Efficient Control of the Rheological and Surface Properties
of Surfactant Solutions Containing C8–C18 Fatty Acids as Cosurfactants
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Abstract
Systematic experimental
study is performed about the effects of
chain length (varied between C8 and C18) and concentration of fatty
acids (FAc), used as cosurfactants to the mixture of the anionic surfactant
SLES and the zwitterionic surfactant CAPB. The following properties
are studied: bulk viscosity of the concentrated solutions (10 wt %
surfactants), dynamic and equilibrium surface tensions, surface modulus,
and foam rheological properties for the diluted foaming solutions
(0.5 wt % surfactants). The obtained results show that C8–C10
FAc induce formation of wormlike micelles in the concentrated surfactant
solutions, which leads to transformation of these solutions into viscoelastic
fluids with very high apparent viscosity. The same FAc shorten the
characteristic adsorption time of the diluted solutions by more than
10 times. In contrast, C14–C18 FAc have small effect on the
viscosity of the concentrated solutions but increase the surface modulus
above 350 mN/m, which leads to higher friction inside sheared foams
and to much smaller bubbles in the formed foams. The intermediate
chain C12 FAc combines some of the properties seen with C10 FAc and
other properties seen with C14 FAc. These results clearly demonstrate
how appropriate cosurfactants can be used for efficient control of
the rheological properties of concentrated surfactant solutions and
of some important foam attributes, such as bubble size and foam rheology