Ultra-Low Density Yet High Elasticity

Molecular volume expands at sites of molecular with fewer than four neighbors. If one considers the shortest distance of 2.70 A [14] and the longest 2.965 A [13] of measurements, the surface doo expands by up to 10 %. Furthermore, the volume of water molecules confined in 5.1 and 2.8 nm Ti02 pores increase by 4 and 7.5 %, respectively, with respect to that in the bulk [15]. A 5-10 A thick air gap between water molecules and the hydrophobic surface [16] make water molecules at the interface like free to exhibit skin vibration attributes [17] of 3,450 cm  

Relaxation of the Chemical Bond, Springer Series in Chemical Physics 108, DOI 10.1007/978-981-4585-21-7 J9, Springer Science-l-Business Media Singapore 2014 

Stiopkin et al. [18] found that the strength of interactions of surface water molecules is distinctly different in structure from the rest of the liquid, and that the water surface has the thickness of just one layer of molecules, which is about 0.3 nm. The surface does not have a long-range impact on water. The timescale for H-bond switching dynamics at the surface is about three times slower than that in the bulk [19] because of the strong polarization induced viscosity. Vibrational sum frequency spectroscopy (VSFS) and MD simulations [20] suggested that the upper most two layers of water molecules are ordered ice like with specific frequency of 3,217 cm at the air/water interface. The density of water molecules is higher in the second layer than the first. 

The density of supersolid phase is indeed lower. In these supersolid regions, molecular under-coordination shortens the and lengthens the Jl, resulting in doo expansion and polarization because of the inter electron-pair repulsion [21]. The least density of ice is 0.92, which corresponds to doo — 2.695(0.92) = 2.7710 A. However, the density of the supersolid phase is p = (2.695/ 2.965) = 0.7509 g cm , which is far below the least density of the bulk ice or the maximal density of water (0.75/0.92/1.0). 

The supersolid skin contains molecules upto two layers. A comparative study using x-ray and neutron scattering, sum-frequency vibrational spectroscopy and calorimetric measurements of the interaction between water and hydrophobic surface, as well as molecular-statistical calculations of the state of water molecules in the skin prove that the boundary water layer in the vicinity of hydrophobic surface consists of a thin ( 0.5 nm) depletion layer. The density is as low as 0.4 g/cm (correspond to doo = 3.66 A) and a considerable amount (25-30 %) of water molecules with free OH groups, which is characterized by a more ordered network of H-bonds compared to liquid water [22, 23]. 

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