Concluding remarks: Molecular and ion flows through angstrom-scale channels: bridging theory, simulation, and experiment.

Abstract

These concluding remarks report on a Faraday Discussion in which angstrom-scale confinement emerged not as a geometric extension of bulk behaviour but as a qualitatively distinct thermodynamic and kinetic regime, with emerging evidence that some of its anomalies may have quantum origins. Opened by the Spiers Lecture of Prof. Lydéric Bocquet, the Discussion covered four sessions: structure and dynamics of confined molecules; stimuli-responsive transport; molecular and ion sieving; and iontronics and emergent neuromorphic effects. Machine-learning molecular dynamics at first-principles accuracy revealed a sharp three-layer structural transition in confined water and asymmetric solvation of OH^- and H₃O⁺ under hBN confinement. Active transport control has been demonstrated using light, strain, mechanical force, and solvent composition. Across these studies, surface chemistry and confinement consistently act together, emerging as the main determinants of ion selectivity. In iontronics, memristive-like behaviour has been reported across a remarkably broad range of mechanisms and an even wider variety of nanofluidic platforms, suggesting that such responses may be a pervasive feature of ionic systems whenever coupled transport, interfacial dynamics, and memory effects coexist. Reported origins include asymmetric ion-pair kinetics, energy-barrier rectification in funnel channels, confined water-dipole ordering, coupled capacitive-inductive memory effects, asymmetric electrochemical reactions, and other history-dependent ion-gating and interfacial processes. Across all sessions, a broad consensus emerged that progress on the most important open questions in water/ion transport will depend on close interplay between theory and experiment. At the same time, there was a strong sense that nanofluidics has reached a level of maturity that now makes these challenges tractable, reinforcing a broader excitement across the field.