Design and fabrication of high power microbatteries and high specific strength cellular solids from bicontinuous microporous hierarchical materials

An emerging paradigm in engineering design is the development of materials by constructing hierarchical assemblies of simple building blocks into complex architectures that address physics at multiple length scales. These hierarchical materials are increasingly important for the next generation of mechanical, electrical, chemical, and biological technologies. However, fabricating hierarchical materials with nm control over multiple chemistries in a scalable fashion is a challenge yet to be overcome. This dissertation reports the design and fabrication of hierarchical microbattery electrodes that demonstrate unprecedented power density as well as hierarchical cellular solids with controllable modulus and high specific strength. Self-assembly, electrodeposition and microfabrication enable the fabrication of microbatteries with hierarchical electrodes. The three-dimensional bicontinuous interdigitated microelectrode architecture improves power performance by simultaneously reducing ion and electron transport distances through the anode, cathode, and electrolyte. The microbattery power densities are up to 7.4 mW cm-2 μm-1, which equals or exceeds that of the best supercapacitors and which is 2000 times higher than that of other microbatteries. A one dimensional electrochemical model of the microbatteries enables the study of physical processes that limit power performance. Lithium diffusion through the solid cathode most significantly limits the amount of energy extracted at high power density. Experimentally-validated design rules optimize and characterize the battery architecture for high power performance without the need for multiphysics based simulations. Electrochemical deposition techniques improve the microbattery energy density while maintaining high power density by allowing high volume fractions of electrochemically active material to be integrated into the high power architectures. The microbattery energy densities are up to 45.5 µWh cm-2 µm-1, which is greater than previously reported three-dimensional microbatteries and comparable to commercially available lithium-based batteries. This dissertation also demonstrates the fabrication of 3D regular macroporous microcantilevers with Young’s moduli that can be varied from 2.0 to 44.3 GPa. The porosity and deformation mode of the hierarchical material, which depends on the pore structure, determine the Young’s moduli of the microcantilevers. The template technique allows 3D spatial control of the ordered porous structure and the ability to use a broad set of materials, demonstrated with nickel and alumina microcantilevers. Self-assembly and electrodeposition enable the scaling of the hierarchical microcantilever material to areas larger than cm2. The large area nickel cellular solids have specific compressive strengths up to 0.23 MPa / (kg  m−3). The specific strength is greater than most high strength steels and titanium alloys and is due to the size strengthening effect of the nanometer scale struts in the porous architecture. The scalable fabrication and detailed characterization of the large area cellular solids provide a route for testing high strength cellular materials in a broader set of engineering applications not available to previous techniques whose material dimensions are limited to tens of micrometers

High precision electrohydrodynamic printing of polymer onto microcantilever sensors

This thesis reports electrohydrodynamic jet printing to deposit 2 ??? 27 um diameter polymer droplets onto microcantilever sensors. The polymer droplets were deposited as single droplets or organized patterns, with sub-??m control over droplet diameter and position. The droplet size could be controlled through a pulse-modulated source voltage, while droplet position was controlled using a positioning stage. Gravimetry analyzed the polymer droplets by examining the shift in microcantilever resonance frequency resulting from droplet deposition. The resonance shift of 50 - 4130 Hz corresponded to a polymer mass of 4.5 - 135 pg. The electrohydrodynamic method is a precise way to deposit multiple materials onto micromechanical sensors with greater resolution and repeatability than current methods

Computer‐Free Autonomous Navigation and Power Generation Using Electro‐Chemotaxis

Computer‐free autonomous decision making based on environmental cues provides exciting alternatives to classic control systems for robots and smart materials. Although this functionality has been studied in microswimmers and active colloids where energy in the surrounding liquid is prevalent, there are no devices that can provide sufficient power from environmental chemicals to move and steer larger scale robots and vehicles in dry environments. This work overcomes this limitation with an environmentally controlled voltage source (ECVS) that, when directly attached to electric motors on a vehicle, can increase the energy available to the vehicle and provide computer‐free autonomous navigation toward chemical fuels in the environment and away from hazards. The ECVS uses electrochemistry to extract power from the chemical fuels, and the vehicle avoids hazards that reduce the output voltage or electrochemical kinetics. Two ECVSs can also be arranged in series or parallel to perform logical functions based on the chemicals in contact with the ECVSs. This work presents a new method to simultaneously steer and power vehicles and robots without computers by directly responding to a wide variety of chemical fields in their environment using electrochemistry

