Date of Award
Doctor of Philosophy
Materials Science and Engineering
Mark, D, Dadmun
Claudia J. Rawn, Gila E. Stein, Katharine L. Page
The structure of several materials important in the development of sustainable energy have been determined using multiple neutron scattering methods. Elucidating the structure-property relationships of these conductive polymer blends, microemulsions, and deep eutectic solvents (DES) provides correlation of material assembly to electro-chemical performance.
Conductive films of poly(3,4‑ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are found to organize into smaller domains with the addition of dimethyl sulfoxide(DMSO) to a pre-deposition solution. Addition of DMSO disrupts the aggregates and large domains within PEDOT:PSS, enabling alignment of the PEDOT fibrils within the PSS domains, and occurs in both spin-coated and spray-coated depositions. The spin-coated films have consistently smaller domain sizes, indicating the disruption of aggregates occurs when DMSO is added and the smaller domains in spin-coated films are due to faster evaporation rates of the deposited solution.
Microemulsions formed by mixing water, toluene, and an emulsifier of Tween-20® and 1-butonal create lamellar-like layers at surfaces potentially impacting charge transfer to electrodes. Layered structures are monitored for increased surface amphiphilicity and decreased water content in the emulsion. Decreased water in the emulsion results in decreased layer thickness, while increased amphiphilicity creates lamellae-like layers of nearly pure water and oil/emulsifier. The formation of these lamellae increase the surface area of the boundary between the water and the oil, creating a potential to increase charge transfer pathways.
Addition of a hydrogen bond acceptor, choline chloride(ChCl), to a hydrogen bond donor, glycerol, develops interactions between the molecules, forming a DES at 33% ChCl. With increased ChCl to the mixture, the glycerol interacts primarily with the chloride anion while the choline primarily interacts with other choline molecules. This assembly of potential hydrogen bond networks is crucial to the formation of the DES glyceline, where the dominant choline-choline interactions free the chloride ion to interact with the glycerol molecules.
Additionally, monitoring and controlling atomic vibrations in crystals integral to the execution of ultra-small-angle neutron scattering experiments offers insight to increase the signal-to-noise in USANS instruments. The combination of these investigations demonstrate the utility and promise of multiple neutron scattering techniques to advance several important classes of materials in soft matter energy research.
Heroux, Luke A., "Structure Analysis of Soft Energy Materials using Neutron Scattering. " PhD diss., University of Tennessee, 2021.