Molar excess thermodynamic quantities hE, [Formula: see text], and vE have been measured at 25 °C over the whole composition range for mixtures of four globular Sn(CnH2n+1)4 (SnR4) (n = 1–4) with t-decalin, and 2,2,4,4,6,8,8-heptamethylnonane (br-C16) as well as hE for the same SnR4 compounds with 2,2,4-trimethylpentane (br-C8). The excess viscosities are measured at −20, 25, and 40 °C for the t-decalin + SnR4 systems. By introducing gE in the solution activation energy, the free energy of mixing can be related to and calculated from the excess viscosities. The steric hindrance contribution, corresponding to an increase of order or diminution of mobility in solution, known to occur either with compounds having highly substituted atoms or with flat-shaped molecules, was investigated. The free volume contribution to the different thermodynamic properties is calculated from the Prigogine–Patterson–Flory theory. The difference between the experimental and calculated excess data is associated with the steric hindrance contribution. Values of hE, [Formula: see text], vE, and sE confirm the existence of a large steric hindrance contribution (hE < −200 J mol−1 and TsE < −400 J mol−1 for two systems). Another contribution, found to occur for the two smaller globular SnR4, may originate in the liberation of movement induced in solution by the second component.
On the Origin of Excess Thermodynamic Quantities in Liquid Mixtures
