Elucidating the state of interfacial water, especially the hydrogen-bond configurations, is considered to be key for a better understanding of the functions of polymers that are exhibited in the presence of water. Here, an analysis in this direction is conducted for two water-insoluble biocompatible polymers, poly(2-methoxyethyl acrylate) and cyclic(poly(2-methoxyethyl acrylate)), and a non-biocompatible polymer, poly(n-butyl acrylate), by measuring their IR spectra under humidified conditions and by carrying out theoretical calculations on model complex systems. It is found that the OH stretching bands of water are decomposed into four components, and while the higher-frequency components (with peaks at ∼3610 and ∼3540 cm^-1) behave in parallel with the C═O and C-O-C stretching and CH deformation bands of the polymers, the lower-frequency components (with peaks at ∼3430 and ∼3260 cm^-1) become pronounced to a greater extent with increasing humidity. From the theoretical calculations, it is shown that the OH stretching frequency that is distributed from ∼3650 to ∼3200 cm^-1 is correlated to the hydrogen-bond configurations and is mainly controlled by the electric field that is sensed by the vibrating H atom. By combining these observed and calculated results, the configurations of water at the interface of the polymers are discussed.

The solvation structure around the Li⁺ ion in a mixed cyclic/linear carbonate solution, an important factor for the performance of lithium-based rechargeable batteries, is examined by measuring and analyzing the noncoincidence effect observed for the C═O stretching Raman band. This technique has the advantage of perceiving relative distances and orientations of solvent molecules clustering around an ion in the first solvation shell and, hence, of developing information on the solvation structure along the wavenumber axis rather than along the intensity axis of the spectra. It is shown that, taking the solution of Li⁺ClO₄^– in the 1:1 mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) as an example case, the Li⁺ ion is preferentially solvated by PC molecules [primarily as (PC)₃(DEC)₁Li⁺] and is totally protected from direct interaction (contact ion pairing) with the ClO₄^– ion. The solvation structures in neat PC and neat DEC solvents are also discussed.

A combination of heterodyne-detected sum frequency generation spectroscopy and theoretical modeling elucidates that the surface of ice I _h at 100 K has hydrogen order with the OH group pointing upward to the air (“H-up” orientation).