Date of Award
2022
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry
Specialization
Materials Science
Department
Chemistry
First Advisor
William B. Euler
Abstract
Poly(vinylidene fluoride) (PVDF) is a common semi-crystalline polymer with a wide range of industrial applications due to electro-activity. A higher fraction of the polar beta phase in PVDF is essential to achieve advanced properties. In this project, we use transition metal ions to achieve a higher beta fraction, and further analysis is carried out to identify structure-property relationships of the material and uncover possible applications.
We fabricate composite thin films mainly using dip coating and spin coating methods. In manuscript one, we thermally treat the fabricated metal nitrate hydrate doped thin films to synthesize metal oxides in PVDF, which is highly demanded as nano generators and efficient catalytic systems. In this thermal oxide synthesis process, we observe a catalytic activity of PVDF, which synthesizes 2+ charged metal oxides at a lower temperature than its pure salt state. This phenomenon is due to the internal electric field of PVDF, which is strong enough to orient reactant molecules and convert reactants into products even in a low-energy environment. Here we report the catalytic activity of PVDF on 2+ charged metal nitrate thermal decomposition reactions for the first time, and this catalytic activity is little to none when PVDF is doped with 3+ charged metal ions.
In manuscript two, the synthesized metal oxide-PVDF composite materials were thermally treated further to identify any effect of PVDF and transition metal oxides on each other. Analysis suggests no effect from metal oxide to thermal decomposition of PVDF that happens above 400 °C while PVDF changes the structure of metal oxides. Here, PVDF acts as a potent reducing agent at higher temperatures to reduce metal oxides into intermediate reduced oxides and convert them into metals. This reducing activity is due to the PVDF decomposition product carbon, which can reduce metal oxides while oxidizing themselves to CO2 and CO.
The third manuscript discusses any effect of metal ion-doped PVDF thin films on photophysical properties of common cationic xanthene dye Rh6G. When Rh6G is deposited on 2+ charged metal ion-PVDF thin films, there is a significant enhancement of both absorption and emission while minimizing aggregate formation is substantial. The analysis shows that these enhanced properties result from the coupling effect of the charge of metal ions and the polar beta phase of PVDF. Again, there is no significant absorption and emission enhancement when PVDF is doped with 3+ charged metal ions.
So far, the behavioral changes between 2+ and 3+ metal ions have remained unclear. The fourth manuscript is about an attempt to identify nuclear level insight into 3+ charged metal ions using Fe3+/PVDF material to achieve using Mossbauer spectroscopy. According to data, Fe3+ at room temperature thin films are in high spin electronic configuration with an asymmetric electric field environment due to non-polar alpha/amorphous and polar beta phases. When these samples are heated to higher temperatures, the Fe3+/PVDF composite acts as a NO2 decomposition system, making it possible to use as an environmentally friendly catalytic system. According to Mossbauer spectroscopic data, Fe2+ formation happens at higher temperatures, suggesting a reduction reaction occurs in the system. Here we propose an equilibrium catalytic cycle with a forward reaction that reduces Fe3+ into Fe2+ while decomposing NO2, and a backward reaction regenerates Fe3+.
Recommended Citation
Sumathirathne, Lasanthi, "A STUDY OF STRUCTURE-PROPERTY RELATIONSHIPS IN TRANSITION METAL ION-PVDF THIN FILMS/COMPOSITES AND APPLICATIONS" (2022). Open Access Dissertations. Paper 1380.
https://digitalcommons.uri.edu/oa_diss/1380
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