New Procedure for Determining the Solubility of Lypophilic Nonionic Surfactants in Water

The procedure that allows to study the kinetics of a dissolution of oleophilic nonionic surfactants in water and to determine the equilibrium values of solubility (S ^eq _w) was proposed, based on the spectrophotometry of extremely dilute, finely dispersed o/w emulsions of these substances prepared by sonication. The equilibrium values of solubility of tetraethoxylated p-nonylphenol (Neonol AF_9-4) and sorbitan monolaurate (Span-20) at 293 K in water are 3.67 × 10^–5 and 1.03 × 10^–5 M, respectively. For the tetraethoxylated p-nonylphenol, the equilibrium value of solubility in water determined by the proposed procedure agrees well with that determined by precision tensiometric measurements.