COULTER-COUNTER BASED COALESCENCE ASSAY FOR THE DETERMINATION OF EMULSION STABILITY AFTER ADDITION OF ELECTROLYTE

The coalescence assay of emulsions by UV absorbance measurements is distorted by the size-dependent scattering profiles of the droplets. After an initial increase, a plateau phase or even a decrease in absorbance can occur depending on the incubation time and coalescence velocity Minor coalescence cannot be detected A Coulter counter was employed to establish an assay based on the increase in the total volume of coalesced particles. The assay avoids the size-dependent distortions of the absorbance assay and proved to be more sensitive. The emulsion stability was studied as a function of CaCl2 concentration (250 mmol). The differences in the observed coalescence velocities correlated with the zeta potentials of the emulsions. Favourable proved the application of hemispherical electrodes (Delsa zetameter). This allowed zeta potential measurements in low and high conductivity liquids using the same capillary therefore excluding effects due to capillary change.