Date of Graduation
5-2018
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Engineering (PhD)
Degree Level
Graduate
Department
Mechanical Engineering
Advisor/Mentor
Millett, Paul C.
Committee Member
Zou, Min
Second Committee Member
Wejinya, Uche C.
Third Committee Member
Servoss, Shannon L.
Fourth Committee Member
Nair, Arun K.
Keywords
Bijel; Cahn-Hilliard; Electric Fields; Nanoparticles; Phase-field; Thin-film
Abstract
Bijels are a relatively new class of soft materials that have many potential applications in the technology areas of energy, medicine, and environmental sustainability. They are formed by the arrest of binary liquid spinodal decomposition by a dispersion of solid colloidal nanoparticles. This dissertation presents an in-depth simulation study of Bijels constrained to thin-film geometries and in the presence of electric fields. We validate the computational model by comparing simulation results with previous computational modeling and experimental research. In the absence of suspended particles, we demonstrate that the model accurately captures the rich kinetics associated with diffusion-based surface-directed spinodal decomposition. When chemically-neutral particles are included in the films, the simulations capture surface-modified Bijel formation, with stabilized domain structures comparable with the experimental observations of Composto and coworkers. Next, the Bijel morphology space is explored. Key parameters varied are the Bijel liquid phase composition and the Bijel film thickness. Simulations reveal a broad spectrum of structurally unique morphologies that have yet to be observed in experiments and which could have interesting applications in membrane science and other domains. Lastly, the tunability of thin-film Bijels using applied external electric fields is explored. To accomplish this the coupled Cahn-Hilliard Particle Dynamics computational model is modified to include the effects of liquid domain alignment and particle dipole-dipole interactions in the presence of an electric field. Dielectric contrast between liquid domains governs liquid domain alignment and dielectric contrast between colloidal particles and liquid matrix governs particle polarizability. Both were varied in simulations and the study reveals unique internal morphologies including those with through-thickness liquid channels. Results include identification of electric field effects on phase evolution and final morphology as well as relevant mechanisms. It was also found that particle chains act as nucleation sites for phase separation. Electric field effects and mechanisms on morphology are identified and compared with other morphology-tuning parameters such as particle loading and liquid-liquid composition. For the simulations in this dissertation, extensive analyses of surface-to-volume ratios, interfacial particle attachment statistics, and topological interfacial curvatures within the Bijels are presented for a complete characterization of their morphological structure.
Citation
Carmack, J. M. (2018). Mesoscale Computational Studies of Thin-film Bijels. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/2742
Simulations Animations
Included in
Engineering Physics Commons, Nanoscience and Nanotechnology Commons, Polymer and Organic Materials Commons
