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Self Assembly of Magnetic Nanoparticles at Silicon Surfaces



Katharina Theis-Brohl, Philipp Gutfreund, Alexei Vorobiev, Max Wolff, Boris P. Toperverg, Joseph Dura, Julie Borchers


Neutron reflectometry was used to study the assembly of magnetite nanoparticles in a water-based ferrofluid close to a silicon surface, Under three conditions, static, under shear and with a magnetic field, the depth profile is extracted. The particles have an average diameter of 11 nm and a volume density of 5 % in a D2O/H2O mixture. They are surrounded by a 4 nm thick bilayer of carboxylic acid for steric repulsion. The reflectivity data were fitted to a model using a least square routine based on the Parratt formalism. From the scattering length density depth profiles the following behavior is concluded: The fits indicate that excess carboxylic acid covers the silicon surface. Under constant shear the wetting layer persists but a depletion layer forms between the wetting layer and the moving ferrofluid. Once the flow is stopped, the wetting layer becomes more pronounced with dense packing and is accompanied by a looser packed second layer. In the case of an applied magnetic field the prolate particles experience a torque and align with their long axes along the silicon surface which leads to a higher particle density.
Soft Matter


neutron reflectometry, ferrofluid, colloid, Magnetic interactions, self assembly, shear, rheology


Theis-Brohl, K. , Gutfreund, P. , Vorobiev, A. , Wolff, M. , Toperverg, B. , Dura, J. and Borchers, J. (2015), Self Assembly of Magnetic Nanoparticles at Silicon Surfaces, Soft Matter, [online], (Accessed June 21, 2024)


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Created June 20, 2015, Updated October 12, 2021