Lorentz-Lorenz Coefficient, Critical Point Constants, and Coexistence Curve of 1,1-Difluoroethylene

TL;DR

This study measures the Lorentz-Lorenz coefficient, critical temperature, and density of 1,1-difluoroethylene, revealing a stronger density dependence than other fluids and providing precise critical point data.

Contribution

It provides the first detailed measurement of the Lorentz-Lorenz coefficient's density dependence for 1,1-difluoroethylene, improving the accuracy of optical-density transformations in fluid critical phenomena studies.

Findings

Lorentz-Lorenz coefficient decreases monotonically with density.

No anomaly observed near the critical density.

Critical temperature and density precisely measured.

Abstract

We report measurements of the Lorentz-Lorenz coefficient density dependence, the critical temperature, and the critical density, of the fluid 1,1-difluoroethylene. Lorentz-Lorenz coefficient data were obtained by measuring refractive index and density of the same fluid sample independently of one another. Accurate determination of the Lorentz-Lorenz coefficient is necessary for transformation of refractive index data into density data from optics-based experiments on critical phenomena of fluid systems done with different apparatus, with which independent measurement of the refractive indes and density is not possible. Measurements were made along the coexistence curve of the fluid and span the density range 0.01 to 0.80 g/cc. The Lorentz-Lorenz coefficient results show a stronger density dependence along the coexistence curve than previously observed in other fluids, with a monotonic decrease from a density of about 0.2 g/cc onwards, and an overall variation of about 2.5% in the density range studied. No anomaly in the Lorentz-Lorenz coefficient was observed near the critical density. The critical temperature is measured at Tc=(302.964+-0.002) K (29.814 C) and the measured critical density is (0.4195+-0.0018)g/cc.