Date on Master's Thesis/Doctoral Dissertation

5-2021

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Degree Program

Chemical Engineering, MS

Committee Chair

Willing, Gerold

Committee Member

Williams, Stuart

Committee Member

Jaeger, Vance

Author's Keywords

image; analysis; python; colloidspy; bimodal; colloids

Abstract

Colloids are suspensions of two or more phases and have been topics of research for advanced, tunable materials for decades. Stabilization of colloids is typically attributed to thermodynamic mechanisms; however, recent studies have identified transport or entropic mechanisms that can potentially stabilize a thermodynamically unstable colloidal system. In this study, suspensions of silsesquioxane microparticles and zirconia nanoparticles were dispersed in a nitric acid solution and allowed to aggregate for 8-12 days in microgravity aboard the International Space Station. The suspensions were subsequently imaged periodically at 2.5x magnification. Due to the inadequacy of existing image analysis programs, the python package “Colloidspy” was developed to process these images and extract cluster boundaries. Trends of cluster area over time revealed two distinct behaviors. Some samples showed very low cluster growth rates and high cluster areas compared to microparticle size, while others showed an initial rapid growth phase, slowing to the low cluster growth rates of the other samples. The presence of this characteristic nonlinear phase coupled with the striking similarity in final growth rates of all samples suggests that the undocumented time between sample mixing and start of imaging may have been large enough that there was nonlinear growth in all samples, but only the final slow growth phase was captured in many of the samples. This type of behavior is not consistent with the linear agglomeration predictions of existing theory based on thermodynamic stabilization, but could be explained by the lack of buoyancy forces in microgravity allowing the space between clusters to increase as small clusters are incorporated into larger agglomerations. Further agglomeration could have been dominated by transport limitations even through the solution is still thermodynamically unstable. Further study into the role of transport mechanisms in dilute colloidal systems in microgravity should be conducted to shed further light on this unusual behavior.

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