Speaker
Prof.
Jan Swenson
(Chalmers University of Technology)
Description
In this presentation I will give my personal thoughts about
the calorimetric and relaxation behavior of supercooled bulk
water, based mainly on studies of supercooled water and
aqueous solutions in confinements. Such studies show that
confined water lacks a clear calorimetric glass transition and
associated viscosity related structural relaxation process. This
finding is in contrast to most other liquids and indicates that
the dynamics associated with the glass transition of bulk
water involves an exceptionally large volume of cooperatively
rearranging regions at temperatures close to the glass
transition temperature, Tg, due to the completion of an ice-
like tetrahedral network structure close to Tg. In
confinements, where ice formation can be prevented, no
similar structural relaxation process can occur due to the
geometrical restrictions and no Tg is consequently observed.
For confined water-glycerol solutions the glass transition and
its associated structural relaxation can be observed up to a
water concentration of about 90 wt%. At this high water
concentration Tg increases (and the structural relaxation
slows down) with increasing water content, indicating that
the added water has an anti-plasticizing effect on the glycerol
molecules at such a high water concentration, due to the
rigidity of a nearly tetrahedral hydrogen bonded network
structure of water at low temperatures. The results further
predict that Tg of bulk water should be located at an
unexpectedly high temperature, i.e. at least above 190 K.
This further implies that the results from these confinement
studies seem to be in conflict with previous results for glassy
bulk water. Reasons for this apparent conflict and possible
misinterpretations are discussed. Finally, I give my personal
thoughts about the possible liquid-liquid transition of
supercooled water.
