Parallel stripes of ferrofluid as a macroscopic bidimensional smectic

An immiscible two-component mixture, made of a magnetic fluid and an organic liquid, in a Hele-Shaw cell under a magnetic field, can form different patterns like stripes or bubbles. Two-dimensional smectic-like structures are obtained with many parallel stripes. An analogy with a smectic liquid crystal allows us to define elastic moduli of the stripes. These are measured from very simple experiments. From stripe pattern energy calculation, the dependence of these elastic constants on control parameters is established. The main result is that the smectic analogy allows a rather good description of the stripe system.