Viscosities of mixtures of SnR4 compounds and of some other large globular molecules. Effect of size difference

Solution viscosities have been measured at 25 °C on seven I systems of SnR4 compounds: SnBut4 with SnMe4, SnEt4, SnPr4, SnOct4, SnLaur4 and SnLaur4 with SnEt4 and SnPr4. The effect of shape difference on excess solution viscosities was investigated. The experimental value Δ ln ηexp = ln ηs − x1 ln η1 − x2 ln η2 was compared to Δ ln ηth.Δ ln ηth was obtained using ΔGM(mixing) in place of GM≠(activation) and free volume theories. Experimental heats of mixing have been measured and are used inΔ ln ηth. It was found that with the Van der Waals model for the energy, the difference Δ ln ηexp − Δ ln ηth, indicative of the agreement between the predicted and experimental value, is relatively small for mixtures of molecules not having a large size difference. However, for systems different in size, Δ ln ηexp − Δ ln ηth is positive and large and is shown to be an increasing function of the size difference. Δ ln ηth could be adjusted to Δ ln ηexp by adding a term ln ηΔV* = c(V1*1/2 − V2*1/2)2 where V* is the core volume. To confirm the validity of ln ηΔV*, the seven II systems chosen in order to present a large range (V1*1/2 − V2*1/2) were measured: SnBut4 + squalane, Si(OEt)4 + Si(OOct)4, n-C10 + Si(OOct)4, Si(OEt)4 + squalane, n-C12 + SnOct4, Si(OMe)4 + Si(OOct)4, n-C16 + benzene. A c value of 5.3 × 10−3 cm3 appears to be adequate for all the systems studied in this work. The 'condensation effect' of SnEt4 and SnPr4 observed by calorimetry is possibly seen here in the series SnLaur4 with SnEt4, SnPr4, SnBut4.