Speaker
Prof.
Paola Gallo
(Università di Roma Tre)
Description
In this talk I shall summarize recent results from computer
simulations that address two important issues: how can the
Widom line of water both in the supercritical and in the
supercooled states help to characterize its properties and
how can aqueous solutions and confinement help to shed light
on water properties in the supercooled region.
The Widom line is the line of convergence of the maxima of
the thermodynamic response functions upon approaching a
critical point. The characterization of this line is very
important in water both in the supercooled and in the
supercritical state and it can be found upon approaching
respectively the liquid-liquid and the liquid gas critical
points.
I will analyze the thermodynamic properties of bulk water in
the supercritical region by comparing experimental results
and computer simulation results along the isobars. The lines
connecting the maxima of the thermodynamic response
functions converge upon approaching the critical point to a
single Widom line separating a liquid-like region from a
gas-like region. This Widom line of supercritical water is
connected to the crossover from a liquid-like to a gas-like
behaviour of the transport coefficients [1].
In the supercooled state the experimental determination of
the liquid-liquid critical point can be eased in aqueous
solutions depending on the solute, as computer simulations
show that its position is shifted in the thermodynamic
planes with respect to the bulk [2]. I will characterize the
Widom line in hydrophilic [3], amphiphilic [4] and
hydrophobic [5] aqueous solutions. I will also show that the
Widom line emanating from the LLCP can be connected to
dynamic crossovers in solutions. Dynamics crossovers are
associated to the crossing of the Widom line both for the
Jagla liquid with hard spheres [5] and for the aqueous
solutions of NaCl [6,7] and the results found in solutions
are comparable to those found in the bulk [8]. In
correspondence with the dynamic crossovers I will show that
the two-body entropy [9] also shows a change of behaviour
and the relation that connects the two body entropy and the
relaxation time in the region where Mode Coupling Theory is
valid does not hold any more.
I will finally briefly discuss the connection between a
dynamic crossover and the Widom line also in confinement
[10,11].
[1] P. Gallo, D. Corradini and M. Rovere, submitted (2014).
[2] D. Corradini, M. Rovere and P. Gallo, J. Chem. Phys.
132, 134508 (2010).
[3] D. Corradini and P. Gallo, J. Phys. Chem. B. 115,
14161 (2011).
[4] D. Corradini, Z. Su, H.E. Stanley and P. Gallo, J.
Chem. Phys. 187, 184503 (2012).
[5] D. Corradini, P. Gallo, S.V. Buldyrev and H.E. Stanley,
Phys. Rev. E 85, 051503 (2012).
[6] P. Gallo, D. Corradini and M. Rovere, Mol. Phys, 109,
2069 (2011).
[7] P. Gallo, D. Corradini and M. Rovere, J. Chem. Phys.
139, 204503 (2013).
[8] P. Gallo and M. Rovere, J. Chem. Phys., 137 , 164503
(2012).
[9] P. Gallo and M. Rovere, submitted (2014).
[10] P. Gallo, M. Rovere and S.-H. Chen, J. Phys.: Condens.
Matter 24 064109 (2012).
[11] P. Gallo, M. Rovere and S.-H. Chen J. Phys. Chem. Lett.
1, 729 (2010).
