The prediction of high-pressure volumetric properties of compressed liquids using the two states model

In this work, we argue that the volumetric properties of liquids cannot be reproduced by a single isothermal equation of state derived by the compressibility route for the whole pressure region extended up to a GPa pressure but require the consideration of two states associated with qualitatively different molecular packing properties. This is confirmed by examples of polar and non-polar substances within the range of temperatures from 203.15 K to 491.48 K and pressures up to 1200 MPa. The proposed two states model is truly predictive for the high-pressure density and isothermal compressibility using several easily measurable physico-chemical quantities: the density, the isobaric heat capacity, and the speed of sound at atmospheric pressure only. The experimental data on the density for 15 different compressed liquids, given in the literature as a function of temperature and very high-pressures, were used for the comparison and its analysis. The relative absolute average deviation for 2138 experimental data points by a two states model is close to 0.17%.

Experimental Evidence for a State-Point-Dependent Density-Scaling Exponent of Liquid Dynamics

A large class of liquids obey density scaling characterized by an exponent, which quantifies the relative roles of temperature and density for the dynamics. We present experimental evidence that the density-scaling exponent γ is state-point dependent for the glass formers tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl ether (5PPE). A method is proposed that from dynamic and thermodynamic properties at equilibrium estimates the value of γ. The method applies at any state point of the pressure-temperature plane, both in the supercooled and the normal liquid regimes. We find that γ is generally state-point dependent, which is confirmed by reanalyzing data for 20 metallic liquids and two model liquids.

International Standard for viscosity at temperatures up to 473 K and pressures below 200 MPa (IUPAC Technical Report)

This paper presents the results of an investigation into possible liquid viscosity standards to meet an industrial requirement for a liquid with a nominal viscosity of 20 mPa s at a temperature of 473 K and pressure of 200 MPa with a relative expanded uncertainty of less than 5%. There are no commercially available certified viscosity reference liquids that meet this requirement. Four candidate fluids were examined: squalane, Krytox GPL102, tris(2-ethylhexyl) trimellitate (TOTM), and dipentaerythritol hexa(3,5,5-trimethylhexanoate) (DiPEiC9). Although none of these fluids satisfies all of the criteria, two fluids were identified as being suitable as International Standards for viscosity at temperatures up to 473 K and pressures below 200 MPa. These fluids are squalane and tris(2-ethylhexyl) trimellitate (TOTM), which at T=473.15 K and p=200 MPa present viscosity values of 5 mPa s and 10 mPa s, respectively.