Printable energy storage is anticipated to facilitate innovation in the manufacture of flexible electronics and soft robotics by enabling direct integration of a power source into a system during the ...fabrication process. To this end, we have established a universal approach to develop 3D printable, free-standing electrodes with an embedded current collector for high-performance Li-ion batteries. This simple approach utilizes a well-dispersed mixture of active material, carbon nanofibers, and polymer to make castable or printable electrode inks. By tuning the ratios of these components in a series of inks, we have observed the effect each parameter had on the resulting rheological, electrochemical, and mechanical properties. Once properly balanced, free-standing electrodes of three common Li-ion battery active materials (i.e., lithium titanate (Li4Ti5O12), lithium iron phosphate (LiFePO4), and lithium cobalt oxide (LiCoO2)) were prepared, each demonstrating excellent cyclability and rate capability. Finally, electrodes were successfully patterned using a direct ink writing method, and a fully-printed, working electrode plus separator electrode assembly were developed.
Liquid crystalline elastomers (LCEs) are widely recognized for their exceptional promise as actuating materials. Here, the comparatively less celebrated but also compelling nonlinear response of ...these materials to mechanical load is examined. Prior examinations of planarly aligned LCEs exhibit unidirectional nonlinear deformation to mechanical loads. A methodology is presented to realize surface‐templated homeotropic orientation in LCEs and omnidirectional nonlinearity in mechanical deformation. Inkjet printing of the homeotropic alignment surface localizes regions of homeotropic and planar orientation within a monolithic LCE element. The local control of the self‐assembly and orientation of the LCE, when subject to rational design, yield functional materials continuous in composition with discontinuous mechanical deformation. The variation in mechanical deformation in the film can enable the realization of nontrivial performance. For example, a patterned LCE is prepared and shown to exhibit a near‐zero Poisson's ratio. Further, it is demonstrated that the local control of deformation can enable the fabrication of rugged, flexible electronic devices. An additively manufactured device withstands complex mechanical deformations that would normally cause catastrophic failure.
The synthesis of liquid crystal elastomers (LCEs) in the homeotropic orientation enables omnidirectional nonlinearity in mechanical deformation. Locally directing the self‐assembly of the orientation of the LCEs generates films of continuous composition but spatially distinguished mechanical responses. Local control of the mechanical deformation of the LCEs has functional benefits in realizing near‐zero Poisson's ratio or by ruggedizing flexible electronic devices.
Polyimides are widely utilized engineering polymers due to their excellent balance of mechanical, dielectric, and thermal properties. However, the manufacturing of polyimides into complex ...multifunctional designs can be hindered by dimensional shrinkage of the polymer upon imidization and post processing methods and inability to tailor electronic or mechanical properties. In this work, we developed methods to three-dimensional (3D) direct ink write polyimide closed-cell stochastic foams with tunable densities. These polyimide structures preserve the geometrical fidelity of 3D design with a linear shrinkage value of <10% and displayed microscale porosity ranging from 25 to 35%. This unique balance of morphology and direct-write compatibility was enabled by polymer phase inversion behavior without the need of conventional post-print cross-linking, imidization, or pore-inducing freeze processing. The manufacturability, thermal stability, and dielectric properties of the 3D polyimide stochastic foams reported here serve as enablers for the exploration of hierarchical, lightweight, high-temperature, high-power electronics.
Elastic metastructures provide advanced control of elastic wave propagation, particularly through their ability to exhibit frequency band gaps where elastic waves cannot propagate. Several ...metastructure design strategies to realize band gaps in frequency ranges of interest have emerged in recent years. However, the band gap frequencies are fixed at design time by the metastructure geometry and constituent materials. Here, a tunable metamaterial is developed which utilizes the coupled magneto-mechanical response of magnetoactive elastomers (MAE) to enable active control of the band gap frequencies. It is shown that the band gap of a lattice-based metastructure design can be tuned over a continuous frequency range by remote application of a magnetic field. A direct-ink write fabrication method is introduced to fabricate the metastructures from MAEs, which allows this concept to be extended to a vast design space. Our results suggest that the band gap tunability depends not only on the strength of the applied magnetic field, but also on the interaction of the magnetic field and the metastructure geometry. This implies that the combined effects of geometry and magnetic stiffening represent a new design parameter for tunable metastructures, enabling the creation of new smart structures which feature tunable inherent vibration control.
Optical microscopy images and confocal data for Aerosol Jet Printed (AJP) lines over a 16 hour print duration is provide in this dataset (“Mapping Drift in Morphology and Electrical Performance in ...Aerosol Jet Printing” 1). Lines were uninterruptedly printed by AJP on a glass substrate using silver nanoparticle ink over a 16-hour time frame. The ink used for this experiment was a 0.6:0.3:0.2 mL mixture of Clariant Prelect TPS 50 G2 silver nanoparticle ink, ethylene glycol, and deionized water, respectively. Deposition was achieved with an Optomec AJ 300-UP Aerosol JetTM Deposition System using a Sprint Series Ultrasonic Atomizer MAX, aerodynamic filtering, and a nozzle having an orifice diameter of 150 µm. The typical focus ratio of 1.75 within standard range was used. The optical microscopic images of 350 µm AJP printed lines at 80 different time points were then selectively collected. Keyence VK-X200 with 150x magnification was used, which provided 50 µm to 267 pixel resolution image with more than 1000 cross-sections at each time point. Filtering of the pixels with outlying heights was performed with a multi-file analyzer. The dataset was primarily collected to understand system-level, temporal drifts in print morphology, which would further allow to predict electrical performance in time domain. Additional purposes for the dataset include: 1) benchmark dataset for morphology and print performance between AJP systems and print settings, 2) test data for new image filtering, segmentation, and classification algorithms and 3) baseline training data for real-time, in situ classification of operational time windows for AJP feedback control.
