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Block Sequence Directed Materials: Functional And Ordered Nanocomposites Derived From Block Copolymer Coassembly
Nanocomposite materials with ordered structures are critical for the advancement of numerous fields ranging from microelectronics to energy conversion and storage. However, there are few techniques for controlling the necessary nanoscale morphologies and compositions which are compatible with affordable, large-scale manufacturing. The coassembly of block copolymers with inorganic materials provides such a route to achieve controlled nanomaterials, but such examples have generally resulted in mesoporous single-component materials. In this thesis it is shown that the general challenge to achieve multifunctional nanocomposites directly from block copolymer coassembly may be surmounted by designing novel block copolymers where each block has the design intent to result in a functional component of the resulting nanocomposites. Such a method would enable block sequence directed materials (BSDM), where a sequence of three or more chemically unique polymer blocks direct the spatial arrangement and interface definitions of multiple functional materials. Towards this end, four examples are provided. First, a diblock copolymer poly(ethylene oxide-b-acrylonitrile) is demonstrated to enable direct synthesis of nanocomposites composed of crystalline titania and partially-graphitic carbon. Second, this method is expanded by adding a third chemically unique block to form PAN-b-PEO-b-PPO-b-PEO-b-PAN where now the use of three chemically distinct polymer blocks enabled control over each of the three final components: partiallygraphitic carbon, crystalline transition metal oxide, and porosity. Although these nanocomposites only possessed short-range order, tuning of the individual block lengths and block fractions resulted in control over the three components. Third, it is shown that highly-ordered, multi-ply nanocomposites can result from the coassembly of poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers. Tuning the ratio of nanoparticles to ISO enabled access to four unique morphologies and the selection of quasi-1D, 2D, or 3D pathways. Fourth, it is shown that an ordered 3D network morphology which is chiral (non-centrosymmetric) can result from the coassembly of an ISO with a particular composition. Such non-centrosymmetric nanostructures are necessary to enable macroscopic polarization for piezoelectric, pyroelectric, and second-order nonlinear optical properties in amorphous materials. Thus through these four examples, it is demonstrated that the tuning of the polymer-oxide coassembled systems enables control over both nanocomposite composition and morphology.
dissertation or thesis