Ice nucleation by monolayers of aliphatic alcohols

Monolayers of aliphatic long chain alcohols (C_nH_2n+1OH) were found to induce nucleation of ice at temperatures approaching O°C in contrast to water-soluble alcohols which are efficient antifreeze agents. The corresponding fatty acids and alcohols with bulky hydrophobic groups, induce ice nucleation at temperatures lower by as much as 12°C. The freezing point induced by the amphiphilic alcohols was found to be sensitive not only to area per molecule but also to chain length and parity, reaching higher temperatures for monolayers with n odd. Grazing incidence X-ray diffraction studies performed on some of these alcohols at the air/water interface (at 5°C and at zero pressure), demonstrated the formation of crystalline two-dimensional clusters with a distorted hexagonal cell whose dimensions resemble those of hexagonal ice. The catalysis of ice nucleation by these alcohol monolayers may be rationalized in terms of the structural match between the monolayer domains and the ab layer of hexagonal ice.