چکیده (انگلیسی):

The aim of this work was to investigate the influence of some
non-ionic surfactants, Tween 80 and Brij 98, on the viscosity
and flow behavior of a commercial montmorillonite clay,
Veegum Granules. The effect of different concentrations of
the surfactants on the shear stress–shear rate rheograms of
hydrated concentrated clay suspensions was determined by
shear viscometry. The addition of either surfactant increased
the plastic viscosity and the yield stress of the suspensions.
Furthermore, both surfactants altered the thixotropy of the
suspensions to an extent that depended on both the surfactant
concentration and the time of equilibration of the surfactant
and Veegum. Brij 98 had a greater and more rapid effect. It is
proposed that the surfactant polar head-groups anchor at the
tetrahedral sheet surface, leaving the alkyl chains extending
away fromthe edges and faces. Consequently, the alkyl chains
undergo hydrophobic interactions that facilitate the association
between the platelets and increase the physical structure
within the suspension. Stereochemical differences between
the polar groups may lead to differences in the way the surfactants
associate with the tetrahedral sheet and hence their
ultimate effect on the rheological behavior. There is a significant
interaction between these surfactants and montmorillonite
clays, and the rheological changes that occur could have a
major impact on any pharmaceutical formulation that uses
these ingredients.