Inside out Approach to Rotator State in Hydrogen-Bonded System—Experimental and Theoretical Cross-Examination in n-Octanol

Abstract

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from −84 ∘C to −15 ∘C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from −30 ∘C to −15 ∘C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car–Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect’s influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated—the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Supercriticality, Glassy Dynamics, and the New Insight into Melting/Freezing Discontinuous Transition in Linseed Oil

“…therein. They can be as follows [62,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]: (i) premelting effects are 'weak' and rangelimited, (ii) they are detected only for some systems, (iii) they are detected for selected physical properties, (iv) there are no reports on their parameterization, except the very recent ref. [72], and (v) no solid-state pretransitional effects for freezing, i.e.…”

“…Despite the apparent limitations and problems, premelting effects are commonly considered the gateway for explaining the nature of melting/freezing discontinuous phase transitions [62,72,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]. This cognitive situation is qualitatively different from continuous phase transitions: understanding their origins is one of the greatest universalistic successes of 20th-century physics, as concluded in Critical Phenomena Physics [33].…”

“…For melting/freezing discontinuous transitions, such pretransitional effects are (almost) absent, except for the puzzling premelting effects in the solid state [62,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]. In linseed oil, both premelting and post-freezing effects exist, and the latter are even stronger and longer ranged.…”

Dielectric Relaxation in Nanocrystals: A Scale Effect

“…The scale effect in the melting process of nanocrystals has attracted the attention of many researchers; − several models have been proposed to explain how the size of the crystal affects both the melting temperature and the enthalpy of fusion. − However, the research is somewhat lacking as to the impact of spatial restrictions in nanocrystals on dielectric relaxation, − even though the relaxation processes can provide useful insight into the mechanisms of thermal motion of molecules in the nanosized inclusions in porous matrices. In this motion, the matrix can both hinder ,− and activate certain mobility of embedded molecules . This is not an idle theoretical question, as it has immediate practical applications: this is what allows one to program the release rate of drugs or to determine the thermal interval of a drug’s pharmacological activity. , …”