| In this dissertation we investigate theoretically the structure and the thermodynamic properties of linear and flexible polymeric brush adsorbed at the solid-fluid interface. A particular model system considered in this dissertation is the water-soluble poly-ethylen-oxide brushes (hereafter termed PEO brush) with hydrophobic groups at both ends, which is adsorbed at the polystyrene latex particle's surface. The main thrust of this work is first to develop a simple yet tractable theoretical model that may capture the essence of PEO brushes, and second, to make nontrivial predictions based on such a simple model, and search for experiments that may confirm our predictions. The starting point of our investigation is the observation made previously by several investigators that the key to peculiar properties exhibited by PEO in water, such as the anomalous temperature dependence of the second virial coefficient, is the formation of hydrogen bonds between water molecules and the PEO. We put such an observation into a rigorous mathematical form by introducing the density dependent excluded volume parameter in the free energy. We then employ the self-consistent field method advocated by Milner, Witten and Cates and make a nontrival prediction, independently reached by de Gennes and his collaborators, that PEO brushes form a very dense state near the interface if the free energy functional possesses a local minimum. Such a dense state occurs via a first order phase transition, with and without an attractive interaction between the interface and PEO backbone. Recent experimental observation by Kim and Cao (Euro. Phys. Lett., 24, 229 (1993)) of a dense state of PEO monolayers at the air-water interface appears to be a strong confirmation of the prediction of our model.;Next, we make an attempt to relate the phenomenological parameters introduced in our model system of PEO to experimentally measurable quantities such as enthalpy and temperature. By recognizing that the formation of the dense layer at the interface is caused by hydrogen bonding and could be characterized by the phase separation of PEO in water, we compare our free energy to one determined by Matsuyama and Tanaka (Phys. Rev. Lett., 65, 341 1990) to relate our phenomenological parameters to hydrogen bonding phenomena and demonstrate the possibility of the appearance of a local minimum in the free energy functional at room temperature.;Finally, we employ the fluctuating bond lattice model and present a Monte Carlo study of ordinary brushes that do not form hydrogen bonds with solvent molecules. We present simulation results for the density profile, end density profile, and force between the two walls attached by interacting polymeric brushes. Our results agree well with the predictions of self-consistent field theory. |
