A liquid film motor

Abstract

It is well known that electro-hydrodynamical effects in freely suspended liquid films can force liquids to flow. Here, we report a purely electrically driven rotation in water and some other liquid suspended films with full control on the velocity and the chirality of the rotating vortices. The device, which is called ''film motor'', consists of a quasi two-dimensional electrolysis cell in an external in-plane electric field, crossing the mean electrolysis current density. If either the external field or the electrolysis voltage exceeds some threshold (while the other does not vanish), the liquid film begins to rotate. The device works perfectly with both DC and AC fields.

Liquid bulk rotation induced by electric field at free surface

“…For a suspended film of liquid, which was called a liquid film motor, 19,20 the same results were reported. When the free surface of the polar liquid is covered with a nonpolar thin film, the rotation dies.…”

“…Amjadi et al have shown that applying a uniform electric field to a water film (soap solution), which possesses a uniform electric current, produces a controllable rotating flow in the film. 19,20 The controllable rotation of a fluid film has also been reported for polar liquid films 19,20 and MBBA liquid crystal films. 21 In all of these cases, the rotation of a thin suspended film of fluid was studied.…”

“…This observation is in agreement with the previous experimental and theoretical studies on the rotation of a suspended film of liquid. 19,20,25,26 From Fig. 4, one can conclude that the angular velocity is independent of the concentration of NaCl.…”

“…These techniques are based on the use of thermal gradients, 12,13 magnetic fields, 14,15 or electromechanical means such as piezoelectric actuators. 16 Many such experiments require fluid rotation 10,17,18 that itself requires mechanisms such as using AC and DC electric fields [19][20][21] or a magnetic field and a magnetic probe 17 to rotate a thin liquid film. A polar fluid, connected to a low DC voltage and high electric field, experiences a torque caused by the electric field maintenance of the equilibrium in polarization.…”

Rotation induced by uniform and non-uniform magnetic fields in a conducting fluid carrying an electric current

“…Morris et al 15,16 suggested that it is the electric charges accumulated on the surface of suspended lms that produce such instabilities. Amjadi et al [17][18][19] proposed a method for controlling the rotational ow on thin suspended liquid lms demonstrating that a simultaneous application of an electric eld and an electric current produces controllable rotations in a suspended liquid lm. Such an instability has been studied theoretically by Liu et al 20,21 and Nasiri et al 22 and the rotation mechanism was explained by Feiz et al using a thin lm electro-convection model.…”