Speaker
Prof.
Changqing Sun
(NTU, SIngapore)
Description
We show that transiting NaX/H2O solutions of 0.016 molar concentration (X = F, Cl, Br, I) [1, 2] and NaI/H2O of different concentrations into an ice VI phase and then into an ice VII at 298 K proceeding in different ways. The solute-type-resolved critical pressures PC1 and PC2 increases simultaneously in the Hofmeister series order: X = I > Br > Cl > F 0; comparatively, concentration-resolved PC1 increases faster than the PC2 that remains almost constant at higher NaI/H2O concentration. The PC1 moves along the Liquid-VI phase boundary and merges to PC2 at the Liquid-VI-VII phase junction of 350 K and 3.05 GPa. Observations confirmed that the solute solvation creates electric fields that lengthen and soften the O:H nonbonds and meanwhile shorten and stiffen the H–O bonds [3, 4], being the same to molecular undercoordination [5-7]. Compression, however, does it oppositely [8]. Therefore, compression recovers the electrification-deformed O:H–O bond first and then proceeds to the phase transitions. The concentration-raised anion-anion interaction weakens the electric field within the hydration shell, which discriminates the effect of NaI/H2O concentration from solute types at an identical concentration.
1. Sun, C.Q. and Y. Sun, The Attribute of Water: Single Notion, Multiple Myths. Springer Ser. Chem. Phys. Vol. 113. 2016, Heidelberg: Springer-Verlag. 494 pp.
2. Zeng, Q., et al., Compression icing of room-temperature NaX solutions (X= F, Cl, Br, I). Physical Chemistry Chemical Physics, 2016. 18(20): p. 14046-14054.
3. Zhou, Y., et al., Water molecular structure-order in the NaX hydration shells (X= F, Cl, Br, I). Journal of Molecular Liquids, 2016. 221: p. 788-797.
4. Gong, Y., et al., Raman spectroscopy of alkali halide hydration: hydrogen bond relaxation and polarization. Journal of Raman Spectroscopy, 2016. 47(11): p. 1351–1359.
5. Sun, C.Q., et al., Density, Elasticity, and Stability Anomalies of Water Molecules with Fewer than Four Neighbors. Journal of Physical Chemistry Letters, 2013. 4: p. 2565-2570.
6. Zhang, X., et al., A common supersolid skin covering both water and ice. Physical Chemistry Chemical Physics, 2014. 16(42): p. 22987-22994.
7. Zhang, X., et al., Nanobubble Skin Supersolidity. Langmuir, 2016. 32(43): p. 11321-11327.
8. Sun, C.Q., X. Zhang, and W.T. Zheng, Hidden force opposing ice compression. Chem Sci, 2012. 3: p. 1455-1460.
Significance statement
Salting and compressing have opposite effect on the H-O bond energy that determines the critical pressures for room-temperature liquid-VI-VII phase transition of solutions.
Primary author
Prof.
Changqing Sun
(NTU, SIngapore)
