  The fascinating ability of algae, insects and fishes to survive at
temperatures below normal freezing is realized by antifreeze proteins (AFPs).
These are surface-active molecules and interact with the diffusive water/ice
interface thus preventing complete solidification. We propose a new dynamical
mechanism on how these proteins inhibit the freezing of water. We apply a
Ginzburg-Landau type approach to describe the phase separation in the
two-component system (ice, AFP). The free energy density involves two fields:
one for the ice phase with a low AFP concentration, and one for liquid water
with a high AFP concentration. The time evolution of the ice reveals
microstructures resulting from phase separation in the presence of AFPs. We
observed a faster clustering of pre-ice structure connected to a locking of
grain size by the action of AFP, which is an essentially dynamical process. The
adsorption of additional water molecules is inhibited and the further growth of
ice grains stopped. The interfacial energy between ice and water is lowered
allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis
in magnetic materials we observe a thermodynamic hysteresis leading to a
nonlinear density dependence of the freezing point depression in agreement with
the experiments.
