Ternary systems critical phenomena

The alkane mixtures provide the prototypical examples of type I type V behavior. Methane + hexane (and higher alkanes), ethane + octadecane, and propane + pentatriacontane are all type V. The upper LL regions of these systems are noteworthy in that the temperature difference between the UCEP and the LCEP seems to monotonically increase with increasing carbon number. Ultimately, this trend must reverse as type III behavior sets in, but no indication of this reversal has been observed experimentally. Mixtures of methane with hexane isomers provide unusual examples of type V phase behavior. Type V behavior is exhibited for all isomers except 2,2-dimethyl butane. Ternary mixtures of methane with the 2,2 and 2,3-isomers provide a rare example of tri-critical behavior. Turning to another example, the type V LLV locus becomes extremely short as the asymmetry of the mixture increases to the point where transition to type III behavior is approached. Ethane + p-dichlorobenzene provides an example of this phenomenon, with an LLV locus extending over a mere 0.6K.[ Such an odd effect may seem to have little practical significance, unless one considers the impact of an unexpected precipitation on a critical pipeline. 

The intensity of light scattered from a fluid system increases enormously, and the fluid takes on a cloudy or opalescent appearance as the gas-liquid critical point is approached. In binary solutions the same phenomenon is observed as the critical consolute point is approached. This phenomenon is called critical opalescence.31 It is due to the long-range spatial correlations that exist between molecules in the vicinity of critical points. In this section we explore the underlying physical mechanism for this phenomenon in one-component fluids. The extension to binary or ternary solutions is not presented but some references are given. 

---