On detachment of micron droplets using a centrifugal method

Liquid drops adhering to and dislodging from solid surfaces are of common occurrence in a diverse range of industrial and environmental processes. Although tremendous effort, both experimental and theoretical, has been spent on studying the fundamental mechanisms of particle resuspension, most studies concentrated on solid particles. The detachment behaviour of drops is different from that of solid particles; drops may deform and split into smaller portions during detachment and those studies are lacking in literature, especially for small droplets (in the range of micron size). This paper studies the detachment of a droplet from a plastic substrate by a centrifugal method. Monodisperse glycerol droplets in the sizes of micron ranges were generated and deposited on the substrate. Owing to the small in size, an ultracentrifuge was employed to generate the removal forces, in both normal and tangential directions. The detachment behaviours were found different in different force directions. For the normal direction, larger droplets split into smaller portions during detachment; some portions are detached and the remains form smaller droplets on the substrate. The volume fraction that remained or detached against the removal forces was determined and the result was compared with that of the solid particle. For the tangential direction, the droplet is stationary until a high enough force field is applied at which the whole droplet is detached. The phenomena are explained by the retention force model which was previously employed in a larger drop and this research shows that the same model is potential to be applicable to a small droplet in micron size.