Controlling the phase-separated morphology of a two-dimensional integrated layer of magnetic nanoparticles by surface modifications using immiscible amphiphiles

作者：Ohmura Kyohei; Yunoki Takeru; Shidara Yusaku; Iizuka Manami; Fujimori Atsuhiro^*

来源：Colloids and Surfaces A: Physicochemical and Engineering Aspects , 2017, 529: 462-474.

DOI：10.1016/j.colsurfa.2017.06.014

• Magnetic nanoparticles
• Phase separation
• Surface modification
• Immiscibility
• Method of organized molecular films

Surface modification with immiscible surfactants was utilized to induce phase separation at the nanometer scale in a two-dimensional particle layer of magnetic nanoparticles. Cobalt ferrite (CoFe2O4) particles (diameter = 30 nm) and magnetite (Fe3O4) particles (diameters = 5 and 30 nm) were typically subjected to surface modification with a hydrogenated and fluorinated long-chain carboxylic acid. A mixed monolayer of hydrogenated and fluorinated organo-magnetic nanoparticles was spread at the air/water interface. This system was used to assess the phase separation because the collapsed surface pressures of both components were individually observed in the isotherms that were measured by systematically changing the composition ratio. A nano-sized phase separation morphology was observed on the surface of the mixed single-particle layers by atomic force microscopy. A "sea-island" structure was observed in which the expanded phase formed by the fluorinated organo-magnetic nanoparticles surrounded the condensed nano-domains of the hydrogenated organo-magnetic nanoparticles. The separate (particulate) nano-phase morphology showed a temperature dependence, and in this case, the fluorinated "sea" phase transformed into a network morphology. The nano-domain of the hydrogenated organo-modified magnetic nanoparticles was a crystalline phase in which the modified chain was packed with two-dimensional hexagonal or orthorhombic systems. The nanophase separation on the surface of the magnetic single-nanoparticle layers likely formed because of repulsive interactions between the immiscible surface modifiers.

• 出版日期2017-9-20