Fabrication and Photochemical Surface Modification of Photoreactive Thin-Film Composite Membranes and Model Development for Thin Film Formation by Interfacial Polymerization

Abstract

<p>A simple route for the synthesis of a monomer containing a diazoketone functionality and two disulfonyl chloride groups has been developed. Polymerization of this monomer by reaction with a diamine leads to the formation of a polymer in which the photoreactive group is incorporated as a side chain. The polymer can be formed as a thin film in a thin-film composite membrane.</p> <p>The factors that affect the interfacial polymerization, membrane morphology and performance have been systematically investigated. It was found that monomer concentration, the presence or absence of a surfactant, solvent and polymerization time are important factors in determining membrane morphology and separation/flux performance.</p> <p>Small molecule model reactions have been studied in order to establish the chemistry of the photochemical surface modification of diazoketones. The range of photochemical transformations of diazoketones has been broadened, potentially leading to the photochemical conversion of the surface barrier layer of the diazoketone containing thin-film composite membranes to carboxylic acid, hydroxyl, ethyl ester and suIfur-containing crown ether.</p> <p>A method for the preparation of specimens for surface characterization of the thin-film composite membranes by infrared spectroscopy has been developed. Surface analysis techniques, such as Attenuated Total Reflectance Fourier Transform Infrared (ATR-FT-IR) Spectroscopy and Scanning Electron Microscopy (SEM), proved to be useful in monitoring the photochemical surface modifications of the photolabile thin-film composite membranes.</p> <p>The performance of the initial diazoketone precursor membrane and photochemically modified membranes has been examined with a series of aqueous solutions of inorganic salts. It was found that photochemical surface modification can significantly alter the separation/flux performance of the membranes.</p> <p>A theoretical model that considers both diffusion- and reaction-controlled interfacial polymerization, under nonsteady-state conditions, has been developed. The model can describe the formation of both dense and porous thin films. The results predicted by the model are consistent with experimental results. The general model developed in this thesis for thin film formation by interfacial polymerization can include the special model already reported in the literature. The work conducted in this thesis significantly extends existing theories for the formation of thin films by interfacial polymerization and provides an important guide for effective control of the thickness of the surface barrier layer of thin-film composite membranes prepared by interfacial polymerization.</p>