Controlled Manipulation of Floating Objects on Deformed Fluid Interfaces and Conditions for Stable Equilibria

Document Type


Publication Date



capillarity, capillary charge, electrowetting, interfacial assembly, semi-immersed rod

Digital Object Identifier (DOI)



At the millimeter scale, interactions between floating and semi-immersed objects are significant. The local curvature of the interface is modified by the weight/buoyancy forces of floating objects, and by the surface properties of semi-immersed objects. The curvature changes generate attractive (or repulsive) interactions between floating parts, and semi-immersed objects. This work demonstrates how electrowetting can manipulate these interactions in order to position, align, assemble and transport parts attached to the fluid interface. This demonstrates one way in which fluid interfaces can provide an alternative to standard pick and place technology for part positioning/assembly. Typically, the part/rod forces are purely attractive or repulsive, but under some conditions, floating objects reach a stable equilibrium with a finite gap between the floating and semi- immersed bodies. Stable equilibrium positions were measured for rectangular prisms suspended on a water/oil interface and a fixed cylindrical rod. Measurements showed that the equilibrium position depends on the ratio of ▵ρtwwhere t is the part thickness; w is its width, and ▵ρ the part/fluid density difference. The stable equilibrium position provides for repeatable positioning without risk of parts sticking to the semi-immersed bodies.

Was this content written or created while at USF?


Citation / Publisher Attribution

Colloids and Surfaces A: Physicochemical and Engineering Aspects, v. 512, p. 118-128