Paper Number
CS32                         My Program 

Session
Colloidal Suspensions and Granular Materials

Title
Flow-induced lamellar ordering in attractive suspensions

Presentation Date and Time
October 21, 2025 (Tuesday) 5:05

Track / Room
Track 1 / Sweeney Ballroom A

Authors (Click on name to view author profile)

1. Moghimi, Esmaeel (Department of Physics, Georgetown College, Georgetown Univer)
2. Vinutha, H A (Department of Physics, Georgetown College, Georgetown Univer)
3. Walker, Austin H. (Georgetown University, Physics)
4. Del Gado, Emanuela (Georgetown University, Department of Physics)
5. Blair, Daniel L. (Georgetown University, Department of Physics)
6. Urbach, Jeffrey (Georgetown University, Physics)

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

Speaker / Presenter 
Moghimi, Esmaeel

Keywords
colloids; flow-induced instabilities; microscopy; non-Newtonian fluids; selft-assemblies; suspensions

Text of Abstract
We investigate microstructural changes that occur during oscillatory shear flow in an intermediate-volume-fraction colloidal gel, using rheo-confocal experiments and simulations. The system consists of a model depletion colloid–polymer mixture, composed of hard-sphere colloidal particles and non-adsorbing linear polymer chains. Our results reveal three distinct structural regimes depending on the strain amplitude and frequency of the applied oscillatory shear. At large strain amplitudes, the structure is fully broken, resulting in a more homogeneous dispersion. At low strain amplitudes, the system forms heterogeneous, amorphous structures. Remarkably, at intermediate strain amplitudes and very high frequencies, we observe the formation of a novel lamellar structure: particles organize into layers aligned with the flow direction, separated by solvent-rich regions. Rheo-confocal imaging shows that particles initially form monolayer sheets, which grow in thickness with continued shearing. These lamellar structures exhibit high stability even after flow cessation. Complementary simulations indicate that particle–particle friction is a key factor driving and stabilizing this layered organization. This discovery of flow-induced lamellar ordering in attractive suspensions reveals a new class of shear-induced structures with potential implications for processing and material design in soft matter systems.