Formation and stability of emulsions produced by dilution of emulsifiable concentrates. Part I. An investigation of the dispersion on dilution of emulsifiable concentrates containing cationic and non-ionic surfactants

Abstract

The ease of dispersion on dilution into water of emulsifiable concentrates (ECs) containing a nonionic surfactant (Synperonic NPE 1800) and a cationic surfactant (Ethoduomeen T20) has been assessed using the CIPAC test as well as from measurement of the average droplet diameter of the emulsions formed. A minimum of approximately 1% total surfactant was necessary to produce spontaneous emulsification, above which there was a gradual improvement in spontaneity and a reduction in average droplet size with increase in surfactant concentration up to 5%. With further increase in concentration, the average droplet size of the emulsions increased, although the spontaneity of emulsification was well maintained up to 20% surfactant. Further increase in surfactant concentration resulted in a deterioration in spontaneity, accompanied by further increase in droplet size, until with 40% total surfactant the dispersion of the oil became relatively poor. With 60% surfactant a very viscous EC was formed, which dispersed very slowly forming a “solubilised” system having a small average droplet size. The process of spontaneous emulsification was investigated using viscosity, density and interfacial tension measurements as well as from the phase diagrams for the ECs when diluted into water to various extents. Thermodynamic calculations showed that the interfacial tension was not lowered enough to cause spontaneous emulsification. The latter was attributed to interfacial turbulence caused by mass transfer of surfactant molecules from an EC across the oil—water interface and into the aqueous phase. The spontaneity decreased and the drop diameter increased in the range of surfactant concentration where the viscosity increased. This was taken as evidence of the rote of interfacial turbulence, which should be damped by the higher viscosity. The latter should also cause a reduction in diffusion of the surfactant molecules.