The estimation of the true area of contact between microscopic particles and a flat surface in adhesion contact

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Abstract
The true area of contact between pharmaceutical powder particles and flat surfaces of various materials in adhesion contact has been calculated. The centrifuge technique has been used to measure the adhesion force between the particles and the surfaces after application of a defined press-on force, which caused plastic deformation of the surface asperities. It was found that in most cases the true area of contact is less than 15% of the apparent area of contact, and for irregular particles the true area of contact is less than 10% of the apparent area of contact. Principal Component Analysis indicated that there is a strong proportionality between the work of adhesion, the indentation hardness and the surface roughness on one side, and the reduced Young’s modulus at the contact points between the surfaces and the adhesion force measured on the other side. A model equation could be proposed that allows an approximate prediction of the adhesion force from the four physical properties of the materials in contact.