The electroconvective instability (ECI) in an electrodialysis channel under a strong electric field is studied here. The phenomenon of ECI with extreme depletion (ECI-HD) is reported; that is, the overlapping vortices cause the extreme depletion zone to propagate in the horizontal direction. Using scaling theory and direct numerical simulation, we indicate a series of features under the ECI-HD. The decrease in ion transport rate with voltage in ECI-HD is different from the enhancement in the ECI with moderate depletion (ECI-MD), which results in a unique peak in the voltage-current curve. More importantly, we reveal that the ECI is regulated by a scaling factor consisting of the electric field, hydrodynamic coupling coefficient, and Péclet number. For the ECI-HD, the scaling factor has an opposite effect on the vortex size and overlimiting current as that on the ECI-MD. The extreme depletion zone of the ECI-HD also has an uncommon diffusion self-similar dynamics. These unique scaling laws allow one to establish the quantitative bridge between the ion concentration, electric field, and vortex size by the overlimiting current.

Striking a balance between sensitivity and detection range while ensuring stability under extreme temperatures remains a formidable challenge in the design of flexible pressure sensors. To address this issue, we draw inspiration from the multi-gradient architectures of nature and propose a bottom-up self-assembly strategy. By leveraging a meticulously orchestrated multi-step approach that encompasses electrospinning, sequential freezing, and thermal imidization, we successfully fabricate a polyimide nanofiber/carbon nanotube dual-gradient aerogel with a dynamic stiffness transition from flexible to rigid states. Experimental results highlight notable properties of the dual-gradient aerogel, which exhibits an ultralow density (0.023 g cm⁻³), efficient thermal insulation (28 mW m⁻¹ K⁻¹), and reliable compressibility and fatigue resistance. Moreover, it establishes a favorable equilibrium between sensitivity (156 MPa⁻¹) and an extensive detection range (223 kPa). Notably, the combination of thermal resilience (−196 °C to 533.30 °C) and mechanical stability enables performance that is comparable to, or in some aspects surpasses, that of conventional flexible sensing materials. This dual-gradient aerogel provides both effective thermal insulation and high-precision physiological monitoring under extreme conditions, offering integrated thermal protection and real-time astronaut health assessment in spacesuits.

Ion and water transport by electroconvection continually finds new applications, arousing considerable research interest. This paper is devoted to the important issue of the effects caused by shear flow, as this flow always occurs in various electrochemical applications, such as electrodeposition, electroplating, and electrodialysis. In this paper, the dimensionless Poiseuille-Navier-Stokes and Poisson-Nernst-Planck model is proposed, which contains the buoyancy force induced by ion concentration polarization. The numerical results show that in the existing literature, the Rayleigh-Bénard convection is neglected and the Debye layer effect is overestimated, leading to a large difference between the simulation results and the experimental data. In addition, the chaotic phenomenon of shear flow is discussed in detail based on the proposed model. The main contributions are as follows: (i) There are two distinct instability phenomena, namely, electroconvective instability, caused by the electric force, and Rayleigh-Bénard instability, caused by the buoyancy force. (ii) For electroconvective instability, the fully overlapping vortex structures in the microchannel are obtained numerically for the first time. In addition, the shear sheltering effect is verified numerically. (iii) The effects of the characteristic length and electrohydrodynamic coupling constant on the Rayleigh-Bénard instability are studied. (iv) The transition condition from electroconvective instability to Rayleigh-Bénard instability is investigated. The analysis shows that choosing a characteristic length consistent with the actual structure is a necessary condition for achieving high-precision analysis of fluid behaviors such as the flow pattern. This conclusion provides important guidance for the design and optimization of the concentration microfluidic chip.

Ion and water are transported by electroconvection near permselective membranes, resulting in complex phenomena associated with the flow–fines interaction. Sheltering the flow chaos by the shear flow is a common strategy in plasma fluids and has recently been successfully applied to control ionic fluids. The paper herein reveals the critical selection of shear velocity regarding the fluid from a chaotic to a steady state through numerical and theoretical analyses. For the shear sheltering, the dimensionless Debye length ${\lambda _D}$ with varying channel height is introduced to achieve a comprehensive discussion of the factors and laws affecting the shear vortex state. Based on an analysis of the vortex driving mechanism, the scaling of the slip velocity ${u_s}\sim {(\lambda _D^{ - 1}\Delta {\phi ^4})^{1/3}}$ is recommended as the critical selection factor for the steady and chaotic state under a fixed shear flow velocity, which involves the dimensionless Debye length ${\lambda _D}$ and voltage difference $\Delta \phi $ . Furthermore, for ionic fluid control by shear flow, a critical shear velocity ${U_{HPC}}$ is proposed to distinguish the electroconvective flow from a chaotic state to a steady state. When the shear flow velocity ${U_{HP}} > {U_{HPC}}$ , the shear flow shelters chaos, and the scaling law is also recommended for the regulation of the critical shear flow velocity ${U_{HPC}}$ jointly by ${\lambda _D}$ and $\Delta \phi $ . The analysis is confirmed by direct numerical simulation and existing experimental data (J. Fluid Mech, vol. 813, 2017, pp. 799–823). This work provides a more comprehensive physical insight for shear sheltering and affects the design of electromembrane microfluidics.

We report that an electro-osmotic instability of concentration enrichment in curved geometries for an aqueous electrolyte, as opposed to the well-known one, is initiated exclusively at the enriched interface (anode), rather than at the depleted one (cathode). For this instability, the limitation of an unrealistically high material Peclet number in planar geometry is eliminated by the strong electric field arising from the line charge singularity. In a model setup of concentric circular electrodes, we show by stability analysis, numerical simulation, and experimental visualization that instability occurs at the inner anode, below a critical radius of curvature. The stability criterion is also formulated in terms of a critical electric field and extended to arbitrary (two-dimensional) geometries by conformal mapping. This discovery suggests that transport may be enhanced in processes limited by salt enrichment, such as reverse osmosis, by triggering this instability with needlelike electrodes.