Phase Diagram of Hydration Shells in Ionic Solutions

Review: Water at ions, biomolecules and charged surfaces

“…The fact that such a relatively simple approach applied here leads to a number of phenomena at quantitatively correctly predicted physical conditions may be attributed, in our opinion, to two main ingredients. Firstly, the dielectric behavior (permittivity) of water, thought as a hydrogen-bonded substance, is correctly accounted for by applying a simple statistical model, which previously proved its usefulness in describing hydrogen-bonded liquids [12]. Secondly, the striction properties of water are treated realistically by using the compressibility isotherms for H 2 O under high pressure (10 5 Pa to about 100 GPa) in no field [46][47][48], together with an ad hoc hypothesis (checked a posteriori to be true with a very good accuracy [6]), saying that they are only negligibly affected by the field.…”

“…For the fields of the strengths E > 10 9 V m À1 the mean cosine hcos i is > 0.99 [12], which means that very strong electric fields produce a dielectric saturation phenomenon. Models of the dipole orientation contribution and effects of dielectric saturation were already earlier treated in the context of metal-electrolyte interface ( [13], p. 119 therein) and in the context of the hydration shells of ions ( [14], p. 142 therein).…”

“…After [29] with the straight line denoted Onsager(2) added by one of the present authors (cf. [12]). …”

“…The value of the electric field such that the energy of H 2 O dipole moment in this field equals the hydrogen bond energy W HB (cf. [12]) is E ¼ 0.29 Â 10 10 V m À1 , the permittivity in this field is ¼ 11.6, and x ¼ 2.064 Å . The latter value of x lies very close to x ¼ 2.217 Å at about which d À1 begins to drop.…”

“…The first shells of monovalent cations, except Li þ , and the first shells of anions: F À , Cl À , Br À , and I À (formed at reduced distances x > 2.217 Å , cf. [12], Table II therein) belong also to phase B. Water in their shells is not compressed.…”