Critical Electric Field Measurement

CEF is a measure of the electric field strength required to induce the flow of current through an emulsion and is the electric field at which the first signs of macroscopic conductivity are observed. All experiments are performed at room temperature.

To measure CEF, an emulsion sample is syringed into the sample cell consisting of two, 1.0 cm diameter, gold plated, copper electrodes, separated with Mylar spacers and held in an aluminum casing. The cell is connected to a HP6634B power supply (0-100 V dc source), controlled by a PC through the use of a HP82350A interface card. The power supply is controlled with a Visual Basic program. The gap width of the cell can be varied, but for most experiments it's set at 0.250 mm.

After the cell is loaded with the sample, the voltage between the electrodes is increased in increments of 0.25 V every 5 seconds, and the current is measured 2 seconds after every step change (to avoid current spikes). Due to sensitivity to droplet size, the emulsions are always taken from a location 1 cm below the free surface of the emulsion. Microscopic observations are performed in parallel with CEF measurements to verify valid sampling procedures.