Gallo, Paola; Rovere, Mauro; Spohr, Eckhard:

Glass transition and layering effects in confined water: a computer simulation study

In: Journal of chemical physics, Jg. 113 (2000) ; Nr. 24, S. 11324–11335
ISSN: 0021-9606, 1089-7690
Zeitschriftenaufsatz / Fach: Chemie
Fakultät für Chemie
Single particle dynamics of water confined in a nanopore is studied through Computer Molecular
Dynamics. The pore is modeled to represent the average properties of a pore of Vycor glass.
Dynamics is analyzed at different hydration levels and upon supercooling. At all hydration levels
and all temperatures investigated a layering effect is observed due to the strong hydrophilicity of the
substrate. The time density correlators show, already at ambient temperature, strong deviations
from the Debye and the stretched exponential behavior. Both on decreasing hydration level and
upon supercooling we find features that can be related to the cage effect typical of a supercooled
liquid undergoing a kinetic glass transition. Nonetheless the behavior predicted by Mode Coupling
Theory can be observed only by carrying out a proper shell analysis of the density correlators.
Water molecules within the first two layers from the substrate are in a glassy state already at
ambient temperature (bound water). The remaining subset of molecules (free water) undergoes a
kinetic glass transition; the relaxation of the density correlators agree with the main predictions of
the theory. From our data we can predict the temperature of structural arrest of free water.