OSCILLATING PHASE-SEPARATION IN MICROEMULSIONS .1. EXPERIMENTAL-OBSERVATION

We examine the phase separation of a single phase of water-in-oil micr oemulsion droplets towards a phase of smaller water droplets coexistin g with a water-rich excess phase. This transition is found to oscillat e when induced by a continuous temperature increase. A periodic cloudi ng and clearing is observed under the microscope and in the microcalor imeter, allowing to determine the oscillation period from the extincti on of transmitted light and from the specific heat. The period depends on the surfactant concentration and increases as a square root of the scan speed. To the authors' knowledge this is the first time that osc illations in a temperature induced phase separation of a mixture have been observed. (C) 1997 American Institute of Physics.