The Evolution of Field-Induced Structure of Confined Ferrofluid Emulsions

Abstract

We report a real-time study of the evolution of the structure of confined ferrofluid emulsions during the "liquid–solid" phase transition. A monodisperse oil-in-water ferrofluid emulsion is used. The structure evolution of the emulsion after rapidly applying a magnetic field is probed by the static light scattering. The scattering pattern exhibits pronounced rings reflecting the formation of chains and their coalescence to columns or even "worm" structures. The scattering ring is found to decrease in size and brighten in intensity with time. To monitor the structure evolution in time, both the ring peak position in scattering wavevector, q max , and the peak intensity, I max , are measured as a function of time. Both q max and I max saturate in less than 0.5 seconds after applying a magnetic field. At a constant cell thickness of 25 µm, the evolution of structure is essentially independent of volume fraction ranging from 0.015 to 0.13. In addition, a very good scaling is found in the scattered light intensity as a function of the scattering wavevector.

Colloidal force measurements in the presence of a polyelectrolyte

“…The magnitude of the magnetic dipole moment increases with the strength of the applied field until saturation has been reached. The strength of this dipolar interaction can be described by a coupling constant, which is the ratio of the contact dipole energy of two parallel dipoles to the thermal energy [16]. At low concentration, one-droplet-thick chains are well separated and oriented along the field direction.…”

The influence of magnetic field swept rate on the ultrasonic propagation velocity of magnetorheological fluids

“…This phenomenon is also caused by the complex formation of robust cluster in MR fluid. Increasing the magnetic field too quickly will give a kind of labyrinthine structure, whereas increasing the magnetic field slowly gives well separated column [15,16]. Therefore the change of ultrasonic wave velocity is rapidly altering for higher magnetic field swept rate due to this complex labyrinthine structure.…”

Forces between colloidal droplets in the presence of a weak polyelectrolyte

“…The magnitude of the magnetic dipole moment increases with the strength of the applied field until saturation is reached. The strength of this dipolar interaction can be described by a coupling constant, which is the ratio of the contact dipole energy of two parallel dipoles to the thermal energy (Mou et al 1994). At low concentration, one-droplet thick chains are well separated and oriented along the field direction.…”