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arXiv · 2605.16723

Hydrodynamic cascade drives tumbling in sheared colloidal rod suspensions

Lucas H. P. Cunha·Paul F. Salipante·Peter D. Olmsted·Steven D. Hudson
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Abstract

Modeling the dynamics of colloidal rods remains a central challenge in soft-matter physics due to the anisotropic and long-ranged nature of their interactions. Hydrodynamic interactions in rods suspensions are often assumed to be screened or too week to play any role in semi-dilute regimes, yet we find here these assumptions to break down at shear rates and concentrations that are often attained in experiments. Using particle-based simulations and scaling analysis, we uncover a cascade of tumbling events driven by hydrodynamic coupling among neighboring rods. This collective dynamics disrupts flow alignment and leads to a pronounced increase in viscosity and normal stress differences, in qualitative agreement with recent experiments. The discovery of this hydrodynamically-promoted cascade effect calls for a revision of existing constitutive models for colloidal rods and highlights hydrodynamic coupling as a key mechanism governing collective dynamics in highly anisotropic suspensions.

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Lucas H. P. Cunha, Paul F. Salipante, Peter D. Olmsted, Steven D. Hudson. 2026-05-16. Hydrodynamic cascade drives tumbling in sheared colloidal rod suspensions. https://arxiv.org/abs/2605.16723

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