Question

Compare the behavior of the ferrofluid when it was in an aqueous solvent and when the solvent was changed to biodiesel. Use particulate level reasoning to explain the difference.

Answer 1

In order to prepare a ferrofluid, the magnetic particles must be very small - on the order of 10 nm (100 Å) in diameter. The thermal energy of the particles must be large enough to overcome the magnetic interactions between particles, which occurs when the particles are sufficiently small. If the particles are too large, magnetic interactions will dominate and the particles will agglomerate and precipitate. Once properly sized particles are created, they can be suspended in the liquid medium with the aid of a surfactant.

So in case of aqueus solvent, which is more polar, the thermal energy of the particle will be higher than in case of biodiesel, which is less polar.