Settling of Exopolymer-Secreting Particle

Recent experiments have shown a comet-tail-shaped halo of mucus or exopolymers surrounding sedimenting marine snow [R. Chajwa et al. Science 386, eadl5767 (2024)] and have a dramatic impact on carbon storage and sequestration in the Ocean. These biologically secreted exopolymers alters the viscosity of the surrounding fluid and exhibit non-Newtonian rheological properties that are functions of the native ecology in the ocean. In this study, we employ numerical simulations to investigate how the viscoelastic properties of the secreted mucus influence its dispersion around a settling particle, where we allow for shape anisotropy. Our simulations employ a finite difference method in prolate spheroidal coordinates to model the flow of complex fluids around spheroidal particles. The elasticity of the mucus, combined with its variable viscosity, impacts the settling behavior of these mucus-releasing particles. Specifically, the viscoelasticity and changing fluid viscosity generated by the mucus not only affect the settling speed and the length of the comet tail formed around spherical particles but also alter the sedimentation direction of anisotropic particles. Through our analysis of the exopolymer field in the simulations, we reveal the physical mechanisms driving these changes in particle behavior.