Microscopic engine powered by critical demixing

Master's thesis

Falko Schmidt

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Schmidt, F. (2016). Microscopic engine powered by critical demixing (Master's thesis).

Schmidt, Falko. “Microscopic Engine Powered by Critical Demixing,” 2016.

Schmidt, Falko. Microscopic Engine Powered by Critical Demixing. 2016.

By converting energy into mechanical work, engines play a major role in natural and industrial processes. Moreover, due to the current developments in nanoscience and nan- otechnology, micron-sized engines have been attracting an increasing interest in the scientific community. On the one hand, there have been studies to understand the working principles of molecular motors. On the other hand, several approaches have been tried to realize microscopic artificial engines that are powered, e.g. by the transfer of angular momentum of light, by external magnetic fields, by chemical reactions or by the heat transfer from hot to cold reservoirs in miniaturized versions of macroscopic heat engines. In this thesis, another experimental approach to the realization of a microscopic engine is demonstrated. The proposed engine is powered by the local reversible demixing of a critical binary mixture. In particular, when a microscopic bead is optically trapped by a focused laser beam inside a critical mixture, a diffusiophoretic force emerges, setting the bead into rota- tional motion around the optical axis. This revolutionary behaviour can be tuned by adjusting the optical power, the temperature and the criticality of the mixture. Due to its simple setup and tunability, this mechanism provides a new tool to power micro- and nanodevices with possible applica- tions in biological systems, which might already be at work within cellular membranes. This thesis will provide a thor- ough explanation of this engine’s working principle as well as quantitative discussions about its properties, while putting it into context with already proposed artificial microscopic engines, and finally presents first ideas of its integration into future nanomachines.
Microscopic particles are trapped inside the focus of a laser beam around which they start rotating.