Magnetically responsive polymer nanopillars with nickel cap

Embedding magnetic particles within polymer matrix is a common and facile method to fabricate magnetically responsive micro-/nanoscale pillars. However, the balance between mechanical compliance and magnetic susceptibility cannot be decoupled and the particles are limited by the pillar feature size, which can limit the actuation performance. Here we demonstrate a new type of magnetically responsive nanostructure consisting of a polydimethylsiloxane (PDMS) nanopillar array with deposited nickel caps, that has successfully achieved such decoupling with multiple cap-geometry designs for a better actuation control. The actuation result of nanopillars with 540 nm period and 1.3 μm height has been analyzed using image processing, leading to a maximum displacement of 180 nm with a ratio of 13.9% with respect to the pillar height. Magnetic and mechanical models based on magnetic force and torque have been developed and used to mitigate the weakening effect of the actuation by the residual magnetic layer. This structure demonstrates a feasible strategy for magnetic actuation at the sub-micrometer scale with freedom to design magnetic cap and polymeric pillar separately. This structure can also be utilized in multiple applications such as tunable optical elements, dynamic droplet manipulation, and responsive particle manipulation.