BLOCK COPOLYMER DERIVED FUNCTIONAL NANOMATERIALS WITH THREE DIMENSIONAL POROUS STRUCTURES FOR PHOTONICS AND WATER APPLICATION
Block copolymer (BCP) self-assembly provides a convenient approach to access nanostructures at the tens of nanometer scale. Porous scaffolds from block copolymer self-assembled morphologies have a plethora of applications in areas including energy, filtration, and photonic devices. Selectively etching methods to remove one block are typically used to achieve porous structures derived from BCP equilibrium morphologies. BCP directed additive co-assembly, facilitated by thermal or solvent-vapor annealing processes and followed by BCP removal, is also routinely employed to achieve porous structures composed of non-BCP materials. In the first part of this thesis, fabrication and characterization of three dimensional (3D) gyroidal mesoporous thin films are discussed made from BCP-resin/carbon composites. Spin-coated films made from triblock terpolymer plus pre-carbon precursors were subjected to solvent vapor annealing (SVA) to reach the desired gyroidal equilibrium morphology. In situ grazing incidence small angle x-ray scattering (GISAXS) was employed to elucidate structure evolution at different swelling stages during SVA and to identify appropriate conditions to quench films into the gyroid structure at room temperature. After crosslinking of carbon precursors and thermal decomposition of the BCP, a carbon scaffold with gyroid morphology was formed. Such 3D gyroidal thin films have multiple advantages over conventional templates. They have high temperature resistance up to 900 °C under non-oxidizing conditions, which makes them compatible with deposition processes such as chemical vapor deposition. 3D pore size and hydrophilicity are tunable, facilitating the deposition of different types of materials into the nano-scale pores. Finally, a transfer technique for such gyroidal mesoporous thin films was developed to eliminate restrictions of film formation to specific substrates. These gyroidal carbon mesoporous thin film templates largely expand the materials selection pool for gyroidal structures. BCPs not only provide 3D scaffolds from equilibrium morphologies, but also can form 3D hierarchical superstructures with graded meso- to macro-scale pores from non-equilibrium processes. Resulting membranes have uniform surface mesopores supported by a graded macroporous sublayer. The process to generate such asymmetric ultrafiltration membranes is termed self-assembly plus non-solvent induced phase separation, or simply SNIPS. SNIPS membrane performance is largely controlled by details of the meso- and macro-porous structures. In the second part of this thesis, BCP derived SNIPS membrane ultrafiltration performance with respect to flux and solute diffusion rates is studied in relation to surface mesoporous and sublayer macroporous structures. These structures are systematically tuned identifying several key factors in the membrane casting process. To explore SNIPS membrane pore surface functionality, a new BCP membranes was designed and synthesized with thiol functional groups exposed on pore walls and membrane surfaces. A series of experiments were conducted to illustrate the accessibility of these functional groups after membrane fabrication. Conjugation reactions between maleimide functionalized dye and thiol membrane demonstrated that the thiol functional groups were active as covalent binding sites when simply soaking the membranes into target molecule solutions. We expect these functional membranes to enable biosensing and multi-level responsive smart materials applications.
Block copolymer self-assembly; Functional nanomaterials; Materials Science; 3D structure
Wiesner, Ulrich B.
Ober, Christopher Kemper; Thompson, Michael Olgar
Materials Science and Engineering
Ph. D., Materials Science and Engineering
Doctor of Philosophy
dissertation or thesis