A matter of flow

Access through your institution Buy or subscribe These latter peculiarities of confined water occupy the focus of a recent short review (M. Trushin et al. Nat. Rev. Phys. 7, 502–513; 2025). The authors emphasize both the breadth of physical behaviour that water presents and the deep intellectual challenge posed by geometric confinement, which forces theory to dwell in the uncomfortable gap between descriptions based on individual molecular interactions and continuum fluid mechanics. Yet confinement also offers technological opportunities, as low-dimensional water could enable the realization of smart membranes for efficient and ultra-fast desalination, or targeted drug-delivery systems that mimic the efficiency of biological protein channels.As the authors point out, viscosity is a useful measure reflecting the wide variation in behaviour that water exhibits across different environments. At one end of this spectrum, water vapour presents a low viscosity of about 10−5 Pa-s, which is not surprising given that free molecules in the gas move with no impediment. Curiously, water confined to one dimension — as single-file chains in nanotubes — exhibits a similarly low, or only slightly higher, viscosity. Here, molecules form a dipole chain and experience minimal internal friction because the molecules cannot move past one another. At the opposite extreme is solid ice, where a rigid tetrahedral network of hydrogen bonds locks molecules in place, resulting in a viscosity roughly seventeen orders of magnitude higher than that of vapour. In between, various other phases possess intermediate viscosities. This is a preview of subscription content, access via your institution Access options Access through your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any time Learn more Subscribe to this journal Receive 12 print issues and online access $259.00 per year only $21.58 per issue Learn more Buy this articlePurchase on SpringerLinkInstant access to the full article PDF.USD 39.95Prices may be subject to local taxes which are calculated during checkout Author informationAuthors and AffiliationsNature Physics https://www.nature.com/naturephysicsMark BuchananAuthorsMark BuchananView author publicationsSearch author on:PubMed Google ScholarCorresponding authorCorrespondence to Mark Buchanan.Rights and permissionsReprints and permissionsAbout this articleCite this articleBuchanan, M. A matter of flow. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03212-8Download citationPublished: 16 March 2026Version of record: 16 March 2026DOI: https://doi.org/10.1038/s41567-026-03212-8Share this articleAnyone you share the following link with will be able to read this content:Get shareable linkSorry, a shareable link is not currently available for this article.Copy shareable link to clipboard Provided by the Springer Nature SharedIt content-sharing initiative