Concentration dependence of cation-induced electrohydrodynamic flow passing through an anion exchange membrane

Abstract

Electrohydrodynamic (EHD) flow is a type of liquid flow driven by an external electric force. In electrolyte solutions, anions and cations usually interact with each other to maintain electroneutrality. Under such a condition, it is difficult to drive a liquid flow by applying electric potentials on the order of 1 V; at least a few tens of volts is required to generate EHD flows, which may not be preferable for aqueous solutions. In this study, we propose a novel method of generating a liquid flow through a channel with cross-sectional dimensions of 1 × 1 mm2, which is placed in an ion exchange membrane to separate the cation and anion transport pathways. When the optimized design of the experimental apparatus was used, EHD flows were successfully generated in aqueous solutions by applying a relatively low electric potential of 2.2 V, and the flow velocity was measured over a wide range of electrolyte concentrations by particle image velocimetry. It was found that high concentration gradients caused the rapid discharge of ions passing through the channel and contributed to achieving a flow speed on the order of 1 mm/s. EHD flows were also theoretically explained using the Navier–Stokes equations to model an ion-drag flow driven by nonequilibrium ion transport in external electric fields. This flow generation method is practical only when ion transport pathways are well controlled and effectively rectified. The present findings will lead to the development of a promising technology to control liquid flows in multiscale fluidic channels.

Development of glass micro-electrodes for local electric field, electrical conductivity, and pH measurements

“…Due to the concentration of the electric lines of force in a narrow channel, an almost uniform electric field is formed in the test section, which is suitable for the www.nature.com/scientificreports www.nature.com/scientificreports/ measurement of the electrical conductivity of electrolyte solutions. Using this method, it is expected that ion concentration fields as well as electric potentials at specific environments, such as interfaces at different size channel connections and near surfaces of ion-exchange membranes where enrichment and depletion occur under ionic current conditions [39][40][41] , are clarified. We will tackle such a challenging topic in the near future.…”

Quantitative Evaluation of Optical Forces by Single Particle Tracking in Slit-like Microfluidic Channels

“…In this study, we carry out observations of single particle transport driven by optical forces in a slit-like microfluidic channel and analyze the behavior by using particle tracking velocimetry (PTV). , Confining the transport in the microchannel makes it easy to focus on the radial component of optical forces. The velocity and acceleration of single particles are expressed as a function of distance from a focal point.…”

Mathematical model of the auditory nerve response to stimulation by a micro‐machined cochlea

“…In the present experimental setup, the feedback system occasionally failed under a relatively small input ratio F in / M ; therefore, the results indicated by open triangles are close to those without feedback. Although the indicated results should be evaluated by applying a stochastic analysis, such as a Smirnov–Grubbs outlier test with 1% (or 5%) significance or the modified Thompson‐ τ method, 44 these analyses were not performed in Figure 7A,C because of the above considerations. However, it can be said that the delay in the feedback signal is acceptable for an appropriate level of control and the piezoelectric device can reproduce the motion expressed by Equation (3).…”

“…With F in / M = 2 × 10 −4 m/s 2 and f in = 1 kHz, the feedback control works to effectively amplify the electrical response of the nerve cell, as shown in (B). The clear spike signals within the duration of 0.1 s are limited to 6 peaks that are less than 1 kHz owing to the spatiotemporal scale of ion transport phenomena in liquids 37,42,45 …”