Nanostructured conducting materials prepared from block copolymer templates.

摘要

Interest in nanostructured conducting materials, such as graphitic carbon and conjugated conducting polymers, has blossomed in recent decades, with such materials finding applications as components in sensors, field effect transistors, supercapacitors, fuel cells, lithium ion batteries, PLEDs, and others. Various methods of structural control have been used to initiate the formation of such nanostructures, including hard and soft templating methods. Soft templating methods using surfactants, block copolymer micelles, or self-assembled block copolymer thin films produce materials that do not require template removal, and the template itself may function to improve or preserve physical properties in the resultant materials.;The author of this thesis has developed several methods of soft templating for the preparation of conducting nanostructured materials. Block copolymers containing both a low Tg hydrophobic segment (n-butyl, ethyl, or methyl acrylate) and an acidic segment based on 2-acrylamido-2-methyl-N-propanesulfonic acid (AMPSA) were prepared by controlled radical polymerization. These methods including reversible addition-fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP), and the prepared copolymers included diblock copolymers, triblock copolymers, and molecular brushes. These block copolymers were then used as templates for conducting polymers containing a nitrogen heteroatom, such as polyaniline (PANI) and polypyrrole (PPY), with the acidic AMPSA block functioning as the dopant for the conducting polymer. After deprotonation, the acid groups also function as complexing counterion to the positive charges induced along the conjugated backbone. Both thin films of nanostructured PANI and discrete conducting nano-objects of PANI and PPY templated on triblock copolymer micelles were prepared by these methods. Characterization of the nanostructures by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) were undertaken, while electronic properties were primarily characterized by the four-point probe method and UV-Vis spectroscopy.;Similar templating methods were used for the preparation of nanostructured carbon materials. In these cases the templates were block copolymers containing a carbon precursor such as polyacrylonitrile (PAN) or polyvinylacetylene (PVA) and a sacrificial block that decomposed at high temperature such as n-butyl acrylate (BA) or methyl methacrylate (MMA). PAN-containing block copolymers were characterized by grazing-incidence small angle X-ray scattering (GISAXS), AFM, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) prior to pyrolysis and carbonization, while the nanostructured carbons were characterized by Raman spectroscopy, GISAXS, AFM, UV-Vis, and matrix-assisted laser desorption/ionization (MALDI/LDI). Additionally, the potential for crosslinking low molecular weight PAN-b-PBA in order to prevent rearrangement and loss of nanostructures at elevated temperatures was also investigated, through the addition of free crosslinkers as well as the incorporation of various crosslinking moieties into the polymer backbone. The resultant films where characterized by AFM before and after UV irradiation.;While PAN polymerization and block copolymerization by ATRP has already been extensively covered in the literature, the polymerization of PVA by such methods, as well as the subsequent preparation of block copolymers, has not been studied prior to the work contained in this thesis. ATRP of TMS-protected PVA (PVATMS) was optimized, and a range of sacrificial polymers, including both acrylates and methacrylates, were used as macroinitiators for chain extension with PVATMS. The subsequent polymers were characterized by AFM, GISAXS, 1H-NMR, Fourier transform infrared spectroscopy (FTIR), TGA, and DSC, both before and after deprotection of the acetylene groups, a prerequisite for efficient carbonization of the PVA. Based on poor phase separation after deprotection, the possibility of grafting PVA from silica particles was explored as a method of preparing porous nitrogen-free nanocarbons via thermal deprotection of PVATMS. The possibility of incorporating a p-type dopant such as boron into PVA-based carbon was also investigated, using ATRP copolymerization of a boron-functionalized styrene and PVA and PAN. The % retention of the boron groups was approximated by TGA analysis. (Abstract shortened by UMI.)