1,721,928 research outputs found
Anomalous dynamics of confined water at low hydration
No full textThe mobility of water molecules confined in a silica pore is studied by computer simulation in the low hydration regime, where most of the molecules reside close to the hydrophilic substrate. A layer analysis of the single particle dynamics of these molecules shows an anomalous diffusion with a sublinear behaviour over a long period. This behaviour is strictly connected to the long time decay of the residence time distribution analogous to water in contact with proteins
Molecular dynamics study of the glass transition in confined water
No full textA molecular dynamics simulation of SPC/E water confined in a Silica pore is presented. The pore has been constructed to reproduce the average properties of a pore of Vycor glass. Due to the confinement and to the presence of a strong hydrophilic surface, the dynamic behaviour of the liquid appears to be strongly dependent on the hydration level. The approach to the glass transition of confined water is investigated on lowering hydration and on supercooling in the framework of Mode Coupling Theories. Ar higher hydrations two quite distinct subsets of water molecules are detectable. Those belonging to the first layer close to the substrate suffer a severe slowing down, while the remaining ones display a scenario typical of supercooled liquids approaching the kinetic glass transition
Studies of water in confinement by experiments and simulations
No full textExperimental and computational studies of the properties of water confined in different environments are reviewed. Particular emphasis is given to thermodynamics and microscopic structure; the diffusional dynamics is also considered. The need for studies of the vibrational dynamics is pointed out
Mode-coupling behavior of a Lennard-Jones binary mixture upon increasing confinement
No full textMolecular dynamics simulations are performed on a Lennard Jones binary mixture confined in off lattice matrices of soft spheres with increasing radius. We focus on dynamics upon supercooling and in particular on testing the mode coupling theory properties of the confined mixture. Parameters of mode coupling theory in going from bulk to weak confinement, and from weak to strong confinement are extracted from simulations and analyzed. We focus on the study of the behavior of the single particle density correlators. We find that the mode coupling theory retains its validity also in the case of strong confinement, with a reduction of range of validity. The role of hopping is discussed in relation with the differences between the results obtained from the diffusion coefficients and the mode coupling theory predictions
Dynamic Crossover in Supercooled Confined Water: Understanding Bulk Properties through Confinement
No full textWe present here molecular dynamics simulations of deeply supercooled SPC/E water confined in a cylindrical pore of MCM-41 silica material By a layer analysis of the tag particle density. correlators, we are able to extract the a-relaxation time of the mobile portion of the confined water. This relaxation time is the same as what can be extracted from neutron scattering experiments. From examination of the temperature-dependent behavior of the relaxation time and the dynamic susceptibility, we locate a dynamic crossover at T = (215 +/- 5) K and a corresponding peak in the specific heat, in agreement with experimental findings in confined water and simulations. of the bulk water. Our study demonstrates that the recent results of the experiments on confined water are extremely relevant for the comprehension of low-temperature bulk properties of water
Supercooled water: A molecular dynamics simulation study with a polarizable potential
No full textThe behaviour of supercooled water in an extended region of the phase diagram, from ambient conditions to negative pressure and low temperatures, is studied by computer simulation employing a polarizable water potential. The structural analysis of the system shows that the polarizable potential chosen well reproduces the water properties even in extreme conditions and allows us to perform a more detailed thermodynamical analysis. In order to infer features of the phase diagram relevant for the explanation of the anomalous behaviour of metastable water, the density dependence of pressure was analyzed to investigate the pathway of the spinodal line with the decreasing temperature. (C) 2006 Elsevier B.V. All rights reserved
- …
