5.5 HYDRODYNAMIC INTERACTIONS IN DISPERSIONS 106 5.5.1 Basic Equations. Lubrication Approximation 5.5.2 Interaction Between Particles of Tangentially Immobile Surfaces 5.5.2.1 Taylor and Reynolds Equations, and Influence of the Particle Shape 5.5.2.2 Interactions Among Non-Deformable Particles at Large Distances 5.5.2.3 Stages of Thinning of a Liquid Film 5.5.2.4 Dependence of Emulsion Stability on the Droplet Size 5.5.3 Effect of Surface Mobility 5.5.3.1 Diffusive and Convective Fluxes at an Interface; Marangoni Effect 5.5.3.2 Fluid Particles and Films of Tangentially Mobile Surfaces 5.5.3.3 Bancroft Rule for Emulsions 5.5.3.4 Demulsification and Defoaming 5.5.4 Interactions in Non-Preequilibrated Emulsions 5.5.4.1 Surfactant Transfer from Continuous to Disperse Phase (Cyclic Dimpling) 5.5.4.2 Surfactant Transfer form Disperse to Continuous Phase (Osmotic Swelling) 5.5.4.3 Equilibration of Two Droplets Across a Thin Film 5.5.5 Hydrodynamic Interaction of a Particle with an Interface 5.5.5.1 Particle of Immobile Surface Interacting with a Solid Wall 5.5.5.2 Fluid Particles of Mobile Surfaces 5.5.6 Bulk Rheology of Dispersions

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Chemical Physics of Colloid Systems and Interfaces

A mass transfer model for the extraction of weak acids/based in emulsion liquid-membrane systems

A theoretical model of oil solubilization in micellar surfactant solutions is developed. We consider oils that are practically insoluble in pure water, like triolein and other triglycerides. The nonionic micelles, which are capable to solubilize such oils, are usually rodlike aggregates, composed of surfactant molecules and poly(oxyethylene)-poly(oxypropylene) triblock copolymers, like Synperonic L61 (SL61). The swollen micelles, formed after solubilization, are smaller than the empty ones. The model describes the elementary act of solubilization as a sequence of three steps: (a) adsorption of an empty micelle at the oil-water interface; (b) uptake of oil by the adsorbed empty micelle which then splits into several swollen micelles; (c) desorption of the swollen micelles. Theoretical expressions are derived, which describe the diminishing of an oil drop in the course of solubilization. The parameter values, determined from the best fit of experimental data, imply that the rate-controlling step is the step of micellar adsorption. From the determined rate constant of adsorption we estimate the respective kinetic barrier to micelle adsorption, taking into account the action of surface forces and the hydrodynamic resistance. Our analysis indicates that the triblock copolymer SL61 promotes the solubilization of triglycerides by decreasing the length of the mixed surfactant-copolymer rodlike micelles, which leads to a lowering of the kinetic barrier to their adsorption at the oil-water interface.

/pdf/kinetics-of-triglyceride-solubilization-by-micellar-3ebuncie3d.pdf

Kinetics of Triglyceride Solubilization by Micellar Solutions of Nonionic Surfactant and Triblock Copolymer. 2. Theoretical Model

Dissolution of calcium salt of a long chain fatty acid or soap scum is a major challenge for hard surface cleaners since soap scum forms when soap is exposed to hard water and has very low water solubility. In this paper, the aqueous equilibrium solubility of calcium octadecanoate (or calcium stearate) was measured as a function of pH as well as chelating agent (ethylenediaminetetraacetate disodium salt) and surfactant concentrations. Anionic, nonionic, and amphoteric surfactants were studied. The highest soap scum solubility was observed at high pH with an amphoteric surfactant. Under this condition, the chelant effectively binds calcium, and the stearate anion forms mixed micelles well with the amphoteric surfactant, which is in zwitterionic form at high pH.

https://link.springer.com/content/pdf/10.1007%2Fs11743-010-1209-4.pdf

Dissolution Study of Salt of Long Chain Fatty Acids (Soap Scum) in Surfactant Solutions. Part II: Kinetics of Dissolution

Models for strongly exothermic absorption and reaction in falling films

The solubilization dynamics of oleic acid by aqueous sodium taurodeoxycholate solutions at 37°C does not conform to previous resistance in series models involving diffusion and interfacial steps. This is especially true as the ionic strength of the aqueous solution is increased by adding NaCl or by increasing the taurodeoxycholate concentration above 2%. Experiments conducted with a liquid/liquid stirred cell show that as the ionic strength is increased, the flux of oleic acid into the aqueous solution exceeds a reasonable value for the diffusion limit, assuming that oleic acid diffuses only in mixed micelles, and that the flux becomes independent of flow at these high ionic strengths. Two alternative models for the solubilization process are proposed. One involves a rapid exchange of oleic acid between mixed micelles and oleic acid free micelles in parallel with mixed micelle diffusion; and the second involves formation of a small emulsion droplet at the interface, which contains significantly more oleic acid than a mixed micelle, and which rapidly dissolves into micellar solution as the droplet leaves the interface.

Liquid solubilization dynamics: Oleic acid in bile salt

The hydrodynamics and mass transfer characteristics of a stirred cell for contacting immiscible phases are examined. When each phase is stirred with a rotating disk in laminar flow, such that the interface is stationary, the rate of diffusion in the absence of any interfacial resistance is obtained using a similarity solution. The hydrodynamics, specifically the radial velocity derivative at the interface, which is the most important component of the mass transfer solution, is obtained by combining the solutions for a finite disk and for the relationship between disk velocity and fluid core velocity. Excellent experimental agreement, within 5% of the theory, is observed.

Lawrence R. Stowe

Papers

Liquid solubilization dynamics: Oleic acid in bile salt

Hydrodynamics and mass transfer characteristics of a liquid/liquid stirred cell

Mass transfer with heterogeneous and first order homogeneous reaction using the film theory