Graduation Semester and Year
Spring 2026
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry
Department
Chemistry and Biochemistry
First Advisor
Peter Kroll
Abstract
Porous materials have a wide range of applications. One of which is environmental remediation as a sorbent. Synthetic materials are beneficial as they have more selectivity compared to natural sorbents however, they are more costly. Recently, a publication produced an ambiently dried gel using a copolymer of polymethylhydrosiloxane (PMHS) and polydimethylsiloxane (PDMS) after modification with vinylmethyldimethoxysilane (VMDMS). PMHS is a byproduct of the silicone industry which makes the synthesis cheaper and more environmentally friendly. The precursor ratio must be tailored to account for the change in polymer used. In this study, various ratios of PMHS and VMDMS as well as different solvents in order to prepare a highly porous, flexible, superhydrophobic material for oil-water separations. Physical and chemical properties were studied using Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA). The water contact angle and oil sorption capacity of each gel was also determined. Some ratios and solvents were not compatible and resulted in significant pore collapse. Ultimately, an intact, flexible, superhydrophobic and oleophilic gel was made using PMHS instead of a copolymer with promising results for use in oil spill remediation.
Thermogravimetric analysis of the material described above yielded an interesting result which was investigated further. Despite using ultra-pure Ar, N2, and He, a substantial apparent mass gain was observed of 4 percentage points when pyrolyzed to temperatures above 700 °C and below 900 °C. After FT-IR and chemical analysis, the mass gain was attributed to oxidation. Additional testing pinpointed the source of oxidation as the “inert” gas used during TG analysis. The porous SiCO material becomes hypersensitive upon heating and may be used as a probe to test the level of oxidative impurities in thermal experiments.
Further analysis of this material shows the development of transient porosity between 600 and 700 °C which is subsequently lost at higher temperatures. Isotherms collected at each temperature between 600 and 1000 °C (increments of 100 °C) displays H3 hysteresis which is indicative of a considerable amount of meso- and macropores. This hierarchical porosity may play a role in the unusual oxidative behavior observed. Raman spectroscopy was used to study the evolution of free carbon. Samples heated to 800 °C with a 4 hour hold at 800 °C, 900 °C, and 1000 °C produce characteristic D and G bands. The ratio of these bands can be used to understand the structure and estimate a size of the free carbon generated.
Using different heating rates during thermogravimetric analysis allows one to employ various kinetic analysis methods to determine the activation energy of the different processes and define the reaction model. Here the Flynn-Wall-Ozawa method and Friedman analysis method were used. When the Friedman analysis was conducted, significant differences were observed for low heating rates compared to higher heating rates. Simulated data was generated and fit using a Frazer-Suzuki function to determine the reaction model. Fitting showed two distinct processes: the first corresponding to a diffusion-based process and the second resembling first order kinetics.
Keywords
Polymer, Polymer-Derived Ceramics, Porous Materials, Thermal Analysis
Disciplines
Materials Chemistry | Physical Chemistry
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Hayes, Hannah M., "Synthesis and Characterization of Polymethylhydrosiloxane-Based Materials: Environmental Remediation, Unusual Oxidative Behavior, and Kinetic Analysis" (2026). Chemistry & Biochemistry Dissertations. 2.
https://mavmatrix.uta.edu/chemistry_dissertations2/2