Integrated pumps and valves make up an essential part of most microfluidic devices and produce increased control in the device. Some existing micro-pumps and valves utilized in microfluidics involve electrical, pneumatic, and thermal actuation. However, electrical micro-pumps and valves generally entail a complicated and expensive fabrication process, and are limited to samples free of any ions...

We explore magnetic-field-induced ordering and microphase separation of aqueous ferrofluid and of aqueous mixtures of ferrofluid with nonmagnetic latex spheres. The ferrofluid is a surfactant stabilized aqueous suspension of magnetite (Fe3O4) particles with average diameter 20 nm (including the approximately 2.5-nm thick surfactant layer); the nonmagnetic latex spheres are charge stabilized pol...

We report on the fabrication and characterization of a single-mode fiber variable optical attenuator (VOA) based on a ferrofluid shutter actuated by a magnetic field created by a low voltage electromagnet. We compare the performance of a VOA using oil-based ferrofluid, with one VOA using water-based 12 ferrofluid, and demonstrate broadband optical attenuation of up to 28 dB with polarization de...

Ferrofluid spin-up flow is studiedwithin a sphere subjected to a uniform rotatingmagnetic field from two surrounding spherical coils carrying sinusoidally varying currents at right angles and 901 phase difference. Ultrasound velocimetry measurements in a full sphere of ferrofluid shows no measureable flow. There is significant bulk flow in a partially filled sphere (1–14 mm/s) of ferrofluid or ...

We describe a convective instability of a stratified ferrofluid subject to a magnetic field. The ferrofluid is described as binary mixture featuring two important dimensionless numbers the barometric one B and the magnetic barometric one Bm. At the field strength, where the latter exceeds the former, instability sets in. We discuss the growth rate of linear perturbations and the amplitude of no...

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (γ-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by...

2014 We have observed the surface instability of the interface between a highly concentrated ferrofluid and a weakly concentrated one. Our experimental data clearly show the first order character of the transition between a flat interface and the observed regular pattern of peaks. A large hysteresis effect is observed because of the high value of the relative permeability (03BC ~ 40) of our con...

The viscosity n of Fe,O, ferrofluid at volume concentrations in the range t = 0.0-0.013 are measured. The corresponding range of values of q is 1.6-1.8 cp. A linear relationship exists between the relative viscosity and the concentration of the fluid. Measurements of relative resistivity of Fe,O, ferrofluid at various concentrations (E = 0.00526-0.0526) are also reported. The relative resistivi...

A novel micromixer which utilizes chaotic mixing induced by ferrofluid actuation is developed. The micromixer is fabricated by a polydimethylsiloxane micromolding technique. The micromixer consists of a T-shaped main mixing channel and two parallel sub-channels that intersect the main channel. Oscillation of a couple of ferrofluid slugs in the sub-channels, induced by external permanent magnet ...

We present a new method for the determination of the magnetic moment distribution ρ(μ) of ferrofluid particles from the magnetization curve measured on diluted ferrofluid samples in the liquid state. The method employs the solution of the standard integral equation describing the magnetization of a non-interacting particle system in the given external field as a convolution of the Langevin func...