When does nanofluidic memory disappear? Understanding and reinstating memristive behavior of ionic liquids in two-dimensional nanochannels.

Abstract

Nanofluidic memristors rely on ionic transport in confined nanochannels that depends on the history of the applied voltage, producing pinched hysteresis loops. Yet the conditions under which this memory emerges or disappears remain poorly understood. Here, we investigate the role of the solvent in tuning ion-ion correlations and assess the necessity of asymmetric boundary conditions for generating memristive behavior in ångström-scale two-dimensional (2D) nanochannels. With this nanochannel platform, previously shown to yield four distinct loop styles with aqueous electrolytes, we replace water with room-temperature ionic liquids (RTILs) and RTIL/solvent mixtures. Pure EMIM-TFSI exhibits only non-pinched capacitive I-V loops, demonstrating that extreme confinement alone is insufficient to induce ionic memory. Introducing a molecular solvent (such as acetonitrile) or applying compositional asymmetry (salt-concentration gradients) restores pinched hysteresis. These results identify solvent dielectric properties, miscibility, and ion-correlation strength as key control parameters for enabling or suppressing ionic memory in nanochannels, even under strong confinement. Our findings provide both mechanistic insight into ionic memristor behavior and practical methods for controlling hysteresis in nanofluidic devices.