Formation and stability of emulsions produced by dilution of emulsifiable concentrates. Part II. The influence of surfactant concentration on the stability of oil-in-water emulsions

Abstract

The stability of oil-in-water emulsions has been investigated at 26°C as a function of surfactant concentration (Synperonic NPE 1800 + Ethoduomeen T20 in a 1:1 w/w ratio). From measurements of the change in the number of droplets and average droplet size with time, two surfactant concentration ranges could be distinguished. The first concentration range, where the stability of the emulsions increased with increase in surfactant concentration, was from 0–15% for homogenised emulsions and from 0–40% for unhomogenised emulsions. Above this concentration (in the second range) there was an apparent increase in the rate of coalescence with increase in surfactant concentration. The reduction in stability at high surfactant concentrations was postulated to be due to Ostwald ripening, which was enhanced by solubilisation of the oil molecules within the aqueous phase, thus enhancing their transport by diffusion as a result of the increase in concentration gradient in the presence of micelles.