Towards controlling active matter : from light control to topological traps
Abstract/Contents
- Abstract
- Activity can organize matter in unique configurations inaccessible to equilibrium systems. The potential to harness principles of self-organization by studying active matter has immense implications in engineering and design. In the first part of this dissertation, I propose a self-driven microfluidic device propelled by a suspension of active, light-controllable molecular motors. Surface-driven flows are ubiquitous in nature, from subcellular cytoplasmic streaming to organ-scale ciliary arrays. We model how confined geometries can be used to engineer complex hydrodynamic patterns driven by activity prescribed solely on the boundary. Specifically, we simulate light-controlled surface-driven flows, probing the emergent properties of a suspension of active colloids that can bind and unbind from surfaces of a closed microchamber, together creating an active carpet. The attached colloids generate large scale flows that in turn can advect detached particles towards the walls. Switching the particle velocities with light, we program the active suspension and demonstrate a rich design space of flow patterns characterised by topological defects. We derive the possible mode structures and use this theory to optimize different microfluidic functions including hydrodynamic compartmentalisation and chaotic mixing. Our results pave the way towards designing and controlling surface-driven active fluids. In the second part of this disseration, I shift gears and discuss a structure formed by the collective motion of a species of gliding, filamentous cyanobacteria we term the "active spiral". How persistent yet dynamic patterns can form in motile active systems remains an open question. We leverage the ability to segment and track each filament individually to gain insight into this question, giving us single-particle resolution into the spiral dynamics. Due to the reversible gliding motility of individual filaments in the spiral, the filaments shear past each other with no coherent system-level vorticity, forming highly dynamic structures exhibiting radial material flux. These rearrangements are primarily driven by rules of interaction between motile tips. We enumerate these rules of interaction on a polar coordinate lattice, and show we can predict material flux within the system as a result. We also present the discovery of a new topological trap in active spirals, which creates un-crossable boundaries in an otherwise dynamic structure capable of material movement. Interestingly, these topological traps arise purely from the geometry of long filaments with winding number greater than zero. Understanding the dynamics of an active system with single filament resolution enables the detailed understanding of particle interactions, a necessary step toward controlling active matter.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2022; ©2022 |
| Publication date | 2022; 2022 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Gong, Xingting |
|---|---|
| Degree supervisor | Bryant, Zev David |
| Degree supervisor | Prakash, Manu |
| Degree supervisor | Spakowitz, Andrew James |
| Thesis advisor | Bryant, Zev David |
| Thesis advisor | Prakash, Manu |
| Thesis advisor | Spakowitz, Andrew James |
| Thesis advisor | Greenleaf, William James |
| Degree committee member | Greenleaf, William James |
| Associated with | Stanford University, Department of Applied Physics |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Xingting Gong. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis Ph.D. Stanford University 2022. |
| Location | https://purl.stanford.edu/df641yb1380 |
Access conditions
- Copyright
- © 2022 by Xingting Gong
- License
- This work is licensed under a Creative Commons Attribution 3.0 Unported license (CC BY).
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