Sorption van Tensiden an Festkörperoberflächen und ihre Bedeutung im Bereich der Arzneiformen

Abstract

The adsorption of surfactants at the solid liquid interface and their consequences in drug preparation. In dispersions of organic solvents the adsorption of surfactants at solid interfaces (i.e. SiO2) is influenced by the interactions with the functional groups at the surface, the adsorption of the solvent and by solvation. Strong polar solvents (alcohols, DMSO) reduce the adsorption of surfactants, which is due hydrogen bonds, by displacement from adsorption sites, while in solvents like CHCl3 strong solvation reduce the interactions with the solid surface. At the solid water interface the adsorption of non-ionic surfactants (PEG-nonylphenols) is decreased by water structure breaking anions while structure making anions increase it. The adsorption of ionogenic surfactants onto solid surfaces from aqueous solutions is increased by neutral salts, if there is no competitive adsorption concerning the salt ions. At equivalent salt concentrations the amount of adsorption depends on the water structure effects of the surfactant counter ions. Structure breaking ions increase adsorption values more than structure making ions. The co-ions show no different effect in this respect. Strongly adsorbed inorganic polyvalent ions like sulphate or phosphate can change the adsorption behaviour of solid substances: They react as secondary adsorption sides for oppositely charged surfactant ions. Rheological properties of suspensions, lotions, ointments are as well influenced as drug availability from solid and semi-solid dosage forms by the adsorption of surfactants.