M. Colic et Dw. Fuerstenau, THE INFLUENCE OF SURFACTANT IMPURITIES ON COLLOID STABILITY AND DISPERSION OF POWDERS IN AQUEOUS SUSPENSIONS, Powder technology, 97(2), 1998, pp. 129-138
Surfactants have been used for different industrial and cosmetic purpo
ses for decades. Most industrial formulations are complex mixtures of
many different chemicals. Often, more than one component is surface ac
tive. In this paper we present the results of studies on the colloid s
tability and dispersion of metal oxide powders in anionic surfactant s
olutions with nonionic or long chain anionic surface-active impurities
. Dodecanol dramatically influenced anionic surfactant adsorption and
powder dispersion in mixed surfactant solutions. The enhancement of an
ionic surfactant adsorption modified the colloid stability of disperse
d metal oxides. At the same concentrations where powders were floccula
ted in the presence of pure anionic surfactants, stable dispersions we
re observed after addition of less than 1 wt.% of dodecanol, Similar e
ffects were observed in the presence of 1 wt.% of long chain anionic s
urfactant impurities. The modified flocculation/dispersion behavior is
caused by the enhanced coadsorption of nonionic and anionic surfactan
ts at the oxide-water interface, Even more interesting behavior was ob
served at pH values above the isoelectric point of oxides where partic
les and surfactants bare negative charge. Pure anionic surfactants can
not stabilize oxides at such pH values, but mixtures containing less t
han 1 mol% of dodecanol significantly stabilized hematite and anatase
at pH values above the isoelectric point. (C) 1998 Elsevier Science S.
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