| dc.description.abstract | ABSTRACT In recent years, the physical and chemical properties of hydrophilic surfaces been exploited in a number of novel applications. Especially, amphoteric membranes were the focus of many theoretical studies since they have a wide range of applications particularly in bio separation techniques. This particular study sought to determine surface characteristics of amphoteric and acidic membranes. Simple and reliable surface characterization method is important for understanding of membrane surface chemistry, separation performance and fouling resistance. Surface properties such as acid-base, hydrophilicity and hydrophobicity in which the performance of the polymer membranes is dependent on, were determined by contact angle using the immersion method. First, the surface properties of model commercial amphoteric membranes were characterized followed by lab-made amphoteric and acidic surfaces were investigated. A typical commercial amphoteric Blotting Nylon 6, 6, Type A membrane, plates of Polyoxymethylene modified by chromic acid as well as methyl acrylate based lab-made acidic and amphoteric membrane were examined. These new membranes were prepared using methyl methacrylate as monomer, di (ethylene glycol) diacrylate as cross linker, anionic methacrylic acid and cationic 2-(N, N-dimethyl amino) ethyl methacrylate as functional monomers. The syntheses were made by means of photo induced radical polymerization via camphorquinone/amine initiator. The contact angle titration curve for each membrane immersed in aqueous solution shows that the contact angle is sensitive to the degree of ionization of the surface functional groups. Moreover, surfactant adsorption property of the surfaces were determined using ceryl trimethylammonium bromide and sodium dodecyl benzene sulfonate (well below their critical micelle concentration) solutions as a function of pH. The contact angle titration curve in the presence of these surfactants describes the surface can go from hydrophilic to hydrophobic upon the adoption ionic surfactant depending on the pH, surface charge density and surfactant concentration. Furthermore, scanning electron microscopy (SEM) has been used to characterize surface morphology of the amphoteric and acidic surfaces. The SEM image of the commercial surface showed that, the surface has high porosity, rough, uneven, and the pore size and hydrophobicity increase upon the adsorption of ionic surfactant. However, polyethylene surface did not show any visible changes after treatment. In addition, SEM image of the synthesized amphoteric surface was also analyzed. From the results of this study, it can be concluded that the change in contact angle as a function pH is sensitive to the degree of ionization of surface functional groups. The adsorption of ionic surfactant is dependent on the membranes acidity, basicity and surfactant concentration as functions of pH. Besides, synthesis of membranes by photo polymerization of acrylate based monomers can be used for the preparation of functionalized surfaces. On top of that, based on the experiments done in this thesis, it can be concluded that the hydrophilicity, acidic and basic of surface groups can be determined using the immersed contact angle method. Therefore, it could be possible to suggest that determination of surface properties of anionic and/or basic surfaces using contact angle immersed method should be given emphasis for the development functionalized membranes. | eng |