ARTICLE:

• COALESCENCE AND EMULSION STABILITY IN LIQUID-LIQUID SYSTEMS  download article

T. M. Dreher
Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria, 3052, Australia

G. W. Stevens
Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria, 3052, Australia

ABSTRACT

Understanding the factors that influence the coalescence of single drops at an interface in liquid-liquid systems is an important precursor to understanding emulsion stablity and the behaviour of droplet swarms such as occurs in many liquid extraction pocesses. Three techniques have been used to examine the coalesncence process of single drops. Atomic force microscopy enables direct measurement of the fundamental forces at a liquid-liquid interface, scanning ellipsometry/interferometry is used to measure the film thickness profile during the drainage process, and single drop coalescence time measurement is used for quantitative comparative studies of effects of various emulsifiers.
Data is presented that shows the addition of large molecular weight polymers to the organic continuous phase increases signifciantly the coalescence time for small drops but has no effect on the coalesence time of large drops. This is explained in terms of the effect of the polymer on the rheology of the organic phase and the shear stress experienced by the fluid in the film between the drop and the free surface.

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