I. Self-Assembly of Thioether-Modified Cationic Surfactants II. Electrostatic Binding among Equilibrating 2-D and 3-D Self-Assemblies 公开

Shi, Lei (2009)

Permanent URL: https://etd.library.emory.edu/concern/etds/ms35t868n?locale=zh
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Abstract

I. Self-Assembly of Thioether-Modified Cationic Surfactants

Cationic surfactants with one or two sulfur atoms inserted at various locations along their alkyl chains, were synthesized. Their colloidal properties were thoroughly explored by surface tension, fluorescence, and NMR. Furthermore, the thio-surfactants were adsorbed into sodium dodecyl sulfate micelles. An oxidant, periodate, was added to the system, and the subsequent rate of thioether oxidation to sulfoxide, determined by in-situ NMR, was found to be diminished (more or less equally for all sulfur loci) by two orders of magnitude. In contrast, rates of hydrogen peroxide oxidation were hardly perturbed by micellization. Once again, however, there was no rate dependence on sulfur location within the chains. These results are interpreted in terms of a disordered micelle in which all chain positions have roughly equivalent access to the micelle surface. The kinetic method for assessing exposure to the external medium is applicable to self-assemblies and polymer systems wherever the NMR resolution so permits.


II. Electrostatic Binding among Equilibrating 2-D and 3-D Self-Assemblies

Six organic additives bearing a different number of anionic charges, were added to a large excess of cationic surfactant (dodecyltrimethylammonium bromide, DTAB). The surface-tension vs. log [DTAB] plot for solutions containing DTAB/trianion = 15:1 showed an abrupt break (routinely taken as the critical micelle concentration, CMC) at 2.9 mM. This constitutes a 5-fold decrease compared with a CMC of 15 mM for pure aqueous DTAB. There is a 10-fold decrease in the break-point concentration caused by a mere 3.3 mol-% of hexanion. Corresponding CMC values from DTAB/trianion mixtures, measured by both conductivity and diffusion-NMR, gave normal values of 14 mM. The unusual discrepancy between the CMC based on surface tension and on the two "bulk" methods was attributed to saturation of the air/water interface by a DTAB/trianion complex far below the concentration at which the micelles form. Thus, the sharp break seen in surface-tension "CMC plots" need not in fact attest to actual micelle formation as is almost universally assumed in colloid chemistry.

Table of Contents

Table of Contents

I. Self-Assembly of Thioether-Modified Cationic Surfactants………………………1
Introduction………………………2

Surfactant and Self-Assembly………………………2

Surfactant Modification………………………6
Thioether………………………10
Synthesis………………………14
Results and Discussions………………………18
Surface Tension………………………18
Fluorescence Spectroscopy………………………31
NMR………………………43
Micellar Structure………………………56
Conclusions………………………62
Experiments………………………63
Materials………………………63
Methods………………………63
Syntheses and Purification………………………70
References………………………76


II. Electrostatic Binding among Equilibrating 2-D and 3-D Self-Assemblies………………………86
Introduction………………………87
Synthesis………………………93
Results and Discussions………………………98
Surface Tension and Conductivity………………………98
UV-Vis Spectroscopy………………………116
PGSE-NMR………………………119
Conclusions………………………126
Experiments………………………127
Materials………………………127
Methods………………………127
Syntheses and Purification………………………130
References………………………133

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