  We have established the detailed phase diagram of the prototypical deep
eutectic solvent ethaline (ethylene glycol / choline chloride 2:1) as a
function of the hydration level, in the bulk state and confined in the
nanochannels of mesostructured porous silica matrices MCM-41 and SBA-15, with
pore radii $R_P$ = 1.8 nm and 4.15 nm. For neat and moderately hydrated DESs,
freezing was avoided and glassforming solutions were formed in all cases. For
mass fraction of water above a threshold value $W_g'\approx30\%$,
crystallization occurred and led to the formation of a maximally-freeze
concentrated DES solution. In this case, extremely deep melting depressions
were attained in the confined states, due to the combination of confinement and
cryoscopic effects. These phenomena were analyzed quantitatively, based on an
extended version of the classical Gibbs-Thomson and Raoult thermodynamic
approaches. In this framework, the predicted values of the water chemical
activity in the confined systems were shown to systematically deviate from
those of the bulk counterparts. The origin of this striking observation is
discussed with respect to thermodynamic anomalies of water in the 'no-man's
land' and to the probable existence of specific nanostructures in DES solutions
when manipulated in nanochannels or at interfaces with solids.
