Ph.D Thesis

Ph.D StudentSaar Kirmayer
SubjectThe Self-Organization Mechanism of Semiconducting Polymer/
Mesoperiodic Silica Nanocomposites
DepartmentDepartment of Materials Science and Engineering
Supervisor Full Professors Frey Gitti
Full Thesis textFull thesis text - English Version


Composite materials are designed to exploit beneficial properties of their individual components and to obtain desirable properties, which are distinct or unattainable from the separate constituent species. One promising class of nanocomposites is based on the incorporation of organic functional molecules into a mesoscopically ordered inorganic matrices. This offers prospects for property-adjustments according to interactions of the functional organic species with each other, with the organic structure-directing agents, and/or with the inorganic host. However, the aqueous conditions required for the deposition of mesostructured metal-oxides, from a combination of sol-gel chemistry and surfactant self-assembly, inhibits the incorporation of hydrophobic guests into the inorganic scaffold during its formation. Here, three synthetic approaches have been suggested to overcome this hydrophilic/hydrophobic incompatibility. In the first approach the solvents conventionally used for the deposition of mesostructured metal-oxides, ethanol and water are replaced by a solvent suitable also for hydrophobic molecules, tetrahydrofuran (THF). Under these conditions, the water molecules necessary to induce surfactant self-organization are controllably generated in-situ so they do not cause sedimentation of the hydrophobic guest. In a second approach, the conventional ethanol-water based sol-gel process is used while the hydrophobic and hydrophilic phases are compatibilized by surfactant-stabilized emulsions. Finally, judiciously synthesized surfactants, comprising a conjugated segment as the hydrophobic block, were used to template the metal-oxide framework from a conventional hydrophilic sol-gel solution. Scattering techniques were used to study the solution behavior of the different systems while transmission electron microscopy (TEM), small angle x-ray scattering (SAXS), x-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR) techniques were used to characterize the mesostructure of the composite materials. Absorption and emission measurements were used to study the environment and interactions of the incorporated species. All three methods enabled a successful incorporation of the conjugated guest molecules into the mesoscopically ordered inorganic matrix during its formation. The incorporated hydrophobic conjugated polymers, maintained their optical properties during and after incorporation into the oxide host, while exhibiting a better environmental stability. 

The model system used in this research, mesoperiodic silica as the host and conjugate polymers as the guest molecules, demonstrates a general approach, which can be further extended to allow the incorporation of functional organic hydrophobic guests into sol-gel synthesized metal-oxide frameworks during their formation.