Precipitation Dynamics at the Solution-Solution Interface in Confined Geometries, and the Effects of Organics on Precipitate Evolution

Precipitate produced by the interaction of aqueous reactant solutions in a microchannel is evaluated through instrumental analysis and numerical modeling. Instrumental analysis of analogs of iron sulfide, iron carbonate, and iron phosphate minerals and the effect of modeled ionic strength and mass transport mechanisms are presented. Implications on fluid dynamics due the production of colloids at a solution-solution interface is developed. A phenomenon of electroless reduction in this system transitioning to self-catalyzed electrodeposition is presented in light of the dynamics previously discussed and is used as an example of the convergent effects of coupled physiochemical systems on the microscale. All three of the above results (precipitate analysis, fluid and mass transport dynamics, and coupled physiochemical systems) are leveraged to present results of the interaction of organic species with precipitating iron sulfide material. It is found that the presence of organic species has a strong impact on the morphology of iron sulfide mineral analogs, and that morphology may be diagnostic for the presence of organics during formation even when Raman spectra show no signs of extant organic material. This has profound implications for the use of autonomous rovers in exploring the organic-mineral interactions of ancient aqueous systems such as Mars’s Jezero Crater.Ph.D

Characterization of Polyhydroxybutyrate-Based Composites Prepared by Injection Molding

The waste generated by single-use plastics is often non-recyclable and non-biodegradable, inevitably ending up in our landfills, ecosystems, and food chain. Through the introduction of biodegradable polymers as substitutes for common plastics, we can decrease our impact on the planet. In this study, we evaluate the changes in mechanical and thermal properties of polyhydroxybutyrate-based composites with various additives: Microspheres, carbon fibers or polyethylene glycol (2000, 10,000, and 20,000 MW). The mixtures were injection molded using an in-house mold attached to a commercial extruder. The resulting samples were characterized using microscopy and a series of spectroscopic, thermal, and mechanical techniques. We have shown that the addition of carbon fibers and microspheres had minimal impact on thermal stability, whereas polyethylene glycol showed slight improvements at higher molecular weights. All of the composite samples showed a decrease in hardness and compressibility. The findings described in this study will improve our understanding of polyhydroxybutyrate-based composites prepared by injection molding, enabling advancements in integrating biodegradable plastics into everyday products