Evaporation of aqueous dispersed systems and concentrated emulsions formulated with non-ionic surfactants

Vacuum evaporation of aqueous surfactant systems and concentrated oil-in-water (O/W) and water-in-oil (W/O) emulsions was studied as a function of the base oil (castor oil, heavy mineral oil and light mineral oil), and the kind of non-ionic surfactant (Tween and Span series) used in their formulation. Water evaporation rates were measured from aqueous surfactant solutions/dispersions (5% w/w surfactant), and O/W emulsions (5% w/w surfactant) in 1:1 water/oil weight ratio. Vacuum evaporation of W/O emulsions was also investigated, since a W/O emulsion is formed when the emulsion inversion point is surpassed during the evaporation of O/W emulsions. Surface tension, conductivity and particle/droplet size distribution were measured to characterize the formulated systems. Three simple models were tested to fit the evaporation rate data and their consistency depends on the system under consideration.