Dynamics of interfacial water

2H NMR Studies on the Dynamics of Pure and Mixed Hydrogen-Bonded Liquids in Confinement

“…The observed differences for the diverse types of confinements may be unexpected because both surfaces enable hydrogen bonds and not only silica pores, but also elastin molecules yield essentially rigid matrices, as the studied temperatures are below the glass transition of this protein [53]. We expect that the different dynamical behaviors are due to the fact that a considerable fraction of solvent molecules, which is not in direct contact with the matrix exists in the silica pores, but not in the elastin matrix at the studied low solvation level, corroborating the above argument, see Section 3.1.1, and simulation results [44,54,55] that liquid dynamics shows an Arrhenius temperature dependence in the immediate vicinity of essentially solid surfaces.…”

“…Brought to you by | MIT Libraries Authenticated Download Date | 5/11/18 5:34 AM particular, based on a kink in 〈T 1,l 〉 and an emerging nonexponentiality of the corresponding SLR step near ~185 K, see Figure 1a, it was conjectured that water at interfaces shows a glass-transition-like dynamic arrest at this temperature and, hence, its α process has a correlation time τ α ≈ 10 2 s, which is much larger than the observed value of ~10 −5 s [10,43,44]. In harmony with this conjecture, a positron annihilation lifetime spectroscopy study observed a glass transition of interfacial water at T g = 190 K [48].…”

“…Detailed analysis of the 2 H SLR behavior led to the conclusion that the intermediate step can be assigned to a solid water fraction, e.g. distorted ice nuclei, emerging in the pore volume at ~223 K [10,43,44]. Thus, liquid and solid fractions of water coexist inside the silica pores below this temperature, although calorimetric studies did not yield evidence for ice formation in such narrow confinement [4,36].…”

“…Correlation times of water reorientation in the liquid fraction were obtained from analysis of the 〈T 1,l 〉 data using a CC spectral density and from fits of the cc 2 m ( ) F t decays with a Kohlrausch function [10,43,44]. Due to the existence of dynamical heterogeneities, it is useful to characterize water reorientation by an appropriate mean correlation time.…”

“…At low temperatures, NMR and DS correlation times well agree and follow an Arrhenius law with an activation energy of E a = 0.5 eV. Interestingly, the crossover in the water dynamics and the emergence of a fraction of solid water occur in the same temperature range 220-230 K. Therefore, it was argued that the change in water dynamics is not related to a LL transition, but rather to a change from bulk-like dynamics to interface-dominated dynamics, which occurs when a solid fraction forms and further reduces the accessible volume for the liquid fraction [10,43,44].…”