Testing the Lorentz–Lorenz relation in the near-critical binary fluid mixture isobutyric acid and water

Abstract

The refractive index in each phase of the binary fluid mixture isobutyric acid and water was measured at temperatures below the system’s upper consolute point. This data was combined with existing density data to test the Lorentz–Lorenz relation in a near-critical binary fluid mixture. The Lorentz–Lorenz relation is verified within experimental error (0.5%) when the volume change on mixing the components is taken into account. The density coexistence curve data is reanalyzed to determine the critical exponent β and amplitude B. By allowing the order parameter to be a definition of the volume fraction that includes volume loss on mixing, a very symmetric coexistence curve is obtained which can be described by simple scaling with β=0.326±0.003 and B=1.565±0.021. This exponent agrees with theoretical predictions while the amplitude, when combined with existing turbidity data, confirms two-scale-factor universality. The amplitude obtained by analyzing the coexistence curve when the refractive index is the order parameter also combines with turbidity data to confirm two-scale-factor universality, but does not require knowledge of the volume loss on mixing or the composition dependence of the refractive index.

Transcritical oxygen/transcritical or supercritical methane combustion

“…The difficulty, in the present situation, is to account for the near critical behavior of the refractive index. Experimental observations indicate that the Lorenz-Lorentz law R = (1/q) {(n 2 À 1)/(n 2 + 2)} can be used to predict the change of refractive index n knowing the change in density [9]. Accordingly, the refractivity constant depends on the chemical nature of the medium, and q is the density at the pressure and temperature at which n is measured [10].…”

Asymmetric criticality in weakly compressible liquid mixtures

“…44 The validity of this assumption is not obvious, 45,46 but some experiments seem to indicate that deviations may be negligible in practice. 47,48 Another approach ͑IIb͒ is to convert n͑T͒ data into x͑T͒ by using the previously experimentally determined n͑T , x͒ function that describes the behavior of n as the one-phase region close to the phase boundary, as adopted by An et al 49 The accuracy of this procedure depends on the accuracy of the calibration function n͑T , x͒. Method II has the advantage that it directly provides data for the coexisting phase as a function of temperature for a single sample.…”

Liquid-liquid criticality in the dielectric constant and refractive index: A perspective

“…The critical behaviour of n(T ) was a subject of long controversy from an experimental viewpoint and is often neglected due to its (typically) very small size [65][66][67][68]. Early attempts to detect an anomaly in n(T ) were unsuccessful, its size being of the order of the sensitivity of the instrument [69]. For UCST-type of mixtures like nitromethane-isooctane [70,71] and isobutyric acid-water [71], the anomaly in n was concluded to be a consequence of the anomaly in the mass density ρ, while for nitroethane-cyclohexane [72], a possible intrinsic contribution fell within the experimental uncertainty limits.…”