Continuous and First-Order Liquid–Solid Phase Transitions in Two-Dimensional Water
Nan Ma, Xiaorong Zhao, Xiaoying Liang, Weiduo Zhu, Yunxiang Sun, Wenhui Zhao, Xiao Cheng Zeng
Abstract
Understanding the phase behaviors of nanoconfined water is of importance in fundamental physical science and nanofluidic applications. Herein, we perform sub-microsecond to microsecond long molecular-dynamics (MD) simulations to show evidence of continuous and first-order phase transitions of water confined between two smooth walls with width of h = 1.0 nm. At either relatively low lateral pressure (PL ≤ 10 MPa) or relatively high lateral pressure (PL ≥ 400 MPa), the freezing of the confined water undergoes a first-order phase transition and gives rise to bilayer low-density amorphous (BL-LDA) ice and the trilayer puckered high-density ice (TL-pHDI), respectively. Very interestingly, within a moderate range of lateral pressures (100 MPa ≤ PL ≤ 300 MPa), the confined water appears to undergo a continuous phase transition in the isobaric condition to form a new phase, namely, the bilayer and puckered high-density amorphous (BL-pHDA) ice. A similar continuous phase transition behavior has been reported previously in tens of nanoseconds MD simulations of the freezing of BL water into the BL flat rhombic ice within a narrower hydrophobic nanoslit (h = 0.8 nm) and in the isochoric condition at high densities of water (Han et al. Nat. Phys. 2010, 6, 685). Our simulation results on the pressure-dependent continuous and first-order phase transitions of the confined water extend the previous study in a different way and thereby provide new insights into the novel thermodynamic phase behavior of low-dimensional water in nanoscale confinement.