Programming the Dynamics of Active Colloids via Shape
Open Access
- Author:
- Brooks, Allan
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 12, 2019
- Committee Members:
- Ayusman Sen, Dissertation Advisor/Co-Advisor
Ayusman Sen, Committee Chair/Co-Chair
Ali Borhan, Committee Member
Thomas E Mallouk, Outside Member
Darrell Velegol, Committee Chair/Co-Chair
Darrell Velegol, Dissertation Advisor/Co-Advisor
Phillip E Savage, Program Head/Chair - Keywords:
- micromotors
active matter
colloids - Abstract:
- The objective of this dissertation is to use particle shape as a method to program the dynamical behaviors of active colloids. Microparticles driven out of equilibrium have been the subject of much research for the development of functional nanomachines. These "micromotors" can be driven by a number of forces --- chemical reactions, ultrasound, electric fields, and more. To move from bench-top demonstrations to functional applications, better programming techniques are needed to control micromotor behavior. Ideally, active colloids could be programmed at the individual particle level, enabling the encoding of different ``agents" operating with unique behaviors in the same environment. While some relatively simple tasks have been programmed into micromotors, precise control over a broad range of behaviors has yet to be achieved. To this end, tuning particle shape is a particularly attractive method to encode dynamic behaviors in active colloids. Nanofabrication techniques allow for the precise control of structure and can enable the rapid fabrication of many microparticles. Because particle shape is a continuous variable, particle geometry lends itself to being optimized for motor performance. This dissertation investigates the role of particle shape in two broad systems: micromotors powered by external electric fields and micromotors powered by chemical reactions. Both mechanisms are first explored with motors whose symmetry is only broken by particle geometry; their surface chemistry is homogeneous. These investigations provide intuition on the shape-directed design of active colloids and illustrate the power of such a programming strategy. Further, they build understanding of the propulsion mechanisms themselves; included in this dissertation are projects that developed from this gained understanding. These follow-up projects apply new mechanistic insights to explain the experimental results of others. Finally, particle shape is used to control the collective behaviors of assemblies of reaction-driven micromotors. The insights and approaches to shape-directed programming contained within this dissertation can be applied to a wide range of active colloidal systems. Geometric control of micromotors promises to be a powerful tool in the creation of functional colloidal machines.