In fabricating electronic components or devices via Aerosol Jet Printing (AJP) there are numerous options for commercially available Metal NanoParticle (MNP) inks. Regardless of the MNP ink selected, ...the electrical properties of the final product are not commensurate to those of the bulk metal due to the inherent porosity and impurity-infused composition that is characteristic of these heterogeneous feedstock. Hence, choosing the best MNP ink for a particular application can be difficult, even among those based on the same metal, as each ink formulation can yield different performance metrics depending on the specific formulation and the conditions under which it is processed. In this article, the DC conductivity of AJP pads and the Radio Frequency (RF) transmission loss of AJP Coplanar Waveguides (CPWs) are presented for three different, commercially available silver MNP inks; Advanced Nano Products (ANP) Silverjet DGP 40LT-15C, Clariant Prelect TPS 50 G2, and UT Dots UTDAg40X. We determined conductivity values by measuring the printed pad thicknesses using stylus profilometry and measuring sheet resistances using a co-linear 4-point probe. Additionally, we collected RF spectra using a performance network analyzer over the 10 MHz – 40 GHz range. A complete description of the preparation, AJP procedure, and sintering is provided. Conductivity and RF data are presented for several scenarios including sintering temperatures, sintering atmospheres, and un-sintered storage conditions. We anticipate this dataset will serve as a useful reference for benchmarking electrical performance and troubleshooting pre- and post-processing steps for Ag nanoparticle based AJP inks.
Tandem solar cell architectures are designed to improve device photoresponse by enabling the capture of wider range of solar spectrum as compared to single-junction device. However, the practical ...realization of this concept in bulk-heterojunction polymer systems requires the judicious design of a transparent interconnecting layer compatible with both polymers. Moreover, the polymers selected should be readily synthesized at large scale (>1 kg) and high performance. In this work, we demonstrate a novel tandem polymer solar cell that combines low band gap poly isoindigo P(T3-iI)-2, which is easily synthesized in kilogram quantities, with a novel Cr/MoO3 interconnecting layer. Cr/MoO3 is shown to be greater than 80% transparent above 375 nm and an efficient interconnecting layer for P(T3-iI)-2 and PCDTBT, leading to 6% power conversion efficiencies under AM 1.5G illumination. These results serve to extend the range of interconnecting layer materials for tandem cell fabrication by establishing, for the first time, that a thin, evaporated layer of Cr/MoO3 can work as an effective interconnecting layer in a tandem polymer solar cells made with scalable photoactive materials.
Direct ink writing, an extrusion‐based 3D printing method, is well suited for high‐mix low‐volume manufacturing. However, an iterative approach, using random selection or constant expert guidance, is ...still used to create printable inks and optimize printing parameters by expending significant amounts of time, materials, and effort. Herein, a machine learning (ML) model that estimates ink rheology in‐situ from a simple printed test pattern is reported. This ML model is trained with a rheologically diverse set of inks composed of different polymers. The model successfully correlated features of the simple printed test pattern to rheological properties, which could, in theory, inform both printed structures and future ink compositions. The behavior of this model is verified and analyzed with explainable artificial intelligence tools, linking printed feature importance to one's known physical understanding of the process.
High mix, low volume processes such as additive manufacturing (AM) offer tremendous promise for increasing the customization in manufacturing but are hindered by the lack of efficient methods for ...identifying process parameters for complex new geometries exhibiting the desired performance. The search over the process space can be automated with analysis tools that can be applied in a time and resource efficient manner such that ambitious print designs are not dissuaded by the cost of process parameter discovery. In this work, we propose an image analysis tool that can classify spanning prints as one of five process-relevant archetypes, invariant of the span dimensions. We describe a modular design of the tool such that simple adjustments to image processing parameters allow for compatibility with different print processes and environments. Furthermore, we demonstrate how this tool may be incorporated into a fully automated workflow on multiple AM systems to facilitate rapid autonomous process parameter discovery and/or deeper scientific understanding.
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Template-free 3D printing of electronic devices has the potential to broaden electronics integration to include complex integrated form factors, but success requires precise, adaptive ...control over materials processing. The development of such manufacturing technologies requires exploration of new combinations of ink sets, printing techniques, and automation strategies. In this work, solution-cast direct-write (SC-DW) was used to print poly(methyl methacrylate) (PMMA) dielectric films with breakdown fields of 790 V/μm, similar to commercially available biaxial-oriented polypropylene (BOPP) films. Furthermore, a complementary composite ink for printing conductive features was developed with conductivities of ˜10,000 Scm-1. A closed-loop feedback system that links deposition parameters with characterization was necessary to maintain μm-precision deposition for over 20 h without human involvement. This closed-loop control scheme enabled 3D printing of both single- and double-layer high-voltage capacitors with capacitances as large as 314 pF (at 1 kHz) and breakdown voltages over 1000 V, which is significant step towards repeatable template-free, 3D printing of electronics for rapid prototyping of multifunctional devices. The precise control over low minimum feature dimension, high breakdown voltage, and long print duration enables the exploration of a broader range of printed electronics application than conventional 3D printing techniques.
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