Effect of Geometry on Particle Adhesion

Abstract

Forces between solids in air are predominantly attractive and cause adhesion of particles to each other and to surfaces. These forces become increasingly difficult for fine particles to overcome because the particle mass varies to the third power of the particle size. Very high accelerations are therefore required for particle deagglomeration or removal from surfaces.

The particle adhesion phenomenon is important in a variety of scientific and engineering applications. Agglomeration, resulting from particle adhesion, affects the particle-size distribution and physical properties of aerosols and other particulate systems. In powders, tensile and shear strengths are determined by interparticle forces and they influence properties such as the dispersibility of powders in fluids and flow-through bins and hoppers. Effective particle removal by filtration depends on the ability of particles to remain on the collector surface.

The objective of this study was to investigate the role of particle geometry on adhesion and to develop a technique for rapid and accurate particle adhesion measurement. An ultrasonic vibration technique, in conjunction with an optical particle counter, was used to measure the adhesion forces for flat, cylindrical, and spherical particles of two materials and glass deposited on a similar substrate in a dry, static-free environment. Current models for calculation of adhesive forces between a sphere and flat substrate have previously been tested in numerous experimental studies. However, few data exist for the adhesion forces between flat or cylindrical particles and a flat substrate.

The results are compared to the simple adhesion models (based on the van der Waals forces only) for the three geometries. Once the Hamaker constant for a material is known from experiments conducted with spherical particles, the force of adhesion for known particles of other geometries should be predictable. However, the actual contact are of a loosely bound particle is made up of a large number of unknown surface asperities, making the actual adhesion force far less predictable.