An analog of Friedel oscillations in nanoconfined water

Water confined in nanochannels with localized perturbations exhibits Friedel-like density oscillations that can repel ions from the channels with their long-range force, with implication for applications in ionic sensing and seawater desalination. Water confined in nanometer-scale crevices and cavities underpins a wide range of fundamental processes, such as capillary flow, ion transport and protein folding. However, how water responds within these confined spaces, with prevalent inhomogeneity built in or caused by impurities, is not well understood. Here, we show theoretically that water confined in one-dimensional nanochannels with localized perturbation exhibits pronounced density oscillations. The oscillations occur vividly like the Friedel oscillations in electron density resulting from defects in metals. A model analysis reveals that the density oscillations result from the perturbation-induced molecular scattering that is augmented by the confinement-enhanced correlation of water dipoles. This renders the oscillations a general behavior independent of the channel geometries and specific forms of the perturbation. Under confinements comparable to biological ion channels, such oscillations can strikingly extend over 10 nm, resulting in non-trivial effects at large distances that, for example, repel all ions from the channels with their long-range force. These results deepen the understanding of biological functions and inspire new applications in a variety of domains, such as ionic sensing and seawater desalination.

Automated summary

Water confined in nanochannels with localized perturbations exhibits pronounced density oscillations, similar to the Friedel oscillations in metals. These oscillations result from perturbation-induced molecular scattering and confinement-enhanced correlation of water dipoles, and are independent of channel geometries and specific forms of perturbation. The oscillations can have non-trivial effects at large distances, such as repelling all ions from the channels with their long-range force. These findings deepen the understanding of biological functions and have implications for applications in domains such as ionic sensing and seawater desalination.