11.1 Wonders of H 2 O Molecular Undercoordination and Salt Hydration
217
to that the Cl
− , Br
− , and I
− ions weaken their surrounding O:H nonbond, known as
water structure breaking [27, 28].
An external electric field in the 10
9 V/m order slows down water molecular motion
and even crystallizes the solution matrix. The field generated by a Na
+ ion acts rather
locally to reorient and even hydrolyze its neighboring water molecules according to
molecular dynamics (MD) computations [29]. A cation can form a stiffener cylindrical volume between the cation and the graphite-oxide (negatively charged) defects
of the adjacent layers in a “(−) ~ (+) ~ (−)” fashion perpendicular to the graphene
sheets. This stiffer hydration volume expands the graphene-oxide interlayer spacing
up to 1.5 nm and the modulated layer separation varies with the type of cations [30,
31]. Strikingly, charge injection in terms of ions separation by salt solvation shares
the same effect of molecular undercoordination on the hydrogen bond (O:H–O or
HB) segmental length and stiffness and the H–O phonon lifetime [32–34].
Salt hydration and water molecular undercoordination have been intensively
investigated using the following multiscale approaches:
(1) Classical continuum thermodynamics [35–37] embraced the dielectrics, diffusivity, surface stress, viscosity, latent heat, entropy, nucleation, and liquid/vapor
phase transition in terms of free energy, though this approach has faced difficulties in dealing with solvation dynamics and the properties of water and
ice.
(2) MD computations and the ultrafast phonon spectroscopies [38–40] are focused
on the spatial and temporal performance of water and solute molecules as well
as the proton and lone pair transportation behavior. Information includes the
phonon relaxation or the molecular residing time at sites surrounding the solute
or under different coordination conditions or perturbations.
(3) Nuclear quantum interactions [41, 42] simulation has enabled visualizing the
concerted quantum tunneling of protons within the water clusters and quantify the impact of zero–point motion on the strength of a single hydrogen bond
at a water/solid interface. An interlay of STM/S and the ab initio path–integral molecular dynamics (PIMD) verifed unambiguously that the sp
3 –orbital
hybridization takes place at 5 K temperature. The proton quantum interaction
elongates the longer part and shortens the shorter part of the O:H–O bond.
(4) O:H–O bond cooperativity [1, 43–45] enables resolution to multiple mysteries
of water and ice. A combination of the Lagrangian mechanics, MD and density
functional theory (DFT) computations with the static phonon spectrometrics has
enabled quantification of O:H–O transition from the mode of ordinary water to
the conditioned states. Obtained information includes the fraction, stiffness,
and fluctuation order transition upon perturbation and their consequence on
the solution viscosity, surface stress, phase boundary dispersity, and the critical
pressure and temperature for phase transition.
However, knowledge insufficiency about the O:H–O bond cooperativity and polarizability [46] has hindered largely the progress in understanding the effect of molecular undercoordination and salt solvation in terms of bonding dynamics, solute capabilities, and inter- and intramolecular interactions. It has been hardly possible to
217
to that the Cl
− , Br
− , and I
− ions weaken their surrounding O:H nonbond, known as
water structure breaking [27, 28].
An external electric field in the 10
9 V/m order slows down water molecular motion
and even crystallizes the solution matrix. The field generated by a Na
+ ion acts rather
locally to reorient and even hydrolyze its neighboring water molecules according to
molecular dynamics (MD) computations [29]. A cation can form a stiffener cylindrical volume between the cation and the graphite-oxide (negatively charged) defects
of the adjacent layers in a “(−) ~ (+) ~ (−)” fashion perpendicular to the graphene
sheets. This stiffer hydration volume expands the graphene-oxide interlayer spacing
up to 1.5 nm and the modulated layer separation varies with the type of cations [30,
31]. Strikingly, charge injection in terms of ions separation by salt solvation shares
the same effect of molecular undercoordination on the hydrogen bond (O:H–O or
HB) segmental length and stiffness and the H–O phonon lifetime [32–34].
Salt hydration and water molecular undercoordination have been intensively
investigated using the following multiscale approaches:
(1) Classical continuum thermodynamics [35–37] embraced the dielectrics, diffusivity, surface stress, viscosity, latent heat, entropy, nucleation, and liquid/vapor
phase transition in terms of free energy, though this approach has faced difficulties in dealing with solvation dynamics and the properties of water and
ice.
(2) MD computations and the ultrafast phonon spectroscopies [38–40] are focused
on the spatial and temporal performance of water and solute molecules as well
as the proton and lone pair transportation behavior. Information includes the
phonon relaxation or the molecular residing time at sites surrounding the solute
or under different coordination conditions or perturbations.
(3) Nuclear quantum interactions [41, 42] simulation has enabled visualizing the
concerted quantum tunneling of protons within the water clusters and quantify the impact of zero–point motion on the strength of a single hydrogen bond
at a water/solid interface. An interlay of STM/S and the ab initio path–integral molecular dynamics (PIMD) verifed unambiguously that the sp
3 –orbital
hybridization takes place at 5 K temperature. The proton quantum interaction
elongates the longer part and shortens the shorter part of the O:H–O bond.
(4) O:H–O bond cooperativity [1, 43–45] enables resolution to multiple mysteries
of water and ice. A combination of the Lagrangian mechanics, MD and density
functional theory (DFT) computations with the static phonon spectrometrics has
enabled quantification of O:H–O transition from the mode of ordinary water to
the conditioned states. Obtained information includes the fraction, stiffness,
and fluctuation order transition upon perturbation and their consequence on
the solution viscosity, surface stress, phase boundary dispersity, and the critical
pressure and temperature for phase transition.
However, knowledge insufficiency about the O:H–O bond cooperativity and polarizability [46] has hindered largely the progress in understanding the effect of molecular undercoordination and salt solvation in terms of bonding dynamics, solute capabilities, and inter- and intramolecular interactions. It has been hardly possible to