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Magnetic Particle Self-Assembly at Functionalized Interfaces



Apurve Saini, Katharina Theis-Brohl, Alexandros Koutsioubas, Kathryn L. Krycka, Julie Borchers, Max Wolff


We study the assembly of magnetite nanoparticles in water-based ferrofluids in wetting layers close to silicon substrates with different functionalization without and with an out-of-plane magnetic field. For particles of nominal sizes 5 nm, 15 nm and 25 nm, we extract density profiles form neutron reflectivity measurement. We show that self-assembly is only promoted by a magnetic field if a seed layer is formed at the silicon substrate. Such a layer can be formed by chemisorption of activated N-hydroxysuccinimide ester-coated nanoparticles at an (3-aminopropyl)triethoxy silane functionalized surface. Less dense packing is reported for physisorbtion of the same particles at a piranha treated (strongly hydrophilic) silicon wafer and no wetting layer is found for a self-assembled monolayer of octadecyltrichlorosilane (strongly hydrophobic) at the interface. We show that once the seed layer is formed and under an out-of-plane magnetic field further wetting layers assemble. These layers become denser with time, larger magnetic fields, higher particle concentrations and larger moment of the nanoparticles.


Magnetic nanoparticles, Self-assembly, Dipole interactions, Polarized neutron reflectivity, SANS


Saini, A. , Theis-Brohl, K. , Koutsioubas, A. , Krycka, K. , Borchers, J. and Wolff, M. (2021), Magnetic Particle Self-Assembly at Functionalized Interfaces, Langmuir (Accessed June 23, 2024)


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Created April 12, 2021, Updated September 29, 2021