title: Granular labyrinth structures in confined geometries.
abstract: Pattern forming processes are abundant in nature. Here, we report on a particular pattern forming process. Upon withdrawal of fluid from a particle-fluid dispersion in a Hele-Shaw cell, the particles are shown to be left behind in intriguing mazelike patterns. The particles, initially being uniformly spread out in a disc, are slowly pulled inwards and together by capillary and pressure forces. Invading air forms branching fingers, whereas the particles are compiled into comparably narrow branches. These branches are connected in a treelike structure, taking the form of a maze. The characteristic length scale within the structure is found to decrease with the volume fraction of the particles and increase with the plate separation in the Hele-Shaw cell. We present a simulator designed to simulate this phenomenon, which reproduces qualitatively and quantitatively the experiments, as well as a theory that can predict the observed wavelengths.
authors: Department of Physics, University of Oslo, Oslo, Norway. hak@fys.uio.no
authors: Henning Arendt
authors: HA
authors: Knudsen
authors: Bjørnar
authors: B
authors: Sandnes
authors: Eirik Grude
authors: EG
authors: Flekkøy
authors: Knut Jørgen
authors: KJ
authors: Måløy