Vibrationally directed assembly of micro- and nanoparticle-polymer composites

In this study, we examine directed self-assembly of micro- and nanoparticles on a vibrating substrate as a viable pathway to large-scale assembly of microstructures and composite materials. We demonstrate the vibration-driven assembly of glass bead microparticles and iron oxide nanoparticles in contact with a photocurable hydrogel (PEGDA) over an area of 3000 mm(2). The competition between acoustic radiation force and vibration-generated fluid flow in a viscous medium above a vibrating plate determines the particle transport characteristics. Based on a suspension balance model of this competition, we find that glass microparticles are dominated by displacement gradients and migrate towards displacement antinodes. Iron oxide nanoparticles that are smaller than the characteristic boundary layer generated by the flow will drive particles towards displacement nodes. We find close agreement between the observed experimental results when compared to a numerical solution to the 2D wave equation that governs this case. We also demonstrate that patterns assembled by vibration for glass microparticles or iron oxide nanoparticles dispersed in PEGDA can be immobilized by a UV light, allowing this approach to be used as a fabrication process for heterogeneously structured particle-polymer composites. The composites produced by this technique are robust and can be held by hand for application to tunable material properties for applications to bioelectronics and soft robotics. This work has been selected by the Editors as a Featured Cover Article for this issue. (C) 2018 Elsevier Ltd. All rights reserved.