Hydrophilization of magnetic nanoparticles with an amphiphilic polymer revisited: Roles of nanoparticle capping density and polymer structure

• Published in: Applied surface science Vol. 570; p. 151171
• Main Authors: Lavorato, Gabriel C., Azcárate, Julio C., Rivas Aiello, Maria Belen, Orozco Henao, Juan Manuel, Mendoza Zélis, Pedro, Ceolin, Marcelo, Winkler, Elin, Fonticelli, Mariano H., Vericat, Carolina
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.12.2021
• Subjects: Fe3O4 nanoparticles; Interparticle magnetic interactions; Oleate capping density; Poly(maleic anhydride alt-1-octadecene); Polymer-nanoparticle assemblies; Oleate capping density; Interparticle magnetic interactions; Poly(maleic anhydride alt-1-octadecene); Polymer-nanoparticle assemblies; Fe3O4 nanoparticles
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.151171

[Display omitted] •Oleate-capped magnetite nanoparticles are encapsulated in an amphiphilic polymer.•The oleate surface density determines the success of the self-assembly process.•NP-polymer assemblies are only formed for polymer concentrations above 10 u/nm2.•Nanoparticles are individually wrapped in bilayer-like polymeric structures.•The amount of polymer in the assemblies modulates the effective magnetic anisotropy. Amphiphilic comb polymers, like poly(maleic anhydride-alt-1-octadecene) (PMAO), are frequently used to transfer hydrophobic magnetic nanoparticles (NPs) into aqueous media. While it is accepted that the hydrophilization is based on the interdigitation of the hydrocarbon chains from the polymer and the NP capping, the factors that determine the success of such process are still not fully understood. In this paper, some key aspects of the formation of water-soluble NP-PMAO assemblies from oleate-capped iron oxide NPs, not considered in previous works, are discussed thoroughly. We have found that the process is notably hindered when the chemisorbed oleates coverage decreases from 2.9 to 1.5 molecules/nm2, revealing the importance of the capping packing density in the assembly mechanism. Combined results from small-angle x-ray scattering and electron microscopy show that, for polymer concentrations ranging from 10 to 200 monomer units/nm2, the NPs are individually covered by polymer chains, although forming rather planar NP-PMAO assemblies which contain several NPs. Both the minimum polymer concentration needed for a successful hydrophilization (0.7 gPMAO/L) and the geometry of the assemblies suggest that intermolecular structures typical of comb polymers act as templates in the assembly process. Finally, we show that the magnetic properties are modulated by the polymer loading.