title: Order-to-disorder transition in ring-shaped colloidal stains.
abstract: A colloidal dispersion droplet evaporating from a surface, such as a drying coffee drop, leaves a distinct ring-shaped stain. Although this mechanism is frequently used for particle self-assembly, the conditions for crystallization have remained unclear. Our experiments with monodisperse colloidal particles reveal a structural transition in the stain, from ordered crystals to disordered packings. We show that this sharp transition originates from a temporal singularity of the flow velocity inside the evaporating droplet at the end of its life. When the deposition speed is low, particles have time to arrange by Brownian motion, while at the end, high-speed particles are jammed into a disordered phase.
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology Mesa+ Institute, University of Twente, 7500AE Enschede, The Netherlands. a.g.marin@utwente.nl
authors.forename: Álvaro G
authors.initials: ÁG
authors.lastname: Marín
authors.forename: Hanneke
authors.initials: H
authors.lastname: Gelderblom
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Jacco H
authors.initials: JH
authors.lastname: Snoeijer
mesh_terms: D055598:Chemical Phenomena; D003069:Coffee / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D003460:Crystallization; D014835:Volatilization
chemical_list: D003069:Coffee; D003102:Colloids