Isotope effects on the hydrodynamic fluctuations of self-associating fluids. A comparison between the Brillouin scattering of 1-octanol and its hydrocarbon chain perdeuterated analogue

Abstract

In this study we extend a previously developed theoretical model for concentration fluctuations of one-component fluids containing both associated and unassociated species. The model has been developed in order to explain the non-Landau behavior observed in self-associating fluids in the hydrodynamic regime. The complex dynamics for the different species formation is treated in the approximation of a pseudo two-components fluid formed by unbound molecules coexisting with a unique associated specie, the mean aggregation number of which is dictated by thermodynamic requirements. The model can be applied to rationalize the behavior of chain-forming hydrogen-bonding systems. Here, we report Rayleigh–Brillouin scattering data of 1-octanol and its chain perdeuterated analogue over a wide range of temperatures and wave vectors. The model explains, albeit qualitatively, most of the observed deviations from the Landau behavior observed in the Rayleigh–Brillouin spectra at different values of the k-vector.