Description
- Abstract:
- Active matter systems remain in a far-from-equilibrium state due to the motion generated at small scales by their self-driven constituents. These systems can exhibit complex behavior, such as collective motion and pattern formation, and understanding the governing principles of active matter systems is tremendously challenging. The active fluids studied here are artificial systems assembled from kinesin-driven bundled microtubule networks. We focus on characterizing the three-dimensional dynamical behavior and structure of the active fluids, subject to different confining geometries. The systems are measured using an epi-fluorescence microscope equipped with two-color fluorescent imaging and synchronized z-scanning. The fluorescently-labeled microtubules (red) and the dispersed passive fluorescent tracer particles (blue) are simultaneously observed at multiple z-positions. A three-dimensional tracking method, using the Airy disks of diffracted particles, extends the measurement to the entire observation volume. The active systems exhibit transitions between two dynamical states — a chaotic turbulent state and a coherent state — depending on the confining geometry. The turbulent flows have no net transport while, in contrast, the coherent flows exhibit long-term self-pumping motion. We find that the self-pumping motion correlates with a three-dimensional flow structure, which is affected by the dimension and the surface treatment of the confinement. Besides, the coherent flows can be scaled across different dimensions and surface conditions. The influence of boundaries is further studied in the chaotic turbulent state of bulk active systems. Far from confining boundaries, the active systems exhibit small-scale isotropy, however, we obtain evidence of large-scale collective motion that extends beyond the scale of our measurement. As the confinement increases, the active systems preserve the small-scale isotropy, but demonstrate increasing large-scale anisotropy, a decrease in the temporal correlation (flow "memory") and a reduction in the characteristic size of the structure. Lastly, our results show that the large-scale dynamics in the active systems, either in the turbulent state or in the coherent state, hardly affect the micrometer-scale interaction between an active microtubule bundle and the motion of its nearby passive tracer particles.
- Notes:
- Thesis (Ph. D.)--Brown University, 2018
Access Conditions
- Rights
- In Copyright
- Restrictions on Use
- Collection is open for research.
Citation
Fan, Yi,
"Three-dimensional measurements of dynamics and structure in kinesin-driven active fluids"
(2018).
Engineering Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/5seb-jb92
