Kinetics of Solubilization of n-Decane and Benzene by Micellar Solutions of Sodium Dodecyl Sulfate

• Published in: Journal of colloid and interface science Vol. 245; no. 2; pp. 371 - 382
• Main Authors: Todorov, P.D., Kralchevsky, P.A., Denkov, N.D., Broze, G., Mehreteab, A.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 15-01-2002; Elsevier
• Subjects: benzene; Chemistry; Exact sciences and technology; General and physical chemistry; n-decane; sodium dodecyl sulfate; solubility of oil in water; solubilization kinetics; Surface physical chemistry; Surface-active agents: properties; surfactant micelles; n-decane; sodium dodecyl sulfate; solubility of oil in water; surfactant micelles; benzene; solubilization kinetics; Anionic surfactant; Decane; Hydrocarbon; Benzene; Alkane; Sodium compound; Kinetic parameter; Experimental study; Solubilization; Micellar solution; Lauryl sulfate
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.2001.8031

We observed the diminishing of single microscopic oil drops to study the kinetics of solubilization of n-decane and benzene by micellar solutions of sodium dodecyl sulfate (SDS). Each drop is located in a horizontal glass capillary of inner diameter 0.06 cm filled with a thermostated surfactant solution; the small vertical dimension of the cell prevents the appearance of uncontrollable thermal convections. The experiments show that the radius of an n-decane drop decreases linearly with time, whereas for benzene this dependence is nonlinear. To interpret the data, a kinetic model of solubilization is developed. It accounts for the diffusion and capturing of dissolved oil molecules by the surfactant micelles, as well as for the finite rate of oil dissolution at the oil-water interface. By processing the data, we determined the rate constant of solubilization for a given oil and surfactant. It turns out that the elementary act of catching a dissolved oil molecule by a surfactant micelle occurs under a barrier (rather than diffusion) control. The effective rate of solubilization is greater for the oil, which exhibits a higher equilibrium solubility in pure water (benzene), despite the lower value of the solubilization rate constant for this oil.