"This dissertation investigates the swelling and fouling resistance of polyanionic and polyzwitterionic brushes in the presence of surfactants and surfactant-stabilized oil-in-water (O/W) emulsions. Such emulsions are an undesired byproduct of many processes, the largest of which is the massive oil and gas extraction industry. Among the three existing forms of oil (free oil, dispersions and emulsions), emulsions are the most difficult to treat due to the small oil droplet size (< 20 æm) and surfactant-enhanced emulsion stability. Membrane filtration is an effective method for removing oil from emulsions, but fouling induces a rapid decline in permeate flux that may make such separations impractical. Polyelectrolyte brushes can potentially resist oil fouling because they are superoleophobic in aqueous solutions due to their strong water affinity. This research employs surface-initiated atom transfer radical polymerization for relatively controlled growth of polyanionic and polyzwitterionic films. Poly(3-sulfopropyl methacrylate potassium salt) (PSPMK) brushes formed on Au surfaces show underwater hexadecane contact angles of nearly 180°. Due to electrostatic repulsion, these polyanionic brushes do not adsorb the anionic surfactant sodium dodecyl sulfate (SDS). Moreover, with SDS-stabilized O/W emulsions, microfiltration membranes modified with PSPMK brushes show 1003030% oil rejection and a constant permeate flux, indicating minimal fouling during 12-h, dead-end filtrations. In contrast, electrostatic attraction causes strong adsorption of the cationic surfactant cetrimonium bromide (CTAB) to PSPMK brushes, and this leads to brush collapse and no oil rejection during filtration. Thus, polyanionic brushes effectively resist oil fouling, but only for emulsion stabilized with anionic surfactants. To investigate whether zwitterionic films can resist adsorption of both cationic and anionic surfactants, this work employed poly(sulfobetaine methacrylate) (PSBMA) brushes. Unfortunately, both cationic and anionic surfactants adsorb to these brushes, and swelling in surfactant solutions depends on surfactant charge and concentration, as well as brush thickness. Preliminary data show that during the filtration of O/W emulsions, the permeate flux is much lower than the pure water flux, presumably because of fouling. Moreover, the permeate flux increases during filtration, implying brush collapse after oil adsorption. Compared with the strong fouling resistance of anionic PSPMK brushes to negatively charged oil droplets, the nearly neutral zwitterionic brushes have little charge repulsion to oil droplets and show low resistance to fouling. During filtration with PSBMA-modified membranes, oil coalescence occurs. As an alternative approach to separate O/W emulsions, membrane coalescence traditionally employs hydrophobic membranes to prompt oil attachment and coalescence on the surface. Preliminary data show that superoleophobic membranes can also induce oil coalescence and are less fouled than traditional hydrophobic membranes."--Pages ii-iii.
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