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The Effect of Addition of Ionic Surfactants on the Flocculation-Deflocculation Behabior of Sulfathiazole and Other Suspensions

1974; Pharmaceutical Society of Japan; Volume: 94; Issue: 7 Linguagem: Inglês

10.1248/yakushi1947.94.7_833

1347-5231

Yasuhiko Nakamura, Akinobu OTSUKA, Masayuki Nakagaki,

Minerals Flotation and Separation Techniques

The flocculation-deflocculation behavior of sulfathiazole, α-alumina, and graphite in the solutions of dodecylamine hydrochloride (DAHCl) and of sodium dodecyl sulfate (SDS) was studied by means of sedimentation measurements, All of these powders showed flocculation in a very low concentration of each surfactant, suggesting that surfactant molecules were adsorbed nearly vertically with their ionic groups attached to the solid surfaces and, hence, the surfaces were rendered hydrophobic. With an increase in surfactant concentration, the deflocculating effect appeared to occur. It is likely therefore that in the second layer, the ionic groups were directed toward the solution. This view was supported by wettability measurements. Adsorption and electrokinetic measurements were also carried out in order to check the above concept and to investigate the mechanism of the interaction between solid surfaces and surfactant ions, in detail. The ζ-potential of all the samples in pure water was negative, while that of graphite was very small, and the addition of DAHCl changed the sign of ζ-potential. Sulfathiazole and alumina adsorbed SDS as well as DAHCl in spite of the same sign, although the amount of adsorption was found to be less than that of DAHCl. It would seem then that a small number of positive sites was also present on the surface of these solids. Graphite showed a high adsorption activity and the saturation amount for each surfactant exceeded to a large extent the monolayer capacity calculated from the surface area of the powder and the limiting area per a surfactant molecule at the air-water interface.