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We resolved the O:H-O bond transition from the mode of ordinary water to its hydration in terms of its phonon stiffness (vibration frequency shift Δω), order of fluctuation (line width), and number fraction (phonon abundance), fx(C) = Nhyd/Ntotal. The fx(C) follows fH(C) = 0, fLi(C) ∝ fOH(C) ∝ C, and fBr(C) ∝ 1 - exp(-C/C0) toward saturation with C being the solute concentration. The invariant dfx(C)/dC suggests that the solute forms a constantly sized hydration droplet without responding to interference of other ions because its hydrating H2O dipoles fully screen its electric field. However, the number inadequacy of the highly ordered hydration H2O dipoles partially screens the large Br-. The Br- then interacts repulsively with other Br- anions, which weakens its electric field and the fBr(C) approaches saturation at higher solute concentration. The consistency in the concentration trend of the fLiBr(C), the Jones-Dole viscosity η(C), and the surface stress of LiBr solution clarifies their common origin of ionic polarization. The resultant energy of the solvent H-O exothermic elongation by O: ⇔ :O repulsion and the solute H-O endothermic contraction by bond-order deficiency heats up the LiOH solution. An estimation of at least 0.15 eV (160% of the O:H cohesive energy of 0.1 eV) suggests that the H-O elongation is the main source heating up the solution, while the molecular motion, structure fluctuation, or even evaporation dissipates energy caped at 0.1 eV. [ABSTRACT FROM AUTHOR]

From the perspective of O:H-O bond cooperativity, we analyzed the solute capability of transiting the O:H-O bond from the mode of ordinary water to the hydration state and its consequence on the solution viscosity and surface stress. Phonon spectrometric results suggest that glycine and its N-methyl derivatives strongly affect the surrounding solvent molecules through H ↔ H repulsion and dipolar polarization. The H ↔ H interproton repulsion disrupts the surface stress, and the polarization enhances the solution viscosity.

It has long been puzzling that water nanodroplets undergo simultaneously "supercooling" at freezing and "superheating" at melting. Recent progress (Sun et al. J. Phys. Chem. Lett. 2013, 4, 2565, 3238) enables us to resolve this anomaly from the perspective of hydrogen bond (O:H-O) specific heat disparity. A superposition of the specific heat ηx(T) curves for the H-O bond (x = H) and the O:H nonbond (x = L) defines two intersecting temperatures that form the ice/quasi-solid/liquid phase boundaries. Molecular undercoordination (with fewer than four nearest neighbors in the bulk) stretches the ηH(T) curve by raising the Debye temperature ΘDH through H-O bond shortening and phonon stiffening. The ηH(T) stretching is coupled with the ηL(T) depressing because of the Coulomb repulsion between electron pairs on oxygen ions. The extent of dispersion varies with the size of a droplet that prefers a core-shell structure configuration-the bulk interior and the skin. Understandings may open an effective way of dealing with the thermodynamic behavior of water droplets and bubbles from the perspective of O:H-O bond cooperativity.