Rheological and Colloidal Approaches to Characterizing and Producing Dispersions for Advanced Manufacturing 5120 views

Products made from particles and polymers are found everywhere in modern life. Seventy percent of all polymers contain particles whose dispersion optimizes desirable properties. Colloidal and interfacial phenomena drive important processes in industries from food processing to pharmaceuticals to petrochemicals. Novel multifunctional fluids and composites can be developed from new colloid systems. In this dissertation, I use rheological techniques and colloid theory to investigate novel manufacturing processes. The first task was to study the use of ultraviolet (UV)-curable polymeric coatings for electroplating processes. UV-curable polymers provide many potential benefits as coatings for the manufacturing of metallic parts, especially through the reduced time and labor costs of applying them in comparison to other material systems. Automated application of UV-curable coatings would enable significant further cost and time savings. Automation requires a more detailed understanding of the mechanical and interfacial properties of the maskants before and after curing. The shorter-chained burn-off materials showed greater adhesion and resistance to plating species than their peel-off counterparts. The focus on macro scale parts and the maskant mechanical properties represent a novel contribution to the UV-curable coating literature. The second process studied was the liquid-phase exfoliation of graphite into the two-dimensional nanomaterial graphene. There has been an explosion of interest in two-dimensional nanomaterials generally because of their many outstanding properties. A major limit in the practical use of graphene is the synthesis of large amounts with the desired properties, such as electronic conductivity or flake size. Liquid-phase exfoliation by shear is especially attractive because it is scalable and produces significantly fewer defects than older methods based on ultrasonication. I have evaluated liquid viscosity and dielectric constant as previously unstudied parameters relevant to the production of few-layer graphene by liquid-phase shear exfoliation and which could explain observations that the surface tension framework fails to describe. Through a rheological study, I demonstrated that a higher viscosity liquid, propylene glycol (PG), can produce more few-layer graphene by shear exfoliation than a lower viscosity liquid, the standard graphene solvent N-methyl-2-pyrrolidone (NMP), under identical conditions. This was followed up by a larger-scale study in an industrial impeller mixer, where PG produced equivalent quality material compared to that exfoliated in NMP, and at higher concentrations at all exfoliation times. Additionally, graphene dispersions in PG showed similar dispersion stability to those in NMP over the course of 160 hours and a greater predicted stability based on the second virial coefficient of the dispersions. This work on few-layer graphene produced by exfoliation should be generalizable to other two-dimensional nanomaterials. The fuller understanding of exfoliation and dispersion stability provided will enhance solvent selection and design for exfoliation of specific materials with characteristics tailored to specific applications. Additionally, these dispersions may be useful multifunctional high-performance fluids for applications like heat transfer or lubrication or as “inks” for manufacturing. They can also be a platform for further chemical modification of graphene and other 2D nanomaterials.

PHD (Doctor of Philosophy)

graphene; colloids; rheology

English

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2019-10-29