Adhesion farces between rough silica particles under humid conditions
Abstract
Adhesion forces between granular particles delicately depend on the amount of adsorbed condensed water from ambient atmosphere. Liquid water forms bridges in the cavities separating the particles, giving rise to the so called capillary forces which, in most cases, dominate the van der Waals and long range electrostatic interactions. Capillary forces promote the undesirable agglomeration of particles to large clusters, thereby hindering the flowability of powders in process containers. In process engineering macroscopic theories based on the Laplace pressures are used to estimate the strength of the capillary forces. However, especially when ultrafine powders with d < 10μm are treated where either the particles themselves or the roughness on the particle surface are in the nano-scale, those theories can fail. Molecular dynamic simulations can help to give better insight into the water particle interface and to complement interaction forces in regions not accessible to AFM experiments. Small atomistically smooth silica nanoparticles have been treated in the first year of the project to validate the applied atomistic force field (ClayFF). Force versus distance curves as well as adhesion energies between wetted silica wafer and nano particles for different amounts of adsorbed liquid water are encouraging and show good agreement with AFM experiments. Thus, by introducing coarse graining methods in the next project period, we will proceed to larger particles exhibiting roughness in the nano-scale, thereby studying adhesion forces in dependence of varying relative humidity. Our investigations will be validated by AFM measurements performed within the SPP.
Silica particles adhesion forces water bridges molecular simulation
Publikationen
Project staff
Martin Wendland
Ao.Univ.Prof. Dipl.-Ing. Dr. Martin Wendland
martin.wendland@boku.ac.at
Tel: +43 1 47654-89352
Project Leader
01.11.2012 - 31.10.2014
BOKU partners
External partners
Vienna University, Faculty for Physics
Herwig Peterlik
partner