Transport in Complex Self-assembled Surfactant Systems PDF Download

Author: Wyatt Jacob Musnicki
Publisher:
ISBN: 9781267969217
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Languages : en
Pages :

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Book Description
The purpose of this work is to advance the understanding of the diffusive transport of hydrophobic compounds (pharmaceuticals, nutraceuticals, flavors, pesticides, etc.) solubilized in microemulsions and the particles that carry them through solution and in fibrous media. The first focus of this research was to investigate the gradient-diffusion of charged anionic micelles in solution and a fibrous gel at moderate but dilute concentrations above the critical micelle concentration. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used extensively to measure the micelle gradient-diffusion coefficient as a function of surfactant concentration at multiple sodium chloride and gel concentrations. The micelle diffusivity was shown to increase linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle-micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement, particularly at the higher salt concentrations. The second focus of this work was to investigate the gradient-diffusion of hydrophobic compounds in microemulsions. Three solutes of increasing hydrophobicity were used and two different types of surfactants, one non-ionic and the other anionic, were investigated. The transport of the hydrophobic compounds within the microemulsions were tracked using holographic interferometry. For three of the solute-surfactant pairs, the measured interferometry patterns exhibited pseudo-binary features and the effective binary diffusion coefficient of the solutes was extracted from these patterns. The effective diffusion coefficient of one solute-surfactant pair was between the slowest diffusing component, the micelle, and the fastest diffusing component, the solute in water. The other measured effective diffusivities were either much smaller than the micelle diffusivity or much larger than the solute's diffusivity in water. For the remaining three solute-surfactant pairs, the interferometric patterns clearly demonstrated the transport of more than two components. For these, the effective binary diffusion coefficients could not be extracted. To improve on the pseudo-binary results and to account for the coupled transport of solute, a ternary multicomponent method was adapted for use with holographic interferometry. The ternary diffusivities: D11, D12, D21, and D22 were determined for all sets of solutes and surfactants. The value of D22 were found to be in all cases equal to the micelle diffusivity. The values of D11 were found to be less than the solute's diffusivity in water and to decrease as the solute's hydrophobicity increased. The values of D12 and D21 were found to depend in a complex manner with the solute's hydrophobicity and the type of surfactant used. Holographic interferometry was a useful tool for extracting complex information from the transport mechanisms of the solute and surfactant gradient-diffusion in micelles and microemulsions.