Structurization of ferrofluids in the absence of an external magnetic field

Abstract

Abstract-Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well known laboratory experiments and computer simula tions in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first order phase transition.

Branching points in the low-temperature dipolar hard sphere fluid

“…21 At low temperature T and density ρ, dipolar particles tend to form chain-like structures, 16,22 giving rise to a fluid made up of long, transient, and weakly interacting chains (structures in which all particles, except two, have two neighbours aligned in the nose-to-tail configurations) and rings (structures in which all particles are doubly bonded). 18,23,24 As the density increases, inter-cluster interactions start to rise and, eventually, chains and rings merge together to form branched clusters [25][26][27][28] via the emergence of junctions, i.e., of particles which have more than two neighbours. The analysis of equilibrium configurations confirms that, for any reasonable criterion for classifying two neighbour particles as bonded, a significant number of branching points exists, 15,18 providing a mechanism for connecting chains and rings in a percolating three-dimensional network.…”