EPJE Topical Review: how capillarity drives the movement of small objects

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Published on 06 February 2019

Moving around small objects using capillary forces is a phenomenon that has stimulated scientists trying to understand the fundamental mechanisms at play. It is also important for many industrial, technological and analytical processes, for example micro-fluidics, oil and gas displacement, mineral flotation, miniature robot and biomechanics. In this EPJ E topical review article Jianlin Liu and Shanpeng Li present a critical review of capillarity-driven migration in which many examples are presented and explained. The small objects in question are non-deformable objects, such as particles, rods, disks and metal sheets as well as soft objects, such as droplets and bubbles. The authors clarify some misunderstandings on the conventional views on these systems.

Two types of interfaces are taken in consideration: the solid-fluid interface and the fluid-fluid interface. Due to the easily deformable properties of the soft objects and distorted interfacial shapes induced by small objects, a convenient way to obtain the driving force is through the potential energy of the system. The asymmetric factors causing the object migration include the asymmetric configuration of the interface, and the difference between the interfacial tensions. Finally, the author offer an outlook on the potential applications of small object migration.