Ultrathin films of functional polyelectrolytes on flat surfaces and colloidal particles using the layer-by-layer deposition technique

Layer-by-layer (LbL) self-assembly techniques have been used to prepare ultrathin polymer films with controlled thicknesses and compositions. The technique is based on the alternate adsorption of oppositely charged polyelectrolyte layers on substrates. This dissertation details the investigation of ultrathin films with functional polyelectrolytes coated on flat substrates and colloidal particles. Several systems were investigated including: liquid crystal (LC) photoalignment layers, photo-crosslinkable permselective membranes, luminescent hollow-shell particles, and conducting polymer colloidal particles. The multilayer films of an azo-polymer and a polycation were utilized to control azimuthal alignment of liquid crystals. Irradiation of a hybrid LC cell with linearly polarized light resulted in in-plane homogeneous LC alignment, which is dependent on the thickness, and irradiation time. The director of the LC molecules was found to be perpendicular to the polarization plane and can be reoriented. The photocross-linkable multilayer membranes comprising poly(acrylic acid) and poly(allyamine hydrochloride) modified with benzophenone groups have been prepared. It was demonstrated that the permeability of the multilayer films can be controlled by the number of layers as well as the UV irradiation time. Furthermore, a “smart” pH-switchable membrane was produced by adjusting the pH of the dipping solution while maintaining stability throughout the cross-linked structure. The membrane showed pH-sensitive permselectivity, that is, the film was permeable to the cationic molecules, but impermeable to the anionic molecules at pH 10 and vise versa at pH 3. Luminescent core-shell particles and hollow capsules were prepared by the LbL deposition of polystyrenesulfonate (PSS) and a water-soluble ionene precursor polymer containing fluorene units (PI) onto spherical colloid particles. Subsequent cross-linking of the PI in the multilayer shell formed luminescent conjugated oligo-fluorenes. Conductive core-shell particles were prepared by the deposition of polyaniline (PANI) and PSS multilayers onto polystyrene (PS) colloidal particles. PSS was used as a polymeric counter-ion for multilayer formation as well as a stabilizer and codopant for PANI. It was found that the PSS/PANI-coated particle is oxidatively more stable due to stabilization of the partially oxidized emeraldine salt by PSS. This dissertation describes unique approaches towards the science of materials design, synthesis and fabrication strategies, ultrathin film and colloid characterization, and development of potential applications.