Tunable critical Casimir forces counteract Casimir-Lifshitz attraction

Casimir forces are normally attractive and cause stiction, that is, static friction preventing surfaces in contact from starting to move. Now, a system exhibiting tunable repulsive critical Casimir forces, relevant for the evelopment of micro- and nanodevices, is demonstrated. In developing micro- and nanodevices, stiction between their parts, that is, static friction preventing surfaces in contact from moving, is a well-known problem. It is caused by the finite-temperature analogue of the quantum electrodynamical Casimir-Lifshitz forces, which are normally attractive. Repulsive Casimir-Lifshitz forces have been realized experimentally, but their reliance on specialized materials severely limits their applicability and prevents their dynamic control. Here we demonstrate that repulsive critical Casimir forces, which emerge in a critical binary liquid mixture upon approaching the critical temperature, can be used to counteract stiction due to Casimir-Lifshitz forces and actively control microscopic and nanoscopic objects with nanometre precision. Our experiment is conducted on a microscopic gold flake suspended above a flat gold-coated substrate immersed in a critical binary liquid mixture. This may stimulate the development of micro- and nanodevices by preventing stiction as well as by providing active control and precise tunability of the forces acting between their constituent parts.