Nafion: A Flexible Template for Selective Structuring.

The peculiarities of crystal growth on a Nafion polymeric substrate from supersaturated aqueous solutions of initial substances were studied. The solutions were prepared based on deionized natural water and deuterium-depleted water. As was found earlier, in natural water (deuterium content 157 ± 1 ppm) polymer fibers are capable of unwinding towards the bulk of the liquid, while in deuterium-depleted water (deuterium content ≤ 3 ppm) there is no such effect. Since the distance between the unwound fibers falls in a nanometer range (which is close to the size of the unit cell of the crystal lattice), and these fibers are directed normally to the polymeric substrate, the unwinding can affect crystal growth on the polymer substrate. As was obtained in experiments with X-ray diffractometry, the unwound polymer fibers predetermine syngony of crystals, for which the unit cell is either a rectangular parallelepiped (monoclinic system) or an oblique parallelepiped (triclinic system). A quantitative theoretical model that describes the local interaction of the polymer substrate with the crystalline complexes is presented. Within this model, the polymer substrate can be considered as a flexible matrix for growing crystals.

Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na+: Nonempirical Insight.

The stationary nonempirical simulations of [Na(H2O)n]+ clusters with n in the range of 28-51 carried out at the density functional level with a hybrid B3LYP functional and the Born-Oppenheimer molecular dynamics modeling of the size-selected clusters reveal the interrelated structural and energetic peculiarities of the sodium ion hydration structures. Surface, bulk, and transient structures are distinguished by different locations of the sodium nucleus (close to either the spatial center of the structure or one of its side faces) and a consistently changing coordination number (which typically equals five or six). The differences and correlations between the stationary and averaged dynamically changing configurations are quantified. The ⟨rNaO⟩, mean Na-O distances for the first-shell water molecules, are found to depend both on the spatial character of the structure and the local coordination of sodium. The ⟨rNaO⟩ values are compared to different experimental estimates, and the virtual discrepancy of the latter is explained based on the results of cluster simulations. Different coordination neighborhoods of the sodium ion are predicted depending on its local fraction in actual specimens.