Water becomes a supercooled complex fluid below freezing temperatures under isochoric conditions

Cooling water below 0 ∘ C under constant volume (isochoric) conditions is experimentally straightforward. However, we found that the dynamic response of the constrained cooled liquid is far from trivial. First, after a slight supercooled state, normal ice (Ih) forms heterogeneously on the walls of the container, causing, as a result of its inherent expansion, a sudden increase in pressure. Second, being a fragile and brittle solid, the formed ice cannot withstand such pressure and breaks into countless fragments of varying sizes, some of them colloidal ones. Third, as it cools further, bulk water enters a second supercooled state, becomes denser, and eventually forms Ice III. The dynamics of these fascinating behaviors were analyzed by conducting joint thermodynamic and optical experiments based on coherent-gated light scattering. • Two supercooled states appear in pure water under isochoric cooling. • Ice Ih disintegrates due to the internal pressure that builds up during isochoric cooling. • Ice III forms by cooling water under isochoric conditions.