Speaker
Description
The development of engineered active colloids that harness the chemical energy of the environment to move has enabled one to mimic and dissect mechanisms in biological systems while opening doors to multiple applications: bioremediation, micromixing, micromachinery, drug delivery, and more. However, the application of active colloids for biomedical applications must consider the complex nature of most biological fluids, which contain large macromolecules and display viscoelastic and non-Newtonian rheology.
Recent experiments showed that active colloids propelling through a polymer solution experience a drastically enhanced rotational diffusion and can rotate spontaneously due to an instability the origin of which is not understood. Earlier work suggests that the instability arises from the advection of polymers around the colloid and requires a fore-aft asymmetric interaction between the particle and the polymers.
Here, we go beyond the study of the instability and we employ a fluctuating hydrodynamics approach developed in our group to study the Brownian dynamics and the spontaneous rotation of a spherical Janus active particle moving through a polymer solution. We model the evolution of the polymer concentration using a stochastic advection-diffusion equation that includes the thermal fluctuations of the polymer concentration. The results show that driving a Janus particle out of equilibrium in a polymer solution has a profound impact on its Brownian dynamics. In agreement with the experiments, we find that the rotational diffusion coefficient is drastically enhanced before the onset of the spontaneous rotation. Our work demonstrates the importance of considering the colloidal nature of polymer solutions and highlights the challenges of controlling active matter in a complex fluidic environment.
