Light polarization using ferrofluids and magnetic fields

Alberto TufaileAdriana Pedrosa Biscaia Tufaile

Soft Matter LaboratoryEscola de Artes, Ciências e Humanidades

Universidade de São Paulo

Introduction• When a strong magnet is brought close to the ferrofluids

(Ferrocell), there is a pattern formation, because the external magnet changes the shape of the nanoparticles, and the magnetic nanoparticles arrange themselves in complex geometries in ferrofluids, such as labyrinth or needles, due to the long range dipolar interactions. One way to observe these complex geometries is using polarized light.

Ferrocell USA

What is a Ferrocell? It is a Hele-Shall cell containing ferrofluid. Ferrofluid is a colloid containing surfactant coated nanometer particles dispersed in a carrier liquid.

Ferocell was created by Timm A. Vanderelli, owner of the company

Experimental Apparatus: Ferrocell

Polarizers with Ferrocell.

... And Hall sensor (Gaussmeter)...

...And Magnets (Geometry)The magnets used are neodymium rare earth magnets (Amazing Magnets) grade N40/N45 NdFeB.

Functions of Magnetic Field

Magnet and Field: Unipolar and Bipolar: 3D

Unipolar cofiguration

Cube and its motion

Cylinder Experiment Simulation

Bipolar & Tetrapolar

Experiment Simulation

Hall sensor

Bipolar and Tripolar configuration

Two cylinders, side by side.

Experiment

Simulation

Analogy

Using the magnetic field of a disc.

Experiment Simulation

Image of ferrofluid needles• Image: 400 x ;• 100 G < B < 500 G

R

R+a

Ferrofluid is a colloid containing surfactant coated nanometer particles dispersed in a carrier liquid.

‘Acting’ like nanocompass

Analysis of unipolar configuration:

Analogy with Hermite-Gauss Polynomials

m=1, n=1

Comparing with Hall sensor

Axially-symmetric Sheared Structure

The pretilt angle explains why the central spot appears dark under crossed polarizers: axially-symmetric sheared structure.

Concluding remarks• One potential application is characterizing and

controlling the quality of permanent magnets, which are never perfectly magnetized;

• Fast analysis of the magnetic field distribution of small multipolar magnets and magnetic assemblies;

MagCam... Another visualization option.

And more...• The pattern formation curiously resembles the nodal lines of the

transverse electric and magnetic modes observed in optical resonant cavities, explained by hypergeometric polynomials, such as Hermite-Gauss, Laguerre-Gauss and Ince-Gauss polynomials.

• In this analogy the magnetic field has an equivalent role of the gaussian irradiance distribution, and the light source is very flat lamp nearly normal to z, which nearly corresponds to a plane wave with constant flux set up along the z-axis, analogous to a standing wave in the optical resonant cavity.

For the future:• To study the

Faraday effect, dichroism, and birefringence.

Two crossed laser beams in a Ferrocell with a magnet behind it, no polarizers here. The ferrofluid particles are scattering light forming curved structures.

ACKNOWLEDGMENTS• This work was supported by Conselho Nacional de

Desenvolvimento Científico e Tecnológico (CNPq), Instituto Nacional de Ciência e Tecnologia de Fluidos Complexos (INCT-FCx) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), FAPESP/CNPq #573560/2008-0.

• Timm A. Vanderelli for the Ferrocells, discussions and suggestions about this device, and Michael Snyder. These two guys rocks! Thank you.