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Gong, Jiahao

University of British Columbia

Microorganisms often swim in complex and inhomogeneous fluids, with various shapes of microswimmers exhibiting distinct swimming behaviors in such environments. Understanding the coupling effect between the shape of these swimmers and the mechanical properties of the fluids can provide insights into different swimming strategies of real swimmers in nature. This understanding may also lead to more effective designs of synthetic microswimmers for medical, environmental, and computational applications. This thesis is devoted to a theoretical analysis of how various fluid environments affect the dynamics of particles with different shapes. Inspired by recent experimental research, we developed a simple analytical model to illustrate the reorienting and scattering phenomena of Chlamydomonas reinhardtii crossing sharp viscosity gradients. The governing equation of the reorientation process is analogous to the well-known Snell’s law of refraction. When we compared our theoretical results with experimental findings, we observed some quantitative discrepancies, probably due to the specific shape of the alga. To understand the effect of shape on viscotaxis, we extended the previous spherical squirmer model to a prolate spheroidal squirmer and investigated its swimming dynamics and energy expenditure in linear viscosity gradients. We found that spheroidal squirmers behave qualitatively similar to their spherical analogs. However, increased slenderness reduces the impact of viscosity gradients on their rotational dynamics, power dissipation, and swimming efficiency. These findings shed light on how swimming gait and shape drive the dynamics of active particles in inhomogeneous environments. Finally, we explored the effect of shape on particle dynamics in fluids governed by more complex constitutive laws, specifically viscoelastic fluids. We studied the propulsion dynamics for various asymmetrically shaped particles rotating in viscoelastic fluids and performed an optimization of propulsion speed under a fixed volume constraint. These results could be applied to develop new designs of active microrheometers.

Text

2024-10-21

Attribution-ShareAlike 4.0 International

http://hdl.handle.net/2429/89463

Mathematics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-sa/4.0/