Fiber Embroidery of Self-Sensing Soft Actuators

Natural organisms use a combination of contracting muscles and inextensible fibers to transform into controllable shapes, camouflage into their surrounding environment, and catch prey. Replicating these capabilities with engineered materials is challenging because of the difficulty in manufacturing and controlling soft material actuators with embedded fibers. In addition, while linear and bending motions are common in soft actuators, rotary motions require three-dimensional fiber wrapping or multiple bending or linear elements working in coordination that are challenging to design and fabricate. In this work, an automatic embroidery machine patterned Kevlar™ fibers and stretchable optical fibers into inflatable silicone membranes to control their inflated shape and enable sensing. This embroidery-based fabrication technique is simple, low cost, and allows for precise and custom patterning of fibers in elastomers. Using this technique, we developed inflatable elastomeric actuators embedded with a planar spiral pattern of high-strength Kevlar™ fibers that inflate into radially symmetric shapes and achieve nearly 180° angular rotation and 10 cm linear displacement

Towards an AI-driven soft toy for automatically detecting and classifying infant-toy interactions using optical force sensors

Introduction: It is crucial to identify neurodevelopmental disorders in infants early on for timely intervention to improve their long-term outcomes. Combining natural play with quantitative measurements of developmental milestones can be an effective way to swiftly and efficiently detect infants who are at risk of neurodevelopmental delays. Clinical studies have established differences in toy interaction behaviors between full-term infants and pre-term infants who are at risk for cerebral palsy and other developmental disorders.Methods: The proposed toy aims to improve the quantitative assessment of infant-toy interactions and fully automate the process of detecting those infants at risk of developing motor delays. This paper describes the design and development of a toy that uniquely utilizes a collection of soft lossy force sensors which are developed using optical fibers to gather play interaction data from infants laying supine in a gym. An example interaction database was created by having 15 adults complete a total of 2480 interactions with the toy consisting of 620 touches, 620 punches—“kick substitute,” 620 weak grasps and 620 strong grasps.Results: The data is analyzed for patterns of interaction with the toy face using a machine learning model developed to classify the four interactions present in the database. Results indicate that the configuration of 6 soft force sensors on the face created unique activation patterns.Discussion: The machine learning algorithm was able to identify the distinct action types from the data, suggesting the potential usability of the toy. Next steps involve sensorizing the entire toy and testing with infants

Micro architected porous material with high strength and controllable stiffness

This paper reports the engineering of large area cellular solids with controllable stiffness and specific strengths up to 230 MPa/(Mg/m(3)), which is stronger than most high strength alloys including 4143 steel and Ti-6Al-4V. The high strength arises from the size-based strengthening of the mn-sized struts. The cellular solid's porosity can be varied from 30 to 90% to control the specific stiffness from 4 - 20 GPa/(Mg/m(3)). The cellular solid's regular microporous architecture and self assembly based fabrication allow nanometer to micrometer control over the hierarchical geometry and chemistry, which enable large area materials with high strength and controllable stiffness

3D scanning coherent x-ray microscopy at PtyNAMi

X-ray ptychography in 3D is ideal for quantitative structural analysis with highest spatial resolution. The Ptychographic Nano-Analytical Microscope (PtyNAMi) installed at beamline P06 at PETRA III (DESY, Hamburg) is optimized for high-resolution scanning hard X-ray microscopy. The current data evaluation pipeline for ptychographic tomography at PtyNAMi is outlined and the performance of the microscope demonstrated at the example of an inverse opal Ni sample

First ptychographic X-ray computed tomography experiment on the NanoMAX beamline

Ptychographic X-ray computed tomography is a quantitative three-dimensional imaging technique offered to users of multiple synchrotron radiation sources. Its dependence on the coherent fraction of the available X-ray beam makes it perfectly suited to diffraction-limited storage rings. Although MAX IV is the first, and so far only, operating fourth-generation synchrotron light source, none of its experimental stations is currently set up to offer this technique to its users. The first ptychographic X-ray computed tomography experiment has therefore been performed on the NanoMAX beamline. From the results, information was gained about the current limitations of the experimental setup and where attention should be focused for improvement. The extracted parameters in terms of scanning speed, size of the imaged volume and achieved resolutions should provide a baseline for future users designing nano-Tomography experiments on the NanoMAX beamline