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. (C) 2013 Elsevier Ltd. All rights reserved.