(28e) Using Janus Particles to Control Mixing/Segregating of Adhesive Granular Materials in Rotating Tumblers

Processing of fine powders is a relevant operation in many industries, from pharmaceuticals to material synthesis. As the size of the particles decreases, adhesive forces due to van der Waals interactions become important and can have a non-trivial, but difficult to predict impact on the mixing/segregation tendency of the material. The aim of this work is to control the final asymptotic state of van der Waals adhesive systems through the addition of "helper" particles that can promote mixing or segregation. These amphiphilic "helper" particles --also called Janus Particles-- act as a bridges between particles, alternatively promoting mixing in a system that would otherwise segregate (surfactant particles) or separating a specific kind of particle from a mixture (extractant particles). Phase space diagrams of the expected behavior are analytically identified by comparing the interaction forces in the system: the strengths of those that promote mixing are compared with the ones that enhance segregation (including those interactions bridged by Janus particles), and the final state of the system is determined by the interactions that predominate. The predictions are then tested against results obtained by DEM simulations of the system including Janus Particles, which are further compared to both the binary adhesive system and the freeflow case.