Liquid soap film generates electricity: a suspended liquid film rotating in an external electric field as an electric generator

We have observed that a rotating liquid soap film generates electricity when placed between two non-contact electrodes with a sufficiently large potential difference. In our experiments, suspended liquid film (water + soap film) is formed on the surface of a circular frame, which is forced to rotate in the x-y horizontal plane by a motor. This system is located at the center of two capacitor-like vertical plates to apply an external electric voltage difference in the x-direction. The produced electric current is collected from the liquid film using two conducting electrodes that are separated in the y-direction. We previously reported that a liquid film in an external electric field rotates when an electric current passes through it, naming it the liquid film motor (LFM). In this paper, we report a novel technique, in which a similar device can be used as an electric generator, converting the rotating mechanical energy to electrical energy. The liquid film electric generator (LFEG) is in stark contrast to the LFM, both of which could be designed similarly in very small scales like microscales with different applications. Although the device is comparable to commercial electric motors or electric generators, there is a significant difference in their working principles. Usually in an electric motor or generator, the magnetic field causes the driving force, while in a LFM or LFEG, the Coulomb force is the driving force. This fact is also interesting from the bioscience point of view and brings a similarity to biomotors. Here, we have investigated the electrical characteristics of such a generator for the first time experimentally and modeled the phenomenon with electroconvection governing equations. A numerical simulation is performed using the local approximation for the charge-potential relation, and results are in qualitative agreement with experiments.