Nanodroplet Flight Control in Electrohydrodynamic Redox 3D Printing.

Electrohydrodynamic 3D printing is an additive manufacturing technique with enormous potential in plasmonics, microelectronics, and sensing applications thanks to its broad material palette, high voxel deposition rate, and compatibility with various substrates. However, the electric field used to deposit material is concentrated at the depositing structure, resulting in the focusing of the charged droplets and geometry-dependent landing positions, which complicates the fabrication of complex 3D shapes. The low level of concordance between the design and printout seriously impedes the development of electrohydrodynamic 3D printing and rationalizes the simplicity of the designs reported so far. In this work, we break the electric field centrosymmetry to study the resulting deviation in the flight trajectory of the droplets. Comparison of experimental outcomes with predictions of an FEM model provides new insights into the droplet characteristics and unveils how the product of droplet size and charge uniquely governs its kinematics. From these insights, we develop reliable predictions of the jet trajectory and allow the computation of optimized printing paths counterbalancing the electric field distortion, thereby enabling the fabrication of geometries with unprecedented complexity.

Pixelated Physical Unclonable Functions through Capillarity-Assisted Particle Assembly.

Recent years have shown the need for trustworthy, unclonable, and durable tokens as proof of authenticity for a large variety of products to combat the economic cost of counterfeits. An excellent solution is physical unclonable functions (PUFs), which are intrinsically random objects that cannot be recreated, even if illegitimate manufacturers have access to the same methods. We propose a robust and simple way to make pixelated PUFs through the deposition of a random mixture of fluorescent colloids in a predetermined lattice using capillarity-assisted particle assembly. As the encoding capacity scales exponentially with the number of deposited particles, we can easily achieve encoding capacities above 10700 for sub millimeter scale samples, where the pixelated nature of the PUFs allows for easy and trustworthy readout. Our method allows for the PUFs to be transferred to, and embedded in, a range of transparent materials to protect them from environmental challenges, leading to improved stability and robustness and allowing their implementation for a large number of different applications.