Large Decrease of Fluctuations for Supercooled Water in Hydrophobic Nanoconfinement

Abstract

Using Monte Carlo simulations we study 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 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% at high P and low temperature T we find a dramatic decrease of compressibility K T , thermal expansion coefficient α P , and specific heat C P . Surprisingly, the effect is present also for c as low as 2.4%. We conclude that even a small presence of nanoscopic hydrophobes can drastically suppress therodynamic fluctuations, making the detection of the LLPT more difficult.

Continuous melting through a hexatic phase in confined bilayer water

“…Computational studies agree that under two-dimensional nanoconfinement water is structured into layers perpendicularly oriented with respect to the confining direction (monolayer [10][11][12][13][14][15][16][17][18], bilayer [19][20][21][22][23][24][25][26][27][28][29], trilayer and so on [30][31][32][33][34]). Most of the computational studies agree with the existence of a stable monolayer square ice phase [10][11][12][13].…”

The principle of minimal episteric distortion of the water matrix and its steering role in protein folding

“…(8). In this section this result is contrasted against thermodynamic data on the spanning of aqueous interfaces with nanoscale detail.…”

“…(6) since it reveals that protein destabilization is commensurate with the thermodynamic cost of creating its interface with water, computed using Eq. (8). This observation prompts us to formulate the principle of MED that should govern conformational changes in the solute that generate concomitant changes in the interface.…”

“…4 The breakdown is attributed to the fact that the bulk-like floppy tetrahedral lattice has been distorted to a point where water is effectively deprived of hydrogen-bond partnerships 6 and tends to preserve its interfacial hydrogen-bond pattern in spite of the field-aligning torque imposed by the electrostatic field. 4 For instance, the complexities of dielectric properties at biological heterogeneous interfaces [8][9][10] bespeak of a spatial scale where the behavior of water dipoles cannot be accounted for through linear polarization relations. 5,[11][12][13] The nanoscale structure of water must be inevitably incorporated into the electrostatic description of "episteric" fields at interfaces that confine the solvent to discrete levels.…”

Supercooling of Water

“…The nucleation of supercooled solutions has been studied for almost 300 years beginning with the early works by Fahrenheit (see Shaw et al 2005). Water has long been known as an unusual liquid and significant research continues today into anomalies such as the compressibility (Abascal and Vega 2011) and the fascinating tendencies when water is confined to nanoscale dimensions (Strekalova et al 2011). High pressure density fluctuations are also an ongoing research area (Mishima 2010), as is the so-called "no man's land", a region of the phase diagram existing below the homogeneous nucleation temperature (~ -38 °C) and above where amorphous ice can be found (~ -118 °C) (Moore and Molinero 2010).…”