Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement

TL;DR

This study uses Monte Carlo simulations to explore how hydrophobic nanoconfinement affects water's phase behavior, revealing a significant reduction in thermodynamic fluctuations and the challenge of detecting phase transitions under confinement.

Contribution

It demonstrates that hydrophobic nanoconfinement suppresses thermodynamic fluctuations and alters the liquid-liquid phase transition in supercooled water, a novel insight into confined water behavior.

Findings

Decreased compressibility, thermal expansion, and specific heat at high pressure and low temperature.

Presence of a liquid-liquid phase transition line ending in two critical points.

Fluctuation suppression occurs even at low confinement levels (2.4%).

Abstract

We study by Monte Carlo simulations a coarse-grained model of a water layer confined in a fixed disordered matrix of hydrophobic nanoparticles at different particle concentrations c. For c=0 (bulk water) we find a first order liquid-liquid phase transition (LLPT). For c>0 our simulations are consistent with a LLPT line ending in two critical points at low and high pressure P. For c=25% we find a dramatic decrease of compressibility K_T, thermal expansion coefficient \alpha_P, specific heat C_P at high P and low temperature T. Surprisingly, the effect is present also for c as low as 2.4%. We conclude that the higher the confinement, the lower the thermodynamic fluctuations and the more difficult it will be to detect the LLPT.