Handbook of Solvents - George Wypych - ChemTech - Ventech!

520 Y. Y. Fialkov, V. L. Chumak
Figure 9.3. Classification of viscosity isotherms for binary solvents.
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Type II - S-shaped viscosity curves (∂η / ∂x≠ 0, ∂ η / ∂x²=0attheinflection
point).
This type of isotherm is attributed to systems which have components differing substantially
in viscosity, but have low yield of heteromolecular associates to form local maximum
in isotherms. Systems such as sulfuric acid-pyrosulfuric acid and diphenylamine - pyridine
are examples of this kind of viscosity isotherm.
Type III combines viscosity isotherms, which are convex-shaped from composition
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axis as its common attribute, i.e., ∂η/ ∂x²
< 0. In the whole concentration range, we have
E
positive values of excessive viscosity η = ηexp −[( η1−η2 ) x+ η2,
where ηexp is experimental
value of viscosity. It shall be mentioned that, although the term η E is used in literature,
unlike the excessive logarithm of viscosity (lnη) E =lnηexp - (lnη1/η2 +lnη2), it has no physical
meaning.Viscosity isotherms of this type for interacting liquid systems are most commonly
encountered and have shape diversity, which can be divided into three subtypes.
Subtype IIIa - isotherms monotonically convex shaped from composition axis, but
without maximum (in the whole composition range ∂η / ∂x≠
0).
Dependence viscositycomposition
of water-monochloroacetic acid can serve as an example.
Subtype IIIb - isotherms with “irrational” maximum (i.e., with maximum which does
not correspond to any rational stoichiometric correlation of components in mixed solvent).
This subtype is the most common case of binary mixed solvents with interacting compo-