title: Critical onset of layering in sedimenting suspensions of nanoparticles.
abstract: We quantitatively study the critical onset of layering in suspensions of nanoparticles in a solvent, where an initially homogeneous suspension, subject to an effective gravity a in a centrifuge, spontaneously forms well-defined layers of constant particle density, so that the density changes in a staircaselike manner along the axis of gravity. This phenomenon is well known; yet, it has never been quantitatively studied under reproducible conditions: therefore, its physical mechanism remained controversial and the role of thermal diffusion in this phenomenon was never explored. We demonstrate that the number of layers forming in the sample exhibits a critical scaling as a function of a; a critical dependence on sample height and transverse temperature gradient is established as well. We reproduce our experiments by theoretical calculations, which attribute the layering to a diffusion-limited convective instability, fully elucidating the physical mechanism of layering.
authors.affiliation: Physics Department and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: A V
authors.initials: AV
authors.lastname: Butenko
authors.affiliation: Chemistry Department and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: P M
authors.initials: PM
authors.lastname: Nanikashvili
authors.affiliation: Chemistry Department and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Zitoun
authors.affiliation: Physics Department and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: E
authors.initials: E
authors.lastname: Sloutskin
mesh_terms: D004058:Diffusion; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013535:Suspensions / Q000737:chemistry
chemical_list: D012997:Solvents; D013535:Suspensions