Formation and stability of miniemulsions produced by dispersion of water/oil/surfactants concentrates in a large amount of water
Résumé
Phase diagrams of the pseudo-ternary (water, NaCl)/(paraffininc oil or tetradecane)/(TTAB, N-tallow amine) systems have been determined. Some of these systems, so-called concentrates, have been dispersed in water, at the concentrate to water weight ratio of 5/95. We have investigated the effect of composition variables and parameters of dispersion on the quality (mean size, standard deviation) of the miniemulsions formed. The droplet size distribution of the miniemulsions has been determined by using dynamic light scattering of samples submitted to further dilution. According to the dynamic light scattering results the composition, surfactant concentration, location in the phase diagram and temperature of the concentrate, and also the salinity and temperature of the water used for dispersion have an effect on the quality of the miniemulsions formed. However, this quality increases (smaller droplets and narrower droplet size distribution) when both the composition of concentrate favours the flexibility of the surfactant film and the physico-chemical conditions of the water used for dispersion increases the affinity of the surfactant film for water, and then favours the spontaneous emulsification of the concentrate. Ostwald ripening was responsible for the destabilisation of the miniemulsions.