title: Measuring adhesion forces in powder collectives by inertial detachment.
abstract: One way of measuring adhesion forces in fine powders is to place the particles on a surface, retract the surface with a high acceleration, and observe their detachment due to their inertia. To induce detachment of micrometer-sized particles, an acceleration in the order of 500,000g is required. We developed a device in which such high acceleration is provided by a Hopkinson bar and measured via laser vibrometry. Using a Hopkinson bar, the fundamental limit of mechanically possible accelerations is reached, since higher values cause material failure. Particle detachment is detected by optical video microscopy. With subsequent automated data evaluation a statistical distribution of adhesion forces is obtained. To validate the method, adhesion forces for ensembles of single polystyrene and silica particles on a polystyrene coated steel surface were measured under ambient conditions. We were able to investigate more than 150 individual particles in one experiment and obtained adhesion values of particles in a diameter range of 3-13 μm. Measured adhesion forces of small particles agreed with values from colloidal probe measurements and theoretical predictions. However, we observe a stronger increase of adhesion for particles with a diameter larger than roughly 7-10 μm. We suggest that this discrepancy is caused by surface roughness and heterogeneity. Large particles adjust and find a stable position on the surface due to their inertia while small particles tend to remain at the position of first contact. The new device will be applicable to study a broad variety of different particle-surface combinations on a routine basis, including strongly cohesive powders like pharmaceutical drugs for treatment of lung diseases.
authors: Max Planck Institute for Polymer Research , 55128 Mainz, Germany.
authors: Stefanie
authors: S
authors: Wanka
authors: Michael
authors: M
authors: Kappl
authors: Markus
authors: M
authors: Wolkenhauer
authors: Hans-Jürgen
authors: HJ
authors: Butt
mesh_terms: D000268:Adhesiveness; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry*; D016062:Porosity; D011208:Powders / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011137:Polystyrenes; D011208:Powders; D012822:Silicon Dioxide