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


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 ∆ρt/w where 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.

Original Publication Citation

J. M. Carballo, Q. Ni, J. Vasques, and N. B. Crane, “Controlled Manipulation of Floating Objects on Deformed Fluid Interfaces and Conditions for Stable Equilibria,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, V 512 p118-128, January 1, 2017.

Document Type

Peer-Reviewed Article

Publication Date


Permanent URL


Colloids and Surfaces A: Physicochemical and Engineering Aspects




Ira A. Fulton College of Engineering and Technology


Mechanical Engineering

University Standing at Time of Publication

Full Professor