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Applications of Critical Casimir Forces

Final Report Summary - CRITICALFORCE (Applications of Critical Casimir Forces)

Long-ranged forces between mesoscopic objects emerge when a fluctuating field is confined. Quantum-electro-dynamical (QED) Casimir forces emerge between conducting objects due to the confinement of the vacuum electromagnetic fluctuations. Analogously, critical Casimir forces emerge between microscopic objects due to the confinement of the fluid density fluctuations (i.e. fluctuations in the concentration of the component in a binary liquid mixture). In this project, we have studied experimentally several novel aspects and applications of critical Casimir fluctuations. These forces are a promising candidate to harness forces and interactions at mesoscopic and nanoscopic length-scales and promise to deliver results of both fundamental and applied interest. In particular, we have studied the critical Casimir forces between multiple objects and multiple-body effects focusing ur experimental work on a critical mixture of walter-2,6-lutidine. Thanks to these experiments, we have been able (1) to measure the critical Casimir forces between two colloidal particles in bulk and (2) to demonstrate that critical Casimir forces are non-additive. Both these results were obtained for the first time in the context of this project. The potential socio-economical impact of the research associated to this proposal fits within the current trend towards the development of nanotechnology and nanoscience. The specific aim of the present project has been to provide new tools to harness forces and interactions at mesoscopic and nanoscopic length-scales, e.g. the forces arising between several nanodevices, by gaining a better understanding and by exploring possible applications of critical Casimir forces. Critical Casimir forces are interesting from the fundamental point of view as a manifestation of critical phenomena, but also, and perhaps more importantly, from the technological point of view, e.g. as a tunable mechanism to prevent the sticking in MEMS and NEMS (micro- and nanoelectromechanical systems) due to QED (quantum-electrodynamical) Casimir forces. The experimental study of critical Casimir forces acting on microscopic object is a fairly new field of research, which can benefit from the novel techniques we have deployed within this proposal.