Photochemical Sciences Ph.D. Dissertations

Title

Investigation of Structured Fluids Properties at the Molecular Level: Insight from Electron Paramagnetic Resonance (EPR) Spin Prober

Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Malcolm D.E. Forbes (Advisor)

Second Advisor

Pavel Anzenbacher (Committee Member)

Third Advisor

Joseph Furgal (Committee Member)

Fourth Advisor

Nermis Mieses (Other)

Abstract

This dissertation describes the study of the dynamics of structured fluids (Non-Newtonian Fluids) at molecular level, using Electron Paramagnetic Resonance in both Steady–State (SSEPR) and Time–Resolved (TREPR) modes. Nuclear Magnetic Resonance (NMR) was also used to gain information with different nuclear spin probes. Changes in the microstructure of these unusual liquids due to interparticle interactions at the molecular level play a vital role in understanding their dynamics. The table free radicals TEMPO, TEMPONE, and galvinoxyl were utilized as spin probes to study the interparticle interactions in nano silica-based Aerosil and Xanthan Gum structured fluids with organic solvents. Different solvent polarities, different loadings of Aerosil R972, Aerosil R711, and Aerosil 200, temperature, and strain force were all investigated. EasySpin software was used to provide simulations with the "garlic" to find the rotational correlation time of spin probes. In TREPR experiments, TEMPO and TEMPONE were used as spin probes, while benzophenone in benzene and benzil in toluene were utilized as photosensitizers to study the Radical Triplet Pair Mechanism (RTPM). Spin probe effects on RTPM are demonstrated by emissive spin polarized TREPR spectra. In addition to using proton NMR, 4–methylanisole was used asa nuclear spin probe to examine the dynamic motion of the Aerosils, and also study different solvent polarities, loading effects, and temperature dependence. These results clearly illustrate that the physical properties of structured fluids are sometimes strongly affected by these various parameters. Changes in spectral linewidth were attributed to differences in the correlation time τ (100 ps to 100 ns) which provides quantitive information regarding the microviscosity. The TREPR spectra linewidth change demonstrated the structured fluids provide a medium for the strong spin interaction between excited triple states and stable free radicals; this is a new way to study the dynamics of these substances at the molecular level. This research used a unique way to demonstrate the intramolecular interaction of Nano-silicon in different surroundings. In the future this research method could also be used to analyze the properties of rubber, cosmetics, construction material, and foods directly to optimize energy use in their production and application.

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