3D Near Field e-Writing with Submicron Resolution

Overview: The proposal aims to achieve a paradigm shift in the capabilities of the Near Field Electro-Writing (NFEW) process towards 3D hierarchical structures with submicron resolution through innovative methods of the jet’s spatial control, discharge control and material formulations. The working principal of NFEW is built upon the near-field electrospinning process which involves pulling a continuous polymer fiber from solution or melt by applying a voltage between a spinneret and a collector. Unique to NFEW, an auxiliary electrode near the spinneret is added to provide the fine control of the jet through a piezo-actuator controlled flexure manipulator; and conductive polymers will be engineered to alleviate residual charges built up in the jet to facilitate better alignment. The three PIs will combine their expertise in device engineering, machine dynamics, materials chemistry and processing, mechanics and instability analysis to analyze the fundamental process mechanics and to demonstrate the process capability that has not been seen before. Intellectual Merit: The proposed work will address two critical challenges identified for this process. First, as layers of fibers stack up, the residual charges they carry may not effectively dissipate through the collector. These charges are quasi-permanent (compared to the deposition time-scale) and will disrupt the fiber alignment through electrostatic repulsion. Second, the collector usually needs to move faster than fiber deposition rate to avoid fiber piling up and undesirable buckling. With current technological capabilities, it is very difficult to achieve sub-micron accuracy at this high speed (20 to 200 mm/s). Moreover, due to the large mass of the motion stage, the acceleration speed poses physical challenges, thus limiting changes in the direction of the deposition path. We will address these two challenges through three planned tasks. Task 1: Machine design – The essential ideas here are (1) to add an auxiliary electrode array at the point of the origin of the jet to shape the electric field and thereby the direction of the jet; (2) to use our advanced wedge-shaped motion stage to yield a tens of nano-meter resolution; and (3) to incorporate piezo-actuator and electronic regulator to achieve a precisely-controlled flow rate. Task 2: Material formulation – New material chemistries will be developed based on the hypothesis that fast discharge capability in the material is the key to alleviate many of the current hurdles for necessary resolution and accuracy of jet deposition. Conducting adducts will be engineered to known ink materials to increase electrical conductivity. In addition, new conductive glues will be explored for use as either "mortar" between layers of written structures to improve interfacial electrical and mechanical properties, or directly as "bricks" to construct functional hierarchical structures with elements across different length scales for energy applications. Task 3: Process modeling and innovation – The proposed model will include the instability analysis, fiber diameter prediction, and jet trajectory modeling. With those understandings, innovative process planning is possible, for example, the exploration of “multi-mode” process implementation to achieve a hierarchical structure by actively switching between NFEW at the sub-micron resolution level and the conventional flow-based operation at the ~20 μm resolution level. Broader impacts: If successful, 3D NFEW could create complex hierarchical structures with unprecedented ac