Title

Organic-Inorganic Composite Materials: Molecular Tailoring of Structure-Property Relationships

Date of Award

1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Kenneth A. Mauritz

Advisor Department

Polymers and High Performance Materials

Abstract

Continuing the investigation of nanocomposite materials, Nafion ® perfluorosulfonate ionomers (PFSIs) are utilized as morphological templates in which the hydrophilic, nanometers-in-size clusters serve as preferred sites for in -situ , catalyzed, sol-gel reactions of silicon alkoxides. This research sought to create unique organic-inorganic nanocomposites. By changing the organic nature of the co-reactant and adjusting the ratio of TEOS to co-reactant in order to control the organic fraction, this research seeks to tailor a spectrum of micro-chemical environments within the Nafion ® template. Prior to structure-property analysis, a detailed structural evaluation utilizing FT-IR and 29 Si solid state NMR spectroscopy was performed. These molecular structure issues were essential because they have an effect on the actual properties of the Nafion® /ORMOSIL hybrids, such as mechanical tensile testing, fluorescence, and gas diffusion. Experiments were then conducted in order to determine how changing the organic nature of the co-reactant and adjusting the ratio of TEOS to co-reactant in order to control the organic fraction affected structure-property relationships. While definitive trends can be extracted from the mechanical data with respect to each individual organic moiety and quantity of the organic moiety, there does not appear to be any specific trends in the thermal transitions from the DMA data. Fluorescence studies determined that by changing the organic modifier molecule and the quantity of the modifier that the hydrophobicity and polarity of the internal environment of the membrane can be altered to differing extents. Aging studies of Nafion® /SiO2 nanocomposites were performed under ambient air, applied heat, water, refluxing methanol, and heated H2 SO4 . These studies monitored the Q 2 , Q3 , and Q4 populations of the sol-gel-derived nanocomposites via 29 Si solid state NMR spectroscopy. The end samples all had higher Q4 populations than the initial samples, indicating that condensation reactions did continue throughout the aging study. Several of the Nafion® /ORMOSIL hybrids contained vinyl moieties. Preliminary work exploring the effects of free-radical post-reactions of vinyl acetate (VA), vinyltrimethylsilane (VTMS), and methyl methacrylate (MMA) within the membrane were conducted. DMA, fluorescence, and solvent swelling investigated the variations in the membrane due to the presence of free-radical polymers. Significant differences in DMA plots and solvent swelling indicate that the membrane has been modified. Organic-inorganic nanocomposite materials can be exciting materials, possessing the properties of the polymer with the mechanical and thermal enhancement of the inorganic phase, if a good interface exists between the materials. Three silsesquioxane materials were synthesized and structurally characterized using FTIR and 13 C NMR techniques. The focus of these materials was enhancing the interfacial interactions, yielding a material with better mechanical and thermal properties. (Abstract shortened by UMI.)