A model for the fragile-to-strong transition in water

A model based on the existence of two different competing local structures in water is described. It is shown that it can explain the transition betwe en fragile and strong behaviour that supercooled water undergoes at around 220 K. The high-temperature behaviour is similar to that observed in standa rd fragile glass formers. The strong behaviour at low temperatures is assoc iated with the existence of a remanent configurational entropy arising from the possibility of locally choosing between the two possible environments.