Reproducible and Long-Ranged Magnetic Organization of Micropillar Arrays

The magnetically responsive organization has been explored mostly in the form of spherical magnetic particles coated with a polymer. This process is beneficial for remotely triggering chain-like organization of magnetic composites by highly penetrable magnetic fields. However, magnetic interactions often prevent the uniform and reversible organization of multiple magnetic objects. Instead, for reproducible magnetic organization, periodically arranged micropillar arrays are adopted as a geometric form of magnetic polymer composites. While the pillar base consists of magnetically inert and soft neat polydimethylsiloxane (PDMS), the pillar top is made of PDMS and highly concentrated magnetic particles. Here, the pillar base acts as the soft hinge for the reversible organization of micropillars, and the pillar top serves as a highly magnetized micro-magnet under an external magnetic field. As the magnetic field increases, adjacent two dipolar micropillars are paired by quadrupolar attractive forces. By further increasing the magnetic field, two paired micropillars are quad-assembled, and finally connectively assembled. In this presentation, we would discuss the critical magnetic field threshold for the stepwise organizations as well as parameters affecting the magnetic organization including the cross-sectional geometry of micropillars and angles of the magnetic field with respect to the micropillars.