Transport properties excess contribution

If the terms of equation (7.13) are truly independent, then it may be appropriate to fit the dilute-gas transport properties to primary data at low density the dilute-gas contribution calculated from the resultant correlation can then be subtracted from the experimental data at higher densities to study the remaining excess and critical enhancement terms. Since the dilute-gas term is a function of temperature alone (or a reduced temperature such as T = T/Tc or T = k T/i) and both the excess and critical enhancement terms are zero in the limit of zero density, the dilute-gas term is expected to be mathematically independent of the excess and critical enhancement terms. However, if the dilute-gas term has some cross correlation with respect to density (because of its determination from experimental data at nonzero density), then it may not be proper to fit the dilute gas data independently. Any cross correlation which is present in the data is not necessarily due to the behavior of the transport property itself, but may be due to systematic effects. This uncertainty may be a function of the other independent variables such as density or composition. 

The form of equation (14.46) indicates that it is relatively straightforward to calculate the excess transport property fi om the experimental data by subtracting the dilute-gas contribution and the critical enhancement. As mentioned before, in practice an iterative procedure is often necessary. Here, for the purpose of discussion it will be assumed that... 

The components of ionic liquids (ions) are constrained by high coulombic forces and thus exert practically no vapor pressure above the liquid surface. Importantly, the near-zero vapor pressure (nonvolatile) property of ionic liquids means they do not emit the potentially hazardous volatile organic compounds (VOCs) associated with many industrial solvents during their transportation, handling, and use. (It should be noted, however, that the decomposition products of ionic liquids from excessive temperatures can have measurable vapor pressures.) In addition, they are nonexplosive and nonoxidizing (nonflammable). These characterizations could contribute to the development of new reactions and processes that provide significant environmental, safety, and health benefits compared to existing chemical systems. 

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