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Forced microrheology of active colloids

Peng, Zhiwei and Brady, John F. (2022) Forced microrheology of active colloids. . (Unpublished)

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Particle-tracking microrheology of dilute active (self-propelled) colloidal suspensions is studied by considering the external force required to maintain the steady motion of an immersed constant-velocity colloidal probe. If the probe speed is zero, the suspension microstructure is isotropic but exhibits a boundary accumulation of active bath particles at contact due to their self-propulsion. As the probe moves through the suspension, the microstructure is distorted from the non-equilibrium isotropic state, which allows us to define a microviscosity for the suspension using the Stokes drag law. For a slow probe, we show that active suspensions exhibit a swim-thinning behavior in which their microviscosity is gradually lowered from that of passive suspensions as the swim speed increases. When the probe speed is fast, the suspension activity is obscured by the rapid advection of the probe and the measured microviscosity is indistinguishable from that of passive suspensions. Generally for finite activity, the suspension exhibits a velocity-thinning behavior -- though with a zero-velocity plateau lower than passive suspensions -- as a function of the probe speed. These behaviors originate from the interplay between the suspension activity and the hard-sphere excluded volume interaction between the probe and a bath particle.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper ItemJournal article
Peng, Zhiwei0000-0002-9486-2837
Brady, John F.0000-0001-5817-9128
Additional Information:Attribution 4.0 International (CC BY 4.0) We thank Hyeongjoo Row for useful discussions. This work is supported by the National Science Foundation under Grant No. CBET 1803662. The authors have no conflicts to disclose.
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Record Number:CaltechAUTHORS:20220707-204057698
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115400
Deposited By: George Porter
Deposited On:08 Jul 2022 21:52
Last Modified:31 Aug 2022 23:53

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