The adhesion of irregularly-shaped 8 mu m diameter particles to substrates: The contributions of electrostatic and van der Waals interactions

The forces needed to remove irregularly-shaped. 8 mum diameter, polyester p articles from a polyester substrate were measured using an ultracentrifuge. Measurements were also made on a second set of similar particles where nan ometer-size silica clusters had been placed on their surfaces. These silica clusters acted as spacers, reducing direct contact between the particle an d the substrate. It was found that the separation forces for the bare parti cles were consistent with predictions of the JKR theory of adhesion, but we re much larger than could be accounted For from simple electrostatic intera ctions associated with either uniformly-charged particles or particles with localized charged parches. It was found, however, that the forces needed r o effect separation decreased with increasing silica concentration. For par ticles with 2% by weight silica clusters on their surfaces, the separation force was only about 5% of the separation forces of the bare particles. At this concentration of silica, the estimates of the separation forces obtain ed from JKR theory, from the uniformly-charged model, and From the localize d-charged-patch model are all about equal. The numerical estimates are cons istent with the experimentally-obtained values.