Simulation of the adhesion-moments caused by van der Waals-interactions between rough particles and smooth walls in gaseous environment

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Particle-particle and particle-wall contacts are crucial for the movement behaviour of particle-collectives. Particularly at non spherical objects with flattening or roughnesses there is insufficient information of scale (position) and broadness of the allocation (scattering) of the expected interactions concerning sliding, rotating and overturning of the contact-partners. For the first two years of work on this sub-project one tried to achieve the following two main goals: Development of models for sliding, rotating and overturning of the smooth sphere with flattening and the rough sphere with two point contact facing a smooth wall in gaseous environment. Creation of a simulation for the calculation of complete distribution functions of the adhesion moments of the contact-partners. Common ground of both goals is the description of resistance against external loads caused by shear, torsion and bending forces. In the last two years the particle-building-routine was improved to fit real conditions better. The dependency of the adhesion force built up by an atom and its wall distance has been examined. Further there have been implemented different atomic lattices and a material porosity into the simulation. The calculated data according to adhesion-force and -moment have been compared to the experimental results of other PiKo sub-projects. The anisotropic behaviour of the adhesion-moment for the rough particle was examined. In the next two years the surface of the simulated particle should be influenced further. A bigger number of roughnesses with different geometry should be placed on the surface and their influence on both the adhesion-force and the -moment should be investigated. The measurement of the adhesion-moment is not possible and by now not planned within the SPP PiKo. Therefore the existing ESEM (Environmental Scanning Electron Microscope) of the Department should be upgraded with a micromanipulator and a spring table. With this equipment it would be possible to measure the adhesion-moment and the sliding-resistance force of particles. The fundamental basis of the simulation is still the calculation of the discrete interactions between the involved atoms or molecules of the contact partners and the superpositioning of those to a total interaction.