Heterogeneous Electrofreezing of Super Cooled Water on Surfaces of Pyroelectric Crystals is Trigered by Planar-Trigonal Ions.

Electrofreezing experiments of super-cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO 3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO 3 ⁻ ) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H 3 O ⁺ ), slightly reduces the icing temperature. Molecular dynamic simulations suggest that the hydrated planar-trigonal HCO 3 ⁻ ions self-assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice-like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the planar trigonal ions of NO 3 ⁻ and guanidinium (Gdm ⁺ ) elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl ⁻ and SO 4 2 ⁻ ions of different configurations reduce the icing temperature.