EXPERIMENTAL INVESTIGATIONS ON MODEL EMULSION SYSTEMS STABILIZED WITHNONIONIC SURFACTANT BLENDS

We have performed experimental research into model oil-in-water emulsi on systems stabilized with non-ionic surfactant blends: thin aqueous f ilms between oil phases and oil drops coalescing against their homopha se. Xylene was chosen as the oil phase, and Tween 20 and Span 20, alon e or in mixtures at different molar ratios, were used as stabilizers. The roles of the surfactant mole ratio, the electrolyte concentration and pH were studied. It was shown that there is considerable electrost atic repulsion within the aqueous films. The results obtained on thin film stability and on drop lifetime at constant electrolyte concentrat ion indicate that Tween 20 (when present) is the emulsifier that predo minantly determines the stability of the systems. This conclusion can be related to the higher surface activity and higher adsorption of Twe en as deducted from interfacial tension data. Some evidence of synergi sm was observed only at an electrolyte concentration of 10(-3) M (NaCl ). We also carried out stability tests on shaken and homogenized batch emulsion systems and the results show good correlation with the data from the model investigations.