Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Xiang Cheng, Xinliang Xu, Stuart A. Rice, Aaron R. Dinner, Itai Cohen

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Colloidal suspensions self-assemble into equilibrium structures ranging from face- and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows.

Original languageEnglish (US)
Pages (from-to)63-67
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number1
StatePublished - Jan 3 2012


  • Colloids
  • Shear-induced structure


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