The physical state of water under extreme confinement can deviate from bulk behavior, yet such effects are typically considered limited to the sub-10 nm regime. Here we report a stable solid-like water phase under ambient conditions in SiO₂ microtubules spanning the submicron–micron scale. The confined water shows pronounced solid-like behavior: it can be sectioned by focused ion beam (FIB) milling and deforms plastically under stress rather than flowing, while maintaining a stable morphology from − 20 to 90 °C and from high vacuum (10⁻⁵ Pa) to atmospheric pressure. ¹H NMR, Raman, and IR spectra indicate strongly restricted molecular dynamics and a modified hydrogen-bonding environment distinct from bulk liquid water and crystalline ice. ¹H NMR quantification and surface-chemistry controls further identify an exceptionally high density of inner-wall silanol (SiOH) groups as the key factor governing formation and stability, with clear pH dependence and reversible transitions. These findings highlight a mesoscale confinement regime dominated by interfacial chemistry.
An et al. (Thu,) studied this question.