Faraday instabilities leading to electrochemomechanical generation of sub-μA AC upon application of DC voltage across freestanding oil–water interfaces

Abstract

In this article, we report the generation of alternating current by the application of constant and ramping DC voltages across oil–water interfaces. The work reported here can be broadly divided into two parts depending on the shapes of oil–water interfaces, i.e., flattened and curved. In the first part, an alternating current of ∼100 nA (amplitude) was generated by applying a constant DC voltage of −3 V and above across a freestanding and flattened oil–water interface. In another part, an alternating current of ∼150 nA (amplitude) was generated by applying a ramping up DC voltage starting from −5 V to 5 V, then again ramping back down to −5 V for the freestanding and curved interface. The suggested qualitative mechanism that engenders such a phenomenon includes the oil–water interface acting like a membrane. This membrane oscillates due to the electrophoretic movement of ions present in the aqueous phase by the application of a DC voltage across the interface. This electrophoretic movement of ions across oil–water interfaces causes Faraday instabilities leading to oscillations of the said interface. This method could also be used to study the stress levels in the interfacial films between two immiscible liquids. It explores the more-than-Moore’s paradigm by finding a substitute to a conventional alternator/inverter that generates alternating current upon applying a DC voltage input. This work would be of substantial interest to researchers exploring alternatives to conventional AC generators that can be used in liquid environments and in the design of novel integrated circuits that could be used for unconventional computing applications.

Effect of depth ratio on Faraday instability in a binary liquid system

“…Such a pattern-forming system (Faraday waves) has been first observed in classic experiments of Faraday (1831) in 1831. The motion of the unstable interface can be used in many applications, such as in the measurement of interfacial tension (Lau et al 2020), and the generation of sub-micro-Ampere current (Kushagra et al 2020). Faraday instability may be employed for forming patterns to create new materials with unique properties (Chen et al 2018) or to make microstructure materials with a high surface area-to-volume ratio (Li et al 2007) in the field of material science.…”

“…Ubal et al (2003) neglected the motion of the upper fluid layer in their numerical simulation study. However, in many applications, it has been seen that the motion of both fluids is important, especially with fluid pairs of comparable densities (Briard et al 2020, Kushagra et al 2020, Bestehorn et al 2021. The unstable interface profile is defined by mode (m, n) (discussed in section 3.1).…”