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Surface analysis of magnetite nanoparticles in cyclohexane solutions of oleic acid and oleylamine

“…An estimate of À5k B T (À12 kJ/mol) can be given for the adsorption free energy F ads , using K ¼ e ÀF ads =k B T ¼ 115 from a fit of the adsorption isotherm. This adsorption free energy is of the same order as the adsorption energies calculated by Korolev et al [7] from temperature-dependent adsorption data for oleic acid on magnetite in hexane. For the strong adsorption sites, the adsorption free energy is significantly larger than À5k B T.…”

“…They found a plateau value of about 3.5 AE 0.4 adsorbed molecules per nm 2 at 10 mM oleic acid. Korolev et al [7] used in situ IR analysis to study the adsorption of oleic acid on magnetite particles (prepared in water) in hexane solutions; they do not give absolute coverages, but the surface coverage attains a plateau in about the same concentration range as in our measurements. Surfactant adsorption apparently strongly depends on how the nanoparticles are prepared, since a plateau is reached at significantly lower concentration by Dubois et al [6], and complete desorption is observed at low surfactant concentrations by Korolev et al [7], in contrast to our findings and those of Dubois et al [6].…”

“…Korolev et al [7] used in situ IR analysis to study the adsorption of oleic acid on magnetite particles (prepared in water) in hexane solutions; they do not give absolute coverages, but the surface coverage attains a plateau in about the same concentration range as in our measurements. Surfactant adsorption apparently strongly depends on how the nanoparticles are prepared, since a plateau is reached at significantly lower concentration by Dubois et al [6], and complete desorption is observed at low surfactant concentrations by Korolev et al [7], in contrast to our findings and those of Dubois et al [6]. The presence of a fractional monolayer is supported by other techniques: both from statistical analysis of the particle-particle contact distance observed by TEM [11] and from small angle neutron scattering (SANS) [30], a surfactant layer of about 2 nm thickness was deduced.…”

“…3), a strong new band appears at 626 cm À1 that can be attributed to vibrations of the crystalline lattice of nanocrystalline magnetite [7,24,25]. At low surfactant concentration (Fig.…”

“…Oleylamine affects the synthesis of nanoparticles of various materials, including FePt [2], FeMo [3], and magnetite (Fe 3 O 4 ) [3,5], although the mechanism remains unclear. Moreover, surfactant desorption is expected to take place during the chemical purification steps at the end of the synthesis, but few studies mention quantitative information about this problem [6,7]. Surfactant adsorption on nanoparticles is an important issue, since it not only affects the colloidal stability but also the optical [8] and magnetic properties [9][10][11].…”