Coulter coalescence measurement

Provided that the emulsion does not undergo any flocculation, the coalescence rate can be measured simply by following the number of droplets or average diameter as a function of time. For this, a given volume of the emulsion is carefully diluted into the Isotone solution of the Coulter counter, and the number of droplets is measured. The average diameter can be obtained using laser diffraction methods (e.g., with the Master Sizer). By following this procedure at various time periods, the coalescence rate constant K can be obtained. 

The rate of coalescence of the droplets in a macroemulsion is stated to be the only quantitative measure of its stability (Boyd, 1972). It can be measured by counting the number of droplets per unit volume of the emulsion as a function of time in a haemocytometer cell under a microscope (Sherman, 1968) or by means of a Coulter centrifugal photosedimentometer (Groves, 1964 Freshwater, 1966). 

For quantitative assessment of emulsion stability after dilution of the EC, it is necessary to measure the coalescence rate. This could be done by measuring the droplet number as a function of time, using, for example, a Coulter counter. As an illustration, Figure 14.5 shows the results obtained using the model xylene EC. 

The break-up of Newtonian liquids with various viscosities t] can be investigated by mastication of small oil samples and measuring the resulting droplet size distribution, using a Coulter Counter or a Master sizer. Samples are expectorated into a suitable surfactant solution, e.g. Tween (to prevent coalescence during measurements). can be measured at 37 °C (body temperature) using a suitable rheome-... 

---