No abstract

A novel technique for the self-assembly of three-dimensional mesoscopic structures in a forced fluid flow by employing a magnetic field is described. There are advantages of using magnetic fields for this purpose: unlike many other forces, a magnetic force is effective even from a distance, permitting “action at a distance,” it is also localized, and competition between the magnetic force and fluid shear enables unique self-assembled ferrofluid structures. Herein, a simulation provides insight into the possibility of using magnetic field to assemble colloidal nanoparticles into aggregates. Subsequently, a demonstration experiment is conducted to characterize the development and decay of such aggregates. The analysis provides a basis for developing effective self-assembly techniques for various engineering applications.

Magnetically induced accumulation and dispersion of ferrofluid in a forced flow of nonmagnetic fluid is studied experimentally and numerically to characterize the ferrofluid transport. The analysis would directly benefit several microscale and mesoscale applications like magnetic drug targeting and ferrofluid lithography. Experimental observation reveals existence of a ferrofluid core near the dipole, where the field gradient is high, and a washaway region. Numerical simulations show the ferrofluid mass flux in a similar configuration. Also, selective deposition of ferrofluid on a substrate wall exposed to a forced flow of nonmagnetic fluid is demonstrated numerically.