arXiv subjects

Qingzhi Zou

Publications and source records attributed to Qingzhi Zou.

2 recordsLinked to original sources

arXiv2025

Is the active suspension in a complex viscoelastic fluid more chaotic or more ordered?

The habitat of microorganisms is typically complex and viscoelastic. A natural question arises: Do polymers in a suspension of active swimmers enhance chaotic motion or promote orientational order? We address this issue by performing lattice Boltzmann simulations of squirmer suspensions in polymer solutions. At intermediate swimmer volume fractions, comparing to the Newtonian counterpart, polymers enhance polarization by up to a factor of 26 for neutral squirmers and 5 for pullers, thereby notably increasing orientational order. This effect arises from hydrodynamic feedback mechanism: squirmers stretch and align polymers, which in turn reinforce swimmer orientation and enhance polarization via hydrodynamic and steric interactions. The mechanism is validated by a positive correlation between polarization and a defined polymer-swimmer alignment parameter. Our findings establish a framework for understanding collective motion in complex fluids and suggest strategies for controlling active systems via polymer-mediated interactions.

cond-mat.soft↗

arXiv2025

Protocol to evaluate the viscoelastic response of a polymer suspension to an active agent via oscillatory shear rheometry

Microorganisms inhabit viscoelastic environments, where their locomotion can deform polymers and trigger local complex viscoelastic responses. However, a systematic approach to quantify such responses remains lacking. Here, we propose a protocol that maps the shear effect induced by an active agent to oscillatory shear rheometry. The central idea is to establish a correspondence between the mean shear rate generated by swimming and that produced by an oscillating plate. In this mapping, the swimming velocity and active stress are translated into an effective oscillation frequency and strain amplitude. The resulting viscoelastic response can then be evaluated by standard oscillatory rheometry. The protocol is validated using lattice Boltzmann simulations of a squirmer embedded in polymer solutions. Our framework is generic and can be naturally extended to active microrheology, providing a pathway to quantify swimmer-induced viscoelasticity.

cond-mat.soft↗