Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Frederick MacDonnell

Abstract

Research to design, synthesize, and characterize porous materials is a rapidly growing field due to porous materials’ potential use in a wide range of applications. For any application, insights into the structure formation parameters and properties relating to those parameters are highly desired. This thesis deals with the combination of two classes of materials, aerogels and polymer-derived ceramics. Polymer Derived Ceramics (PDCs) are processed using liquid-based, hydrocarbon polymeric precursors at lower temperature, followed by heat treatments at higher temperature. Silicon oxycarbide (SiCO) is one type of PDC. Various types and ranges of porosity can be introduced into SiCO when using sol-gel methods of synthesis. These adaptations can be exploited for different applications such as gas separation membranes, environmental remediation, or lithium-ion storage. Such porous SiCO aerogels are the focus of this study. The choice of precursors. synthesis conditions, and post-synthesis processing influence unique physical and chemical properties of the final SiCO ceramics by introducing specific microstructure, porosity, content of free carbon, and specific surface are. This report of the research consists of three sections: effect of synthesis conditions on porosity, the interdependence of the assessment of microstructure and the techniques utilized for evaluating it, and the role of precursor role on the composition of SiCO and the resulting microstructure. In the first section we investigate the effect of the synthesis solvent, as one of the important synthesis conditions, and its systematic correlation with Hansen Solubility Parameters (HSP) with the resulting SiCO microstructure. In the second section, we apply different methods for characterizing porosity, highlighting a recently developed technique known as Differential Hysteresis Scanning (DHS) to quantify hierarchical connectivity in two SiCO aerogels. This technique contrasts strikingly the structures obtained from two different solvents used in the synthesis, and characterizes their respective changes on pyrolysis to 1000 °C. Finally, we study a novel crosslinking agent as a substitute for DVB to explore the possibility of new microstructures, functionalities, and different chemical compositions of the SiCO ceramics before and following calcination.

Keywords

Porosity, Silicon oxycarbide, Aerogels

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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