Kinetics of Triglyceride Solubilization by Micellar Solutions of Nonionic Surfactant and Triblock Copolymer. 1. Empty and Swollen Micelles

Abstract

By NMR and static and dynamic light scattering we investigated how the micelle size, shape, and aggregation number vary during the solubilization of triolein in mixed aqueous solutions of the nonionic surfactant C12En (n ) 5 or 6) and the nonionic triblock copolymer Synperonic L61 (SL61). The latter was found to strongly accelerate the solubilization, although the copolymer alone is unable to solubilize triglycerides. A series of solutions containing different concentrations of surfactant and copolymer has been studied. The light scattering shows that we are dealing with giant micellar aggregates, each of them containing hundreds to thousands of surfactant molecules and dozens of copolymer molecules. Assuming that the micelles have the shape of prolate ellipsoids, we calculated their length and width. The results indicate that the initial, strongly elongated micelles transform into spherical or slightly ellipsoidal ones at the end of solubilization. The micelle aggregation number and hydrodynamic radius decrease by factors of 2-6 during the solubilization; i.e., one empty micelle splits into several smaller swollen micelles of radius 4-5 nm. The NMR measurements reveal that the equilibrium solubilization capacity (solubilized oil/mol of surfactant) is virtually not affected by the addition of SL61. Hence, the copolymer accelerates the process without influencing its final result; that is, SL61 acts as a promoter of solubilization. The results are used in the subsequent two papers of this series to develop a kinetic model of triglyceride solubilization and to verify it against experimental data.

Formulation of ultralow interfacial tension systems using extended surfactants

“…This is consistent with the extremely low solubilization parameters reported for these systems (17).…”

Solubilization rates of oils in surfactant solutions and their relationship to mass transport in emulsions

“…Electrical repulsion between micelles and drop greatly reduces the likelihood of collision between them or even close approach. A recent demonstration of this effect with triolein, where mechanisms involving molecular dissolution could be ruled out, was provided by Kralchevsky et al [11,38,39].…”

“…Kinetic studies aim at determining the limiting step(s) within such mechanisms that dictate mass transfer rates and transient behavior. Most kinetic studies have been interpreted in terms of the same basic mechanisms as discussed above for individual drops: (a) the diffusion of the transferred solutes in the bulk as individual molecules [28,48] or incorporated in micellar aggregates [26,29]; (b) the interfacial resistance to mass transfer, which may refer to transport across a surfactant monolayer or some other physical barrier when molecular dissolution prevails [30][31][32] or to the adsorption and emission of micelles that act as carriers for the transported compounds [1][2][3][4][5]7,8,11,38,39,49]; or (c) the molecular diffusion of the solute in the continuous phase and subsequent capturing by surfactant micelles [10,18]. Recent advances in the understanding of the role of solubilization kinetics on the emulsion destabilization mechanisms as described above are discussed below.…”

Formulation and Characterization of Phytophenol-Carrying Antimicrobial Microemulsions

“…The solubility of hydrophobic compounds in microemulsions can be many magnitudes higher than the solubility of the compounds in the polar solvent in the absence of surfactant micelles. [9][10][11][12] The process by which the non-polar molecules, in this case essential oil components, are incorporated into the surfactant aggregates is referred to as solubilization. 13 Microemulsions are thermodynamically stable systems unlike conventional colloidal dispersions such as emulsions or suspensions.…”