Bidisperse monolayers: Theory and computer simulations

We try to elucidate the microstructure formation in a bidisperse ferrofluid monolayer and understand in detail the difference brought by the geometrical constrains. The system under study consists of soft-sphere magnetic dipolar particles confined to a thin fluid layer. The positions of the particles are constraint to a 2D geometry, whereas the particle magnetic dipole moments are not fixed to the body systems, and are free to rotate in 3 dimensions, hence forming in what we call a quasi-2D geometry (q2D). Unlike the q2D monodisperse case studied in [1] we discover that the presence of small particles inhibit ring formation. Unlike the bidisperse system in bulk thoroughly investigated in [2], small particles can form clusters and can appear in various amounts in the clusters formed by large particles. Finally we come to the conclusion, that geometrical constraints play a crucial role in determining the ferrofluid microstructure, and thus, the direct extrapolation of experimental results obtained for q2D systems to the bulk magnetic fluids might be misleading.