Supersolid Skin Mechanics of Water and Ice

Abstract

Skins of water and ice perform anomalously in capacities of hydrophobicity, lubricity, mass density, thermal stability, viscoelasticity, and phonon frequency with yet little knowledge about the mechanism behind these anomalies. We present the recent progress in this regard from the perspective of molecular undercoordination induced O:H-O bond segmental cooperative relaxation and nonbonding electron polarization. The skin molecular undercoordination shortens the intramolecular H-O covalent bond spontaneously from 1.0 to 0.84 Ǻ, while the Coulomb repulsion between oxygen anions lengthens the intermolecular O:H nonbond from 1.70 to 2.71 Ǻ associated with strong polarization. The O:H-O resultant elongation depresses the mass density to 0.75 g/cm³; the polarization results the skin high stress, hydrophobicity, lubricity, viscoelasticity; the H-O contraction shifts its stretching vibration frequency from the bulk value of 3150 to 3450 cm^-1 at skin and to 3650 cm^-1 of vapor; the O:H elongation shifts its stretching mode from 210 of bulk to 180 cm^-1 at skin. Therefore, molecular undercoordination induced O:H-O bond relaxation and the associated polarization govern the performance of molecules at the skins of water and ice.