of 3 in the percolation regime. Only part of the increased exchange rate can be attributed to the decrease in the viscosity of the lower density propane, whereas the remainder is attributed to a clustering of the droplets resulting in more effective exchange. Lower propane density increases the strength of attractive interactions between the droplets, leading to extensive clustering and eventual electrical percolation. These results also confirm previous observations indicating that simply altering the strength of interdroplet interactions can induce electrical conductivity percolation. The observed behavior may be related to the early stages of a structural transition to a bicontinuous microemulsion that is believed to occur at higher volume fractions of the dispersed phase. These results also provide important new insights relevant to separation and reaction processes in near-critical microemulsion systems.