Direct observation of colloidal aggregation by critical casimir forces

Daniel Bonn, Jakub Otwinowski, Stefano Sacanna, Hua Guo, Gerard Wegdam, Peter Schall

Research output: Contribution to journalArticlepeer-review


We present a refractive-index-matched colloidal system that allows direct observation of critical Casimir induced aggregation with a confocal microscope. We show that in this system, in which van der Waals forces are negligible, a simple competition between repulsive screened Coulomb and attractive critical Casimir forces can account quantitatively for the reversible aggregation. Above the temperature Ta, the critical Casimir force drives aggregation of the particles into fractal clusters, while below Ta, the electrostatic repulsion between the particles breaks up the clusters, and the particles resuspend by thermal diffusion. The aggregation is observed in a remarkably wide temperature range of as much as 15°. We derive a simple expression for the particle pair potential that accounts quantitatively for the temperature-dependent aggregation and aggregate breakup.

Original languageEnglish (US)
Article number156101
JournalPhysical Review Letters
Issue number15
StatePublished - Oct 8 2009

ASJC Scopus subject areas

  • General Physics and Astronomy


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