Microstructure, ion exchange, and transport in Langmuir-Blodgett ultrathin films
Abstract
Langmuir-Blodgett (LB) ultrathin films are highly ordered and organized organic materials. The goals of this dissertation are to understand fundamental physicochemical phenomena involved in the LB process; to characterize microstructures of ultrathin LB films; and to help develop engineering applications of thin films. Thermodynamic features of fatty acid Langmuir monolayers, at the air/water interface, interacting with dissolved metal ions were studied by introducing a new and simple electrochemical model. This model is useful for understanding conditions for stable Langmuir monolayers and for producing LB films of controlled ionic composition. Fourier transform infrared spectroscopy was then used for examining microstructures of deposited LB films. Novel methods of interpreting IR absorbances for polarized transmission and attenuated total reflection modes were developed to obtain quantitative information on the film microstructure. Various LB films of simple and complex molecules, including surfactants with single straight-chain, polymeric amphiphiles containing chromophoric side chain, and polymerized fatty acid surfactants with diacetylene chains, were investigated. The combined use of the above IR modes yielded detailed information about molecular orientations, both of specific groups and of molecular chains. The method is useful for studying microstructures of novel thin film materials for device purposes. The use of fatty acid ultrathin films as new ion exchange materials was also suggested. Fatty acid Langmuir monolayers showed a high selectivity over heavy metal ions such as cadmium or lead. Conditions for ion exchange breakthrough-type behavior were examined. Finally, certain transport properties of thin films were characterized by IR spectroscopy. Rigorous evaluation of water transport was made possible by developing new theoretical and experimental strategies. The results are important for testing the feasibility of using thin films produced by the LB or other processing methods, for membrane, barrier, and nonlinear optical applications.
Degree
Ph.D.
Advisors
Franses, Purdue University.
Subject Area
Chemical engineering
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