Fabricating ordered array of polystyrene spheres on concave structure via 3D micro-printing

Colloidal particles fabricated using lithographic methods are used in micro-nanoengineering as well as biomechanical and chemical engineering. Much of the research in this field deals with close-packed colloidal particles in the form of continuous two-dimensional (2D) surface structures or membranes. The most common approach to modifying the arrangement and spacing of colloidal particles involves etching or the fabrication of micro-nanoimprinted structures at the micro- or nanoscale. In the current study, three-dimensional (3D) micro-printing was used to fabricate grid and honeycomb structures with precise control over the spatial distribution and height. We achieved a uniform distribution of polystyrene micro spheres across the surface of the structures by performing a variation of the floating assembly method referred to as drop deposition, which when implemented using methanol was shown to enhance the dispersal of microspheres in the mixture by reducing the London diverse force (LDF). The application of ultrasonic vibrations during microsphere deposition was shown to facilitate the integration of PS microspheres within the underlying lattice. We also found that methanol is highly effective in the removal of accumulated microspheres. The fabrication of grid and hexagonal structures spaced at intervals of 6, 6.5, and 7 μm followed by the deposition of PS microspheres (diameter = 6 μm) was shown to increase the water droplet contact angle from 103° (close-packed) to 110° (square arrangement) and 123° (hexagonal arrangement).