Raman scattering and water structure in nonionic amphiphile solutions

The structure of water in aqueous solutions of polyoxyethylene nonionic amphiphiles C₁₀{E}₅$, where ${E}₅$ denotes ${H}₂₁$(${OCH}₂CH₂{)}₅$OH, is studied by Raman scattering along an isothermal path crossing the isotropic one-phase region from 0 to 1 amphiphile volume fraction {φ}. The isotropic OH stretching-vibration spectrum points out a water behavior that depends on the amphiphile concentration. The data analysis is performed using the bond-percolation model developed for water. The interpretation of scattering data leads to the following structural picture for the water in the systems: for {φ} lower than 0.75, water is partially bound to the oxyethylene groups of the amphiphile; above {φ}=0.75 all water present in the system is bound. Analogously to the behavior of water in confined geometries, the structure of bound water presents a local fourfold-coordinated environment.