Abstract
Pull-off forces were measured using the vibration method at 30–50% relative humidity for glass and tin spheres on a variety of substrates. The results were compared with those obtained through the colloidal probe technique. Both methods show good agreement for small particle sizes. Since the vibration method causes sinusoidally alternating stresses, the method yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an increase in the adhesion force through flattening of asperities, which also depend on the surface roughness and the mechanical properties of particle and substrate.Pull-off force measurements with the colloidal probe technique and special attention to the influence of the contact force also show an adhesion force intensification with increasing contact forces depending on the surface roughness. No significant adhesion force intensification caused by increasing contact time to 30s at several contact forces was observed. For theoretical predictions based on van der Waals adhesion, an approach presented by Rabinovich and approximations of plastic micro-asperity flattening were combined.
Highlights
The accuracy of dosing procedures with fine powders in the pharmaceutical industry or the removal of abrasive particles after polishing operations are examples for industrial operations which are significantly inf luenced by adhesion phenomena in particle-wall systems. Such adhesion phenomena can arise from several adhesion mechanisms such as van der Waals adhesion, capillary or electrostatic adhesion forces, whose intensity depends on the topography, the chemical composition of the interacting surfaces, environmental conditions such as relative humidity and temperature, and the stresses between the surfaces in contact in combination with their mechanical properties
The paper presents adhesion force measurements between particles and rough substrates obtained through the vibration method at room temperature and moderate relative humidity between 30% and 50%
We focus on the influence of surface roughness and contact forces on adhesion forces, while taking deformations of micro-asperities through alternating contact forces of the vibration method into account
Summary
The accuracy of dosing procedures with fine powders in the pharmaceutical industry or the removal of abrasive particles after polishing operations are examples for industrial operations which are significantly inf luenced by adhesion phenomena in particle-wall systems. The paper presents adhesion force measurements between particles and rough substrates obtained through the vibration method at room temperature and moderate relative humidity between 30% and 50%. Under these ambient conditions, van der Waals adhesion represents the dominating adhesion mechanism. Pull-off forces between particles and substrate were measured using the vibration method and the colloidal probe technique (Nanoscope 3A, Digital Instruments, USA).
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