In many experiments, surfactant adsorption and desorption at solid-liquid interfaces is found to be quite slow, considering that surfactants are small molecules. Attenuated total reflectance Fourier transform infrared spectroscopy was used to study the adsorption, desorption, and exchange of tetradecyltrimethylammonium bromide (C<sub>14</sub>TABr) at the silicon oxide surface. The exchange of surfactant was monitored using protonated and perdeuterated C<sub>14</sub>TABr. The data show that exchange of C<sub>14</sub>TABr between the surface and the bulk solution is very fast, complete exchange occurs in less than 10 seconds. A simple exchange model suggests that the disassociation rate constant of a single monomer is no less than 1 s<sup>-1</sup>, which is ~ 10<sup>4</sup> times slower than monomer exchange in bulk solutions. The actual exchange rate may be greater than observed in the present work due to transport phenomena. The rates of exchange are similar at concentrations above and below the critical micellar concentration. Adsorption is similarly rapid, but under some circumstances there is a small residue of surfactant that is slow to desorb. Desorption experiments utilizing KBr solutions of high and low ionic strength show that two thirds of each adsorbed micelle is held by hydrophobic association, and the other third is electrostatically bound. Adsorption, desorption, and exchange experiments at temperatures of 11°C above and 8°C below the Krafft temperature (14.4°C) show similar kinetics. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/34116 |
| Date | 19 August 2003 |
| Creators | Clark, Spencer C. |
| Contributors | Chemistry, Ducker, William A., Esker, Alan R., Anderson, Mark R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | Spencer_Clark_Thesis.pdf, Spencer_Clark_Vita.pdf |
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