Investigation of orientational correlations and structural transitions in neat liquids

Abstract

The temperature dependence of depolarized light scattering intensity (DLSI) and nuclear magnetic resonance (NMR) chemical shift were measured for hexafluorobenzene in the temperature range from 10 to 63 °C. The DLSI curve is not monotone, consists of regions of different slope, and has a dip near 47 °C. The chemical shift curves also consists of different slope straight regions whose separation temperatures are coincident with anomalies on the DLSI curve. As DLSI is directly dependent on effective anisotropy of molecules, the authors suggest that in liquid C6F6, the regions of different slope correspond to molecular structures with different local order and symmetry. The authors derive the conclusion that in liquid C6F6 there are transitions between local structures generated by dimers with small differences between their minimum potential energy.

Neutron Diffraction and Molecular Dynamics Study of Liquid Benzene and Its Fluorinated Derivatives as a Function of Temperature

“…As noted previously structural investigations on liquid benzene combining neutron diffraction and molecular dynamics simulations to study the evolution of the local ordering along the liquid−vapor coexistence curve (from temperatures close to the melting point up to the boiling point) have not been reported so far. Similarly, for hexafluorobenzene only measurements combining X-rays and neutron diffraction have been reported at room temperature. , The only available and indirect structural information concerning the temperature dependence of the local ordering for these two liquids has been obtained from the integrated intensity of depolarized light scattering. , It was found that a transition between local structures generated by dimers could be detected in both neat liquids. In contrast high-resolution stimulated Brillouin gain spectroscopy measurements show no evidence of “structural transition” …”

Unconventional density dependence of the stochastic dynamics in an organic liquid

“…It has been interpreted [24,25] as a dynamical transition within the liquid state. In fact, for most systems the findings at microscopic scales can be correlated with well-defined features in macroscopic thermodynamic quantities such as the specific heat [24,26] or even some transport properties such macroscopic shear viscosity and surface tension [27] which may show a noticeable curvature within a restricted range of temperatures.…”

Microphase separation as the cause of structural complexity in 2D liquids

“…To this end, we would like to draw attention to the behavior observed in liquid Benzene (ref. 32) and Quinolene (ref. 33) where scattering experiments using traditional equilibration times (hours) found at temperatures close to crystallization an increased data scatter, but some peaks in the temperature dependencies of small-scale characteristics when the equilibration times were an order of magnitude longer.…”

“…The small size of the ordered nuclei and the expected relatively small differences in internal energies between these nuclei and the surrounding less-ordered material can create challenging condition for experimental observation of the equilibrium mosaic state, especially a necessity to use unusually long equilibration times for the mosaic to form. To this end, we would like to draw attention to the behavior observed in liquid Benzene [33] and Quinolene [34] where scattering experiments using traditional equilibration times (hours) found at temperatures close to crystallization an increased data scatter, but some peaks in the temperature dependencies of small-scale characteristics when the equilibration times were an order of magnitude longer.…”