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Morphological control in conjugated polymers : synthesis and applications of polymer microspheres Kelly, Timothy Lewis

Abstract

The synthesis, characterization, and application of conjugated polymer colloidal microspheres are reported. Monodisperse mesoporous silica spheres were utilized as hard templates for the preparation of poly(3,4-ethylenedioxythiophene) (PEDOT)–silica composites, which could in turn be etched with hydrofluoric acid to yield monodisperse conjugated polymer microparticles. The synthetic procedure was generalized to include other polymers such as polythiophene and poly(N-methylpyrrole). The colloidal and electronic properties of these composites were subsequently studied, and it was found that a balance between colloidal stability and electrical conductivity could be achieved when the mesopores of the silica template were partially filled with polymer. These insights enabled the successful self-assembly of an opaline film of the PEDOT–silica composite. Bragg diffraction of visible light by the lattice planes of the opal was then demonstrated. The silica host was subsequently explored for its ability to control the phase separation of polymer blends. It was found that depending on the order of polymer addition, phase separation could be suppressed. This resulted in an intimate mixture of the two constituent polymers, and has potential impact in the field of photovoltaics. The colloidal microspheres were also examined for their utility as electrode materials in supercapacitors. The PEDOT microspheres were found to have a mass specific capacitance higher than that of typical electropolymerized PEDOT films, indicating that the morphological control was translated into an improvement in device performance. An ion exchange and in situ polymerization approach was developed in order to incorporate poly(p-phenylenevinylene) into the mesoporous silica template. This yielded a luminescent colloidal material that displayed enhanced optical properties relative to the unencapsulated iii polymer. This is again due to the morphological constraints imposed on the polymer by the mesoporous template; polymer chains are isolated from each other, thus shutting down access to non-radiative decay pathways. Other template approaches were explored as a way of producing conjugated polymer microspheres. Sodium dodecyl sulfate micelles were utilized as soft templates for the synthesis of carbohydrate-functionalized poly(p-phenyleneethynylene) particles. These microparticles were examined for their protein-binding ability, and were found to extract the common lectin concanavalin A from solution.

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