Hamaker Constants of Iron Oxide Nanoparticles

Faure, Bertrand; Salazar-Alvarez, Germán; Bergström, Lennart

doi:10.1021/la201387d

Cited by 130 publications

(89 citation statements)

References 60 publications

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“…S6). This demonstrates that the nanoparticle shape is crucial for the regular self-assembly (17). In some cases irregularly shaped small clusters (n < 30) were obtained, as shown by the cryo-TEM images (SI Appendix, Fig.…”

Section: Significancementioning

confidence: 65%

Self-assembly of smallest magnetic particles

Taheri

Michaelis

Friedrich

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The assembly of tiny magnetic particles in external magnetic fields is important for many applications ranging from data storage to medical technologies. The development of ever smaller magnetic structures is restricted by a size limit, where the particles are just barely magnetic. For such particles we report the discovery of a kind of solution assembly hitherto unobserved, to our knowledge. The fact that the assembly occurs in solution is very relevant for applications, where magnetic nanoparticles are either solutionprocessed or are used in liquid biological environments. Induced by an external magnetic field, nanocubes spontaneously assemble into 1D chains, 2D monolayer sheets, and large 3D cuboids with almost perfect internal ordering. The self-assembly of the nanocubes can be elucidated considering the dipole-dipole interaction of small superparamagnetic particles. Complex 3D geometrical arrangements of the nanodipoles are obtained under the assumption that the orientation of magnetization is freely adjustable within the superlattice and tends to minimize the binding energy. On that basis the magnetic moment of the cuboids can be explained.M agnetic particles show an intriguing self-assembly behavior, due to mutual magnetic interactions or interaction with external magnetic fields. This can already be experienced by playing with toy magnets, which can assemble into strings or clusters. For much smaller magnetic particles, the knowledge about the magnetic assembly is crucial for technical applications involving magnetorheological fluids (1), high-density magnetic storage devices, hyperthermal cancer therapy, and magnetic resonance imaging (2). These applications use small magnetic particles, in the micrometer size range for magnetorheological fluids and down to 10 nm for magnetic resonance imaging or magnetothermal cancer therapy. Decreasing the size of the particles further decreases their magnetic moment to an extent that they are not considered in those applications anymore. In consequence, the assembly of sub-15-nm magnetic nanoparticles has been scarcely explored (3). Only recently, it was reported that cube-shaped magnetic nanoparticles of 13 nm showed a surprising magnetic-field-induced assembly into helices at the air-liquid interface (4) and 9-nm magnetic nanoparticles in the presence of a magnetic field uniquely assembled into very large, nearly defectfree monolayers and 3D cubic assemblies on solid substrates (5). This triggers the question about the arrangement of the magnetic dipoles in such assemblies where an amazing answer was recently found in the case of only eight dipoles (6), and where for larger magnetic nanoparticles and their assemblies considerable complexity was observed (7, 8).Here we report very small (sub-15-nm diameter) spherical and cube-shaped iron-oxide nanoparticles with respect to their magnetic assembly behavior. The nanoparticles are sterically stabilized by oleic acid, have very narrow size distributions, and very regular shapes (SI Appendix). The controlled synthesis of...

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Section: Significancementioning

confidence: 65%

Self-assembly of smallest magnetic particles

Taheri

Michaelis

Friedrich

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…[23] A recent discussion on the values of Hamaker constants of iron oxide NPs can be found in a paper by Faure. [24] It can be calculated as: …”

Section: Van Der Waals Forcesmentioning

confidence: 99%

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

2016

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The current state of the art in the use of colloidal methods to form nanoparticle assemblies, or clusters (NPCs) is reviewed. The focus is on the two-step approach, which exploits the advantages of bottom-up wet chemical NP synthesis procedures, with subsequent colloidal destabilization to trigger assembly in a controlled manner. Recent successes in the application of functional NPCs with enhanced emergent collective properties for a wide range of applications, including in biomedical detection, surface enhanced Raman scattering (SERS) enhancement, photocatalysis, and light harvesting, are highlighted. The role of the NP-NP interactions in the formation of monodisperse ordered clusters is described and the different assembly processes from a wide range of literature sources are classified according to the nature of the perturbation from the initial equilibrium state (dispersed NPs). Finally, the future for the field and the anticipated role of computational approaches in developing next-generation functional NPCs are briefly discussed.

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“…Based on published Hamaker constants, ATiO2-TiO2=15.3×10 -20 J (Bergström, 1997), AH2O-H2O= 3.7×10 -20 J (Israelachvili, 2011), and AFeOx-FeOx= 68×10 -20 J (Faure, 2011). Hamaker constant of nTiO2-water-Fe oxyhydroxides was determined to be ATiO2-H2O-FeOx= 1.257×10 -19 J using Equation (6).…”

Section: Ntio2 Attachment To Sand At Various Ha Concentrationsmentioning

confidence: 99%

Stability of nTiO 2 particles and their attachment to sand: Effects of humic acid at different pH

Cheng

2016

Science of The Total Environment

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Influence of humic acid (HA) on stability and attachment of nTiO2 particles to sand was investigated. Results showed that HA can either promote or hinder nTiO2 stability, depending on pH and HA concentration. HA can either enhance or reduce nTiO2 attachment to Fe oxyhydroxide coating at pH 5, depending on HA concentration.Results further showed that at pH 5, Fe oxyhydroxide coating reduced nTiO2 attachment to sand in the absence of HA but increased nTiO2 attachment in the presence of low concentration of HA. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was invoked to analyze particle-to-particle and particle-to-sand interactions in order to elucidate the roles of pH, HA, quartz, and Fe coating in controlling nTiO2 stability and attachment. Overall, this study showed that changes in zeta potential of nTiO2 and Fe coating due to pH changes and/or HA adsorption are the key factors that influence stability and attachment of nTiO2.iii ACKNOWLEDGEMENTS

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Hamaker Constants of Iron Oxide Nanoparticles

Cited by 130 publications

References 60 publications

Self-assembly of smallest magnetic particles

Self-assembly of smallest magnetic particles

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

Stability of nTiO 2 particles and their attachment to sand: Effects of humic acid at different pH

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