Effects of a polymeric, nonequilibrium "antifreeze" upon ice growth from water

Antifreeze glycopeptides (AFGPs) that adsorb to ice from liquid water solution and prevent ice crystal growth over a range of supercooling are found in the blood of some Antarctic fish. They are polymers with from four to about 52 monomer units. The shortest, with four and five of the repeating units, adsorb at prism-face orientations, (1010), aligned normal to the c-axis. The adsorption plane of the longer ones is (4150) when the concentration in solution is low. This may be the result of the 3% misfit with the ice structure, producing a bond strain that increases with increasing length of adsorbed AFGP. Jogs to an adjacent plane between every five adsorbed units can explain the new orientation. However, the adsorption plane reverts gradually back to (1010) with increasing concentration in solution. This and the effects upon ice growth habit are discussed in terms of the standard conceptual model of the adsorption of polymers at solid surfaces: adsorption of segments of the molecules, with loops and tails projecting into the solution from the interface. In contrast with the shorter AFGPs, the longer ones produce a novel interface instability caused by the adsorption-inhibition of growth, that produces a submicroscopically fibrous growth texture at higher solution concentrations.