title: Sheared active fluids: thickening, thinning, and vanishing viscosity.
abstract: We analyze the behavior of a suspension of active polar particles under shear. In the absence of external forces, orientationally ordered active particles are known to exhibit a transition to a state of nonuniform polarization and spontaneous flow. Such a transition results from the interplay between elastic stresses, due to the liquid crystallinity of the suspension, and internal active stresses. In the presence of an external shear, we find an extremely rich variety of phenomena, including an effective reduction (increase) in the apparent viscosity depending on the nature of the active stresses and the flow-alignment property of the particles, as well as more exotic behaviors such as a nonmonotonic stress-strain-rate relation and yield stress for large activities.
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Giomi
authors.forename: Tanniemola B
authors.initials: TB
authors.lastname: Liverpool
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Marchetti
mesh_terms: D016880:Anisotropy; D001412:Bacillus subtilis / Q000378:metabolism; D018407:Bacterial Physiological Phenomena; D001703:Biophysics / Q000379:methods*; D003599:Cytoskeleton / Q000378:metabolism; D050866:Liquid Crystals; D008954:Models, Biological; D009068:Movement; D012212:Rheology; D033081:Shear Strength; D013314:Stress, Mechanical; D014783:Viscosity