Magnetic Field Dependent Ordering in Ferrofluids atSiO2Interfaces

Abstract

We report pronounced smecticlike ordering in a ferrofluid adjacent to a SiO2 wall. In the presence of small magnetic fields perpendicular to the interface, ordered layers of magnetite nanoparticles form that can extend up to 30 layers. We also show that short ranged ordered structures emerge when the magnetic field direction is parallel to the interface; however, the layering is strongly perturbed. These results have been obtained by in situ neutron reflectometry which gives a detailed microscopic picture of these ordering phenomena. They also reveal the formation of a wetting double-layer which forms the magnetic template for the observed ordering sheets. The implications of these findings are discussed.

Field-induced layering of confined ferromagnetic nanoparticles: the role of attractive interactions

“…Moreover, extending the systems somewhat into the third dimension the lateral structures are supplemented by structure formation in vertical direction such as layering. This has been shown in recent experiments of ferrofluids [10] and related computer simulation studies [11,12].…”

Phase transitions and ordering of confined dipolar fluids

“…Theoretical [1][2][3], computer simulation [4][5][6][7][8][9], and experimental [10,11] studies have provided significant information about the orientational and spatial arrangement of dipolar particles in the vicinity of solid walls. The strongly anisotropic and long-ranged character of dipolar forces causes particular difficulties for the theoretical description of these systems.…”

Crystalisation of aqueous ferrofluids at the free liquid interface investigated by specular and off-specular x-ray reflectometry

“…Structure characterization of FFs in last two decades focused mainly on the organization of bulk solutions, which is well accessible via small-angle X-ray (SAXS) and neutron (SANS) scattering (e.g., see review [3,4]). At the same time, because of specific adsorption properties, the behavior of magnetic nanoparticles and surfactants in FFs at interfaces with solids and gases differs significantly from that in bulk, which is to be also considered with respect to application purposes [5][6][7]. An additional point is that a possible difference in the stability of FFs in bulk and at interfaces should be taken into account in the requirements for the stabilization of these systems with respect to their storage, namely In our previous works [8][9][10][11] we investigated the structure organization of ferrofluids at a silicon wall by neutron reflectometry.…”