title: Influence of humidity on tribo-electric charging and segregation in shaken granular media.
abstract: We study the effect of humidity on the charge accumulation of polymer granulates shaken vertically in a stainless steel container. This setup allows us to control the humidity level from 5% to 100%RH while performing automated charge measurements in a Faraday cup directly connected to the shaking container. We find that samples of approximately 2000 polymer spheres become highly charged at low humidity levels (<30%RH), but acquire almost no charge for humidity levels above 80%RH. The transition between these two regimes does depend on the material, as does the sign of the charge. For the latter we find a correlation with the contact angle of the polymer with only very hydrophilic particles attaining positive charges. We show that this humidity dependence of tribo-charging can be used to control segregation in shaken binary mixtures.
authors.affiliation: MPI Dynamics and Self-Organization, Am Fassberg 17, 37077 Göttingen, Germany. andre.schella@ds.mpg.de.
authors.forename: André
authors.initials: A
authors.lastname: Schella
authors.affiliation: MPI Dynamics and Self-Organization, Am Fassberg 17, 37077 Göttingen, Germany. andre.schella@ds.mpg.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Herminghaus
authors.affiliation: MPI Dynamics and Self-Organization, Am Fassberg 17, 37077 Göttingen, Germany. andre.schella@ds.mpg.de and Institute for Multiscale Simulation, Nägelsbachstrasse 49b, 91052 Erlangen, Germany. matthias.schroeter@fau.de.
authors.forename: Matthias
authors.identifier: http://orcid.org/0000-0002-8332-5585
authors.initials: M
authors.lastname: Schröter