The role of van der Waals forces in ferrofluid phase separation

The phase separation conditions of sterically stabilized ferrofluids are studied theoretically with major attention paid to the roles of polydispersity and van der Waals attraction. The equilibrium phase stability region is completely determined by a small number of large particles. Highly concentrated drop-like aggregates formed upon separation take up several percent of the volume of a system and account for virtually all of the large-particle fraction. Our analysis also demonstrates that van der Waals interactions play a significant role in ferrofluid phase separation; their influence is comparable to that of dipolar forces.