Guest-free monolayer clathrate and its coexistence with two-dimensional high-density ice

Jaeil Baia, Charles Angell, Xiao Cheng Zenga

Research output: Contribution to journalArticlepeer-review

89 Scopus citations


Three-dimensional (3D) gas clathrates are ice-like but distinguished from bulk ices by containing polyhedral nano-cages to accommodate small gas molecules. Without space filling by gas molecules, standalone 3D clathrates have not been observed to form in the laboratory, and they appear to be unstable except at negative pressure. Thus far, experimental evidence for guest-free clathrates has only been found in germanium and silicon, although guest-free hydrate clathrates have been found, in recent simulations, able to grow from cold stretched water, if first nucleated. Herein, we report simulation evidence of spontaneous formation of monolayer clathrate ice, with or without gas molecules, within hydrophobic nano-slit at low temperatures. The guest-free monolayer clathrate ice is a low-density ice (LDI) whose geometric pattern is identical to Archimedean 4·82-truncated square tiling, i.e. a mosaic of tetragons and octagons. At large positive pressure, a second phase of 2D monolayer ice, i.e. the puckered square high-density ice (HDI) can form. The triple point of the LDI/liquid/HDI three-phase coexistence resembles that of the ice-Ih/water/ice-III three-phase coexistence. More interestingly, when the LDI is under a strong compression at 200 K, it transforms into the HDI via a liquid intermediate state, the first direct evidence of Ostwald's rule of stages at 2D. The tensile limit of the 2D LDI and water are close to that of bulk ice-Ih and laboratory water.

Original languageEnglish (US)
Pages (from-to)5718-5722
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number13
StatePublished - Mar 30 2010


  • 2D high-density ice
  • 2D low-density ice
  • 2D monolayer ice clathrate
  • Ostwald rule of stages
  • Tensile limit of 2D liquid

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Guest-free monolayer clathrate and its coexistence with two-dimensional high-density ice'. Together they form a unique fingerprint.

Cite this