In the relentless quest to ensure access to clean and safe water, membranes endowed with nanometre- and subnanometre-scale pores have emerged as technological cornerstones. Operating at scales so microscopic that they border on the atomic, these membranes enable water purification techniques vital to desalination, wastewater reuse, resource recovery, and the burgeoning field of green hydrogen production. Yet, despite their transformative impact, the molecular intricacies of how water and ions traverse these ultrathin barriers have remained shrouded in uncertainty. A groundbreaking Perspective article authored by Fan, Parkinson, Agrawal, and colleagues published in Nature Water (2026) offers a compelling multiscale framework that promises to revolutionize our understanding of transport mechanisms in these essential membranes, bridging macroscopic engineering models with atomistic insights.
At the heart of this Perspective lies a critical evaluation of the classical macroscopic models that have long governed membrane science. Traditional continuum theories treat membrane transport through broad simplifications—portrayals that often assume homogeneous pore structures and idealized flow behaviors. Yet, as water and ion channels descend into nanoscopic and angstrom-level dimensions, these assumptions begin to falter. The authors expose inherent limitations in these approaches, demonstrating that they cannot fully encapsulate the complex, heterogeneous environments encountered within advanced polymeric membranes. This critical recognition challenges decades of conventional wisdom and sets the stage for a more nuanced understanding of molecular transport.
Delving deeper, the article shines light on revelations from nano- and ångström-scale fluidic studies that capture phenomena defying classical expectations. At these tiny scales, water does not behave as an ordinary liquid; it exhibits anomalous flow characteristics, including near-frictionless slip, altered dielectric properties, and discrete ion hydration dynamics that dramatically influence permeation. These unconventional behaviours underscore the need to transcend continuum assumptions, embracing instead a paradigm that accounts for molecular discreteness, confinement effects, and fluctuating interfacial forces. This shift pushes the boundaries of fluid mechanics into realms traditionally dominated by physics and chemistry.
Complementing these experimental insights, molecular simulations emerge as powerful tools unlocking atomistic resolutions of membrane transport that were previously unobtainable. By simulating the intricate dance of water molecules and ions as they navigate the labyrinthine network of pores and polymer chains, researchers can probe how dynamic heterogeneity within membranes modulates permeability and selectivity. This molecular choreography reveals subtle interactions such as transient hydrogen bonding, steric hindrances, and ion dehydration processes crucial for understanding filtration efficiency and rejection characteristics. Consequently, simulations become indispensable in visualizing and quantifying transport phenomena inaccessible to conventional experimental probes.
Yet, understanding molecular-scale behaviour alone cannot suffice. The authors champion the necessity of integrating insights across hierarchical scales—from molecular to microscopic to macroscopic—to frame a comprehensive mechanistic narrative. Such an integrative approach can reconcile atomistic findings with bulk transport properties, enabling predictive membrane design grounded in fundamental physics. This multiscale paradigm facilitates the translation of molecular understanding into actionable engineering principles assisting membrane fabrication, optimization, and real-world deployment.
This Perspective further illuminates the challenges confronting membrane researchers today, identifying critical knowledge gaps that impede progress. How do transient pore geometries and polymer segmental dynamics contribute to observed transport anomalies? What fundamental principles govern ion-specific selectivity in such confined geometries under varying chemical and electrical conditions? Addressing these questions requires advanced characterization methods capable of operando nanoscale resolution, coupled with multiscale modeling frameworks reconciling disparate data modalities. Such endeavors demand collaborative efforts across disciplines encompassing materials science, physics, computational chemistry, and chemical engineering.
The authors also highlight exciting emerging opportunities poised to accelerate breakthroughs. Advances in high-resolution spectroscopy and microscopy techniques, including cryo-electron tomography and in situ atomic force microscopy, now allow unprecedented visualization of hydrated polymer networks’ structural dynamics. Concurrently, machine learning-driven molecular simulations promise to scale up atomistic insights, enabling accurate predictions of membrane performance under realistic operational scenarios. Integrating these innovations with classical transport theories paves a promising path toward rational design of next-generation membranes boasting enhanced flux, durability, and ion selectivity.
An especially intriguing outcome of this multiscale framework is its potential impact on green hydrogen production, where selective proton transport and water purification are pivotal. By dissecting the atomistic mechanisms governing proton and ion movement through complex polymeric matrices, the new insights could enable membranes finely tuned for energy-efficient electrolyzers and fuel cell technologies. Similarly, in desalination and wastewater reuse, overcoming limitations imposed by imperfect membrane selectivity and fouling phenomena through an improved mechanistic understanding could drastically reduce energy consumption and increase process robustness, supporting sustainable water management goals globally.
In validating their framework, the authors enumerate case studies demonstrating how integrating multiscale data yields unprecedented predictive capability. By reconciling discrepancies between macroscopic permeability measurements and molecular-level transport paths, these studies underscore the synergy achievable when combining continuum modeling, nanochannel experiments, and atomistic simulations. The resulting models account for membrane heterogeneity, realistic pore geometries, and dynamic polymer motion, transcending simplistic assumptions that have hindered predictive accuracy in the past.
Importantly, the Perspective recognizes that membranes operate as dynamic, nonequilibrium systems subject to complex external stimuli such as pressure gradients, electric fields, and concentration variations. Capturing the interplay between these driving forces and intrinsic molecular processes is essential for a faithful depiction of transport phenomena. The authors advocate for theoretical frameworks embracing these factors, including stochastic approaches and non-equilibrium molecular dynamics simulations that can describe transient responses and fluctuating transport rates in realistic settings.
As researchers endeavor to bridge scales from angstroms to centimeters, collaborative, interdisciplinary research models emerge as a prerequisite. Material scientists, computational experts, chemists, and process engineers must align goals and share insights to construct comprehensive models enriched by diverse perspectives. Such collective efforts can accelerate the translation of multiscale understanding into tangible membrane innovations, enabling the development of materials tailored at the molecular level for targeted performance metrics.
In conclusion, this Perspective heralds a paradigm shift in membrane science, moving beyond fragmented views toward a cohesive multiscale understanding of transport mechanisms. By elucidating molecular phenomena underpinning macroscopic performance, it equips the scientific community with a robust mechanistic toolbox vital for designing the membranes of tomorrow. As global water scarcity intensifies and sustainable energy demands grow, such transformative frameworks will be instrumental in meeting pressing environmental challenges with technological elegance and efficacy.
The integration of experimental discoveries, computational advancements, and theoretical refinements illustrated in this work exemplifies a broader trend toward convergence science—where boundaries between disciplines dissolve to solve complex problems holistically. In doing so, this Perspective not only redefines membrane research but also sets a compelling example for other fields grappling with multiscale complexity, from catalysis to biomolecular engineering. The future of membrane-enabled aqueous separations thus shines brightly, illuminated by insights into the molecular currents flowing within.
Subject of Research: Transport mechanisms in desalination and ion-selective membranes across multiple length scales.
Article Title: A multiscale perspective for understanding transport mechanisms in desalination and ion-selective membranes.
Article References:
Fan, H., Parkinson, M., Agrawal, K.V. et al. A multiscale perspective for understanding transport mechanisms in desalination and ion-selective membranes. Nat Water (2026). https://doi.org/10.1038/s44221-026-00585-1
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s44221-026-00585-1
