Surface Phase Transition in Anomalous Fluid in Nanoconfinement

Abstract

We explore by molecular dynamic simulations the thermodynamical behavior of an anomalous fluid confined inside rigid and flexible nanopores. The fluid is modeled by a two length scale potential. In the bulk this system exhibits the density and diffusion anomalous behavior observed in liquid water. We show that the anomalous fluid confined inside rigid and flexible nanopores forms

Influence of disordered porous media on the anomalous properties of a simple water model

“…In order to answer these questions water-like atomistic or continuous effective potential models were explored. The confining geometries could be plates [27][28][29][30][31][32][33][34][35][36][37], one pore [38][39][40][41][42][43][44][45][46], and a disordered matrix [43,52,53,[55][56][57]. The results for the melting temperature obtained within these approaches are controversial, while results for SPC/E water show that the melting temperature for hydrophobic plates is lower than the melting for the unconfined system and higher than for the system confined by hydrophilic walls, for the mW model no difference between the melting temperatures due to the hydrophobicity [47] is found.…”

Relation between boundary slip mechanisms and waterlike fluid behavior

“…An anomalous fluid is characterized by having a maximum in the density versus temperature at fixed pressure and a maximum and a minimum in the diffusion coefficient versus pressure at constant temperature [43][44][45][46][47][48]. Under high confinement, these fluids exhibit additional anomalous behaviors and new phases [49,50]. When an anomalous fluid is nanoconfined the thermodynamic and dynamic properties differ from the properties observed in the bulk [29][30][31]51].…”

“…This is not the case for confined systems. A waterlike fluid forms layers which depend on the film thickness [49,50,[52][53][54][55]. Due to the layering, particles show different behaviors in different layers, which allows for the anomalous flux observed in confined waterlike materials.…”

Enhanced diffusion in finite-size simulations of a fragile diatomic glass former

“…In this work we study finite size effects using molecular dynamics simulations of a simple molecular liquid. We use finite size simulations [22][23][24][25][26][27][28][29][30][31][32] instead of confinement [45][46][47][48][49][50][51][52][53][54][55][56] because finite size simulations have the advantage over confinement to cut off the cooperativity without introducing any confining wall nor modifying the symmetry or the dimensionality of the system, as long as periodic boundary conditions are used. The simplicity of the molecule permits us to access large time scales with aging times larger than the micro-second.…”

“…Previous experiments and simulations using confinement found, depending on the conditions, mostly an increase, but sometimes a decrease of the viscosity with the system size [45][46][47][48][49][50][51][52][53][54][55][56] . However previous finite systems simulations [22][23][24][25][26][27][28][29][30][31][32] found to our knowledge always an increase of the viscosity together with a decrease of the cooperativity when the system size decreases.…”