Paper Number
CS5                         My Program 

Session
Colloidal Suspensions and Granular Materials

Title
Flow irreversibility for translational and rotational motion in dense colloidal suspensions

Presentation Date and Time
October 20, 2025 (Monday) 11:10

Track / Room
Track 1 / Sweeney Ballroom A

Authors (Click on name to view author profile)

  1. Walker, Austin H. (Georgetown University, Physics)
  2. Del Gado, Emanuela (Georgetown University, Department of Physics)
  3. Urbach, Jeffrey (Georgetown University, Physics)
  4. Blair, Daniel L. (Georgetown University, Department of Physics)

Author and Affiliation Lines (in printed abstract book)
Austin H. Walker, Emanuela Del Gado, Jeffrey Urbach and Daniel L. Blair
Physics, Georgetown University, Washington, DC 20057

Speaker / Presenter 
Walker, Austin H.

Keywords
experimental methods; colloids; microscopy; non-Newtonian fluids; suspensions

Text of Abstract
We study the flow reversibility of dense colloidal suspensions to link micro-structure to bulk material properties and elucidate the connections between fundamental ideas in statistical physics: chaos, reversibility, and predictability. The translational displacements of particles within granular and colloidal systems have been extensively studied under externally applied oscillatory shear [1,2,3]. Using confocal-rheology, we image particles once per cycle under oscillatory shear to experimentally verify the irreversibility threshold for translational motion and measure the corresponding threshold for rotational motion. Our in-house synthesized colloidal OCULI particles [4] have an offset core-shell construction, providing a real-space quantification of the rotational dynamics of each individual particle. This novel construction allows us to independently measure the critical strain amplitude for irreversible translational and rotational motion. Furthermore, we will demonstrate how concentration and OCULI surface roughness shift the threshold of flow irreversibility. This work is supported by NSF DMR 2226485 [1] Hexner, D.; Levine, D. Hyperuniformity of Critical Absorbing States. Phys. Rev. Lett. 2015, 114 (11), 110602. https://doi.org/10.1103/PhysRevLett.114.110602. [2] J.R. Royer, P.M. Chaikin. Precisely cyclic sand: Self-organization of periodically sheared frictional grains, Proc. Natl. Acad. Sci. U.S.A. 112 (1) 49-53, https://doi.org/10.1073/pnas.1413468112 (2015). [3] Pine, D. J.; Gollub, J. P.; Brady, J. F.; Leshansky, A. M. Chaos and Threshold for Irreversibility in Sheared Suspensions. Nature 2005, 438 (7070), 997–1000. https://doi.org/10.1038/nature04380. [4] Yanagishima, T.; Liu, Y.; Tanaka, H.; Dullens, R. P. A. Particle-Level Visualization of Hydrodynamic and Frictional Couplings in Dense Suspensions of Spherical Colloids. Phys. Rev. X 2021, 11 (2), 021056. https://doi.org/10.1103/PhysRevX.11.021056.