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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Materials Chemistry | Other Physics | Polymer and Organic Materials | Polymer Chemistry
Functional hybrid materials, commonly comprising two distinct constituents at the molecular or interfacial level, have increasingly drawn significant interest for a broad range of applications in nanoelectronics to supercapacitive energy storage and bioengineering. However, common synthetic routes toward this class of materials often face a tradeoff among structure-property control, performance enhancement, procedural simplicity and scalability. This dissertation presents innovative fabrication platforms, zwitterist and freeze-burn, for simple fabrication of functional hybrid electronic and porous materials, respectively, by leveraging polymer chemistry, phase separation, and interfacial interactions.
Chapter 1 overviews recent prominent methods for preparing hybrid electronic and porous structures while describing their advantages and disadvantages. In particular, photolithography and rapid thermal annealing (RTA) are highlighted and motivate the conception of the molecular and process designs in the succeeding chapters.
Chapter 2 examines the influence of steric footprint on the work function modulation of graphene with sulfobetaine-based polymer zwitterions via dipole doping. Of the polymers studied, the piperidinyl-substituted version possessing the bulkiest steric group induced the largest work function reduction (n-type doping), as observed from spectroscopic measurements and theoretical calculations. Aside from the zwitterions, the functional polymers also consist of methyl methacrylate and photo-crosslinklable benzophenone units to enable patterning of “zwitterist” (a portmanteau word from zwitterion and photoresist) without requiring an additional component for photolithography. Spatial work function engineering of graphene by the patterned structures was revealed by Kelvin probe force microscopy. The zwitterist platform also permitted the production of a half-covered graphene field-effect device with a signature p-n homojunction curve.
Chapter 3 progresses the previous chapter by extending the zwitterist molecular design to a novel class of fluorinated polymer zwitterions, leading to the “fluorozwitterist” platform. This enabled the demonstration of p-type doping of graphene by zwitterionic polymers for the first time. The zwitterionic (choline phosphate) and fluorinated moieties exhibited a synergistic electronic action upon contact with graphene. By co-patterning fluorozwitterist and zwitterist, both local work function increase and decrease were measured on the same substrate relative to nearby bare graphene regions, resembling a p-i-n diode configuration.
Chapter 4 introduces “freeze-burn” as a simple top-down method for creating porous carbon networks by polymer-templated RTA (> 50 °C/sec). This technique activates sequential templating (freezing or holding a carbonaceous material within one domain of a phase-separated polymer blend) and degradation (burning of polymer template) in < 10 minutes. The model system is composed of particles of reduced graphene oxide mixed with a polystyrene/poly(vinyl methyl ether) blend possessing a lower critical solution temperature (LCST). The dependence of macropore formation on particle loading and annealing ramp rate was captured by glass transition temperature, which is indicative of polymer mobility. Without changing the template composition or processing conditions, the freeze-burn method also yielded templated network structures of graphene oxide, carbon black, carbon nanopowder, and carbon nanotubes.
Chapter 5 builds upon findings from the preceding chapter by utilizing an LCST-type polyacrylonitrile (PAN)-based random copolymer blend system for “freeze-burn 2.0” or bottom-up synthesis of porous heteroatom-doped carbon networks via RTA. In this case, structural freezing involves crosslinking of phase-separated PAN domains and dopant atom incorporation, while burning comprises degradation of porogens and elimination of non-carbon species as volatiles. It should be noted that the model polymer blend acts as both the template and the carbon source, thereby generating mechanically stable porous carbon films on a variety of substrates. The addition of a boron-containing compound in the precursor film enables incorporation of the heteroatom for enhancing the supercapacitance and wound healing activity of the fabricated hybrid material.
Pagaduan, James Nicolas, "Designer Functional Hybrid Materials: From Zwitterists to Freeze-Burn Method" (2023). Doctoral Dissertations. 2937.
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