Handbook of Solvents - George Wypych - ChemTech - Ventech!

12
Other Properties of Solvents,
Solutions, and Products
Obtained from Solutions
12.1 RHEOLOGICAL PROPERTIES, AGGREGATION, PERMEABILITY,
MOLECULAR STRUCTURE, CRYSTALLINITY, AND OTHER
PROPERTIES AFFECTED BY SOLVENTS
George Wypych
ChemTec Laboratories, Inc., Toronto, Canada
12.1.1 RHEOLOGICAL PROPERTIES
The modification of rheological properties is one of the main reasons for adding solvents to
various formulations. Rheology is also a separate complex subject which requires an
in-depth understanding that can only be accomplished by consulting specialized sources
such as monographic books on rheology fundamentals. 1-3 Rheology is such a vast subject
that the following discussion will only outline some of the important effects of solvents.
When considering the viscosity of solvent mixtures, solvents can be divided into two
groups: interacting and non-interacting solvents. The viscosity of a mixture of
non-interacting solvents can be predicted with good approximation by a simple additive
rule rule:
i= n
= ∑ i i
i=
1
logη φ logη
[12.1.1]
where:
η viscosity of solvent mixture
i iteration subscript for mixture components (i = 1, 2, 3, ..., n)
φ fraction of component i
ηi viscosity of component i.
Interacting solvents contain either strong polar solvents or solvents which have the
ability to form hydrogen bonds or influence each other on the basis of acid-base interaction.
Solvent mixtures are complicated because of the changes in interaction that occurs with
changes in the concentration of the components. Some general relationships describe vis-