Monticellite and tephroite commonly show prominent pyramidal faces.
The AFGP molecules are preferentially adsorbed on the prismatic and pyramidal faces of the ice crystals and prevent the growth of these faces due to the pinning effect.
Consequently, the preferential adsorption of AFGP molecules on the prismatic and pyramidal faces might produce the opposite effects of the inhibition and promotion of growth.
The illustration inside the figure shows the anisotropic adsorption states of the AFGP molecules between the basal and other (prismatic and pyramidal) faces.
Molecular dynamics simulation28 also indicated that molecules with an α-helix conformation can be absorbed selectively on the prismatic or pyramidal faces of ice crystals.
When all of the basal and prismatic faces on an ice crystal disappear, the ice crystals should be surrounded by only pyramidal faces, which have the slowest growth rate, and finally the formation of a dodecahedral ice particle is complete.
Many tiny ice particles with a dodecahedral shape (several tens of micrometers in size) surrounded by only pyramidal faces (as shown at the center in Fig. 4) are observed in the blood of living fishes in this thermal hysteresis region39,40.
From the geometric arrangement of the glass capillary and growing ice crystal, we conclude that the flat interfaces with interference fringes should be the basal faces (namely, the top and bottom basal faces in Fig. 1(b)) and the faces connecting the basal faces should be one prism face and two pyramidal faces.
By contrast, the ice morphology in an AFGP solution changes to a polyhedral shape surrounded by two parallel hexagonal faces (basal faces), six prismatic faces and trapezoidal pyramidal faces connecting the basal and prismatic faces15,26,27 (see the illustration in Fig. 2).
Consequently, the formation of dodecahedral ice particles suggests that the growth rates of the individual faces must maintain the relationship of Vb>Vpri>Vpyr, where Vb, Vpri, and Vpyr are the growth rates for the basal, prismatic and pyramidal faces, respectively (illustration on the right in Fig. 4).
Previously, AFGP molecules were thought to be adsorbed on the prismatic or pyramidal faces but not on the basal faces and to have the ability to smooth the rough interfaces15,27,28,29, which is recognized as a "smoothing transition", in contrast to the well-known effect of the roughening transition by an impurity30,31.
