Solid−liquid critical behavior of water in nanopores

Significance It is commonly believed that the solid−liquid critical point does not exist, because of the famous symmetry argument and the lack of experimental observation so far. However, recently, the intriguing possibility of the critical point has been suggested for strongly confined substances. Here we perform molecular dynamics simulations of water confined in carbon nanotubes and provide unambiguous evidence of the solid−liquid critical point for water in the hydrophobic nanopore: macroscopic solid–liquid phase separation below a critical temperature T c , diverging heat capacity and isothermal compressibility at around T c , and the loci of response function maxima above T c . We also give a molecular level explanation for how liquid water continuously freezes to ice along a thermodynamic path avoiding the first-order phase boundary.