title: Viscoelasticity of mono- and polydisperse inverse ferrofluids.
abstract: We report on measurements of a magnetorheological model fluid created by dispersing nonmagnetic microparticles of polystyrene in a commercial ferrofluid. The linear viscoelastic properties as a function of magnetic field strength, particle size, and particle size distribution are studied by oscillatory measurements. We compare the results with a magnetostatic theory proposed by De Gans et al. [Phys. Rev. E 60, 4518 (1999)] for the case of gap spanning chains of particles. We observe these chain structures via a long distance microscope. For monodisperse particles we find good agreement of the measured storage modulus with theory, even for an extended range, where the linear magnetization law is no longer strictly valid. Moreover we compare for the first time results for mono- and polydisperse particles. For the latter, we observe an enhanced storage modulus in the linear regime of the magnetization.
authors.affiliation: Centro de Investigación en Química Aplicada, 25100 Saltillo, Coahuila, México.
authors.forename: Ruben
authors.initials: R
authors.lastname: Saldivar-Guerrero
authors.forename: Reinhard
authors.initials: R
authors.lastname: Richter
authors.forename: Ingo
authors.initials: I
authors.lastname: Rehberg
authors.forename: Nuri
authors.initials: N
authors.lastname: Aksel
authors.forename: Lutz
authors.initials: L
authors.lastname: Heymann
authors.forename: Oliverio S
authors.initials: OS
authors.lastname: Rodriguez-Fernández