Surfactant double layer stabilized magnetic nanofluids for biomedical application

Abstract

Magnetite nanoparticles were coated with surfactant double layers in order to prepare waterbased magnetic fluids (MFs). The effects of head group (sulfonate, carboxylate) and alkylchain length (11–17 C atoms) and the combination of surfactants were studied. Adsorption,dynamic light scattering (DLS) and electrophoretic mobility measurements were performed.The quantity of surfactant varied between 0.3 and 0.5 g, i.e. their specific amount ranges over1.5–2 mmol g−1 magnetite in MFs. The adsorption isotherm of Na oleate on magnetite proved the double layer formationwith 2 mmol g−1 saturation value in good harmony with the empirical doses. The effect of diluting MFs, pHand salt concentration was studied. The pH-dependent stability and the salt tolerance ofMFs were different owing to the dissociation of the outermost hydrophilic groups and thehydrophobic interactions scaling with the alkyl chain length of surfactant. Thehydrophobic interactions are favored only for oleic and myristic acid double layers. Inthese MFs, aggregation cannot be observed even in fairly dilute systems up to thephysiological salt concentration around neutral pH 6–8 favored in biomedicalapplication. The stable oleic and myristic acid double layers can hinder effectively theaggregation of magnetite particles due to the combined steric and electrostaticstabilization.