COOPERATIVE ADSORPTION OF NONIONIC AND ANIONIC SURFACTANTS TO THE SURFACE OF HYDROXYAPATITE IN AN AQUEOUS PHASE

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Adsorption of polyethyleneglycol mono-p-isooctylphenylether (TX-100) on hydroxyapatite (HAP) was accelerated in the presence of sodium dodecylsulfate (SDS). This is because TX-100 was captured into hemimicelle/ admicelle of SDS formed on the surface of HAP. The adsorption amount on and affinity to HAP of TX-100 increased with the adsorption amount of SDS, forming the mixed micelle on the surface. Sodium dodecylbenzenesulfonate (SDBS) was also adsorbed on HAP in the same manner as that of SDS. However, polyoxyethylene (23) laurylether (C12n23) was little adsorbed by itself and scarcely accelerated the adsorption of SDBS. Anionic surfactants such as SDS and SDBS were adsorbed directly on the surface, while nonionic surfactants such as TX-100 and C12n23 required hydrophobic area to be adsorbed on the surface. The hydrophobic patch on the surface should be formed after the adsorption of the anionic surfactant on HAP. The roles of hydrophobic interaction and cooperative adsorption in the adsorption of nonionic surfactants were discussed.