Interplay between structural static and dynamical parameters as a key factor to understand peculiar behaviour of associated liquids

Abstract

In this article, we have addressed fundamental relationships between the chemical structure, intermolecular order, degree of the association and the dynamical properties, including the nature of dielectric response function, the variation of the glass transition temperature and the Kirkwood factor in three homologues phenyl derivatives of monohydroxy alcohols: 1-phenyl-2-butanol, 4-phenyl-1-butanol, and 4-phenyl-2-butanol. Dielectric data supported by infrared and diffraction investigations allowed us to certify that the Debye relaxation can be detected not only in aliphatic but also aromatic monohydroxy alcohols, suggesting its universal character, irrespectively of the chemical structure and steric hindrance. Moreover, we discovered that besides water, 4-phenyl-1-butanol is a next H-bonded system that exhibits the Debye-like relaxation process and no sign of the diffraction pre-peak being a fingerprint of the medium-range intermolecular order. This finding alters our understanding of the molecular origin of the scattering pre-peak and Debye-type process in diffractograms and dielectric loss spectra, respectively. Finally, we revealed that the activation volume, which is a measure of the volume required for reorientational motions of molecules to occur, is the greatest for the system with the highest Kirkwood factor at the glass transition temperature. It means that except the static parameters characterising the size of the supramolecular associates, their morphology, and the degree of intermolecular order, also dynamical quantity related to the volume of relaxing supramolecular structures is required to understand the fluctuations in the Kirkwood factor, and generally, the behaviour of associating liquids at varying thermodynamic conditions.