Sadaf Sobhani

Abstract The performance of electrospray thrusters is limited by the precision and constraints of traditional emitter fabrication techniques, which often lack resolution, geometric flexibility, or material compatibility for optimal emitter design and fabrication. Here, we demonstrate a high-resolution additive manufacturing approach for fabricating monolithic fused-silica electrospray emitters using two-photon polymerization (TPP) printing followed by thermal conversion. Triply-periodic-minimal-surface (TPMS) microporous structures were embedded within the emitter body to provide passive capillary transport of propellant to the emitter tip. Optical profilometry and electron microscopy confirm high geometric fidelity to the target design and uniform shrinkage of approximately 40% during thermal processing, with preservation of the TPMS architecture. Electrospray emission testing was performed with ionic liquid EMI-BF4 propellant, which showed stable and repeatable emission with onset voltages of 2.4 - 2.6 kV, linear current-voltage characteristics, and high single emitter thrust of 64 nN at specific impulse values exceeding 3000 s. These results establish TPP-printed fused-silica emitters with integrated TPMS architectures as a robust and versatile platform for scalable electrospray propulsion systems.

Pressure-driven infiltration in capillary-opposed microchannels is commonly controlled through surface chemistry, while the role of channel geometry remains less understood. Here, we show that sinusoidal channel profiles can regulate liquid advancement by creating periodic capillary barriers that produce stepped meniscus motion under an applied pressure. We develop an analytical force-balance model that incorporates applied pressure, capillary forces, and viscous dissipation to predict conditions for interface advancement and arrest. High-speed synchrotron X-ray radiography of enclosed three-dimensional (3D)-printed microchannels confirms the predicted qualitative behavior, including successive arrest and release events during filling. Because the native printed material is near-neutral in wettability and does not sustain capillary-opposed flow, a conformal iCVD fluoropolymer coating was used to increase the contact angle to about 106°. Together, the model and experiments show that channel geometry can be used to tune pressure-driven infiltration independently of surface chemistry, establishing a geometric strategy for passive flow regulation in microfluidic systems.

Pressure-driven infiltration in capillary-opposed microchannels is commonly controlled through surface chemistry, while the role of channel geometry remains less understood. Here, we show that sinusoidal channel profiles can regulate liquid advancement by creating periodic capillary barriers that produce stepped meniscus motion under an applied pressure. We develop an analytical force-balance model that incorporates applied pressure, capillary forces, and viscous dissipation to predict conditions for interface advancement and arrest. High-speed synchrotron X-ray radiography of enclosed three-dimensional (3D)-printed microchannels confirms the predicted qualitative behavior, including successive arrest and release events during filling. Because the native printed material is near-neutral in wettability and does not sustain capillary-opposed flow, a conformal iCVD fluoropolymer coating was used to increase the contact angle to about 106°. Together, the model and experiments show that channel geometry can be used to tune pressure-driven infiltration independently of surface chemistry, establishing a geometric strategy for passive flow regulation in microfluidic systems.

Solid oxide electrolysis cells (SOECs) suffer from interfacial delamination that limits long-term durability. Most studies of this process rely on post-mortem techniques, which cannot capture how delamination develops in real time. In this work, we demonstrate the use of synchrotron X-ray radiography to monitor thermal-cycling-induced delamination in SOECs. A custom fixture and cell design were developed to meet synchrotron constraints while maintaining operability. Transmission profiles extracted from radiographs revealed systematic changes at the air electrode-electrolyte interface during cycling, consistent with progressive delamination. Post-mortem X-ray computed tomography confirmed interfacial separation, supporting the interpretation of the radiographs. A physics-based attenuation model was used to simulate delamination, and the predicted transmission profiles reproduced the main experimental features. This combined experimental and modeling approach establishes a framework for quantifying interfacial degradation during accelerated testing and provides a path toward operando reliability studies of SOECs.

This study investigates the use of binary ionic liquid (IL) mixtures as advanced heat transfer fluids, with the aim of identifying combinations that exhibit improved thermophysical properties compared to their pure IL components. The focus is on predicting viscosity using machine learning (ML) models enhanced with physics-based descriptors. Thermophysical property data were collected for 698 binary mixtures, alongside extensive pure IL datasets used for reference. Multiple feature-generation strategies were explored to represent binary systems, including ideal mixing rules for conventional molecular descriptors to capture composition-dependent interactions, as well as quantum chemical surface charge densities and chemical potentials to incorporate structure-dependent realistic interactions. Initial analysis shows non-ideal behavior in viscosity with respect to both temperature and mole fraction, supporting the potential of binary systems to offer more favorable properties. Deep neural networks were developed for pure ILs and mixtures, and feature reduction techniques were applied to identify the most informative structural and energetic descriptors. This work provides a foundational step toward a generalizable ML framework for predicting binary IL behavior and supports future data-driven design of IL mixtures for single-phase thermal control loops, particularly for aerospace applications in extreme environments.

Introduction Solid oxide electrolysis cells (SOECs) are a promising high-temperature electrochemical energy conversion technology for carbon dioxide reduction, hydrogen production, or co-electrolysis. However, their commercialization remains limited due to performance degradation over mid- to long-term operation. This degradation, often characterized by increased area-specific resistance, overpotential, or polarization losses, is primarily caused by structural changes within the cells, particularly delamination at the electrode-electrolyte interface [1,2]. An increasing number of studies have sought to characterize the mechanisms leading to delamination. Delamination at the fuel electrode-electrolyte interface is often attributed to thermal expansion coefficient (TEC) mismatch [3], while delamination at the air electrode-electrolyte interface arises when oxygen partial pressure exceeds the bond strength between layers [2]. Prior studies have explored the onset conditions for delamination and its impact on electrochemical performance, but delamination is not a binary phenomenon. Instead, its quantification and progression modeling are essential for predicting the remaining operational life of SOECs [4]. While laboratory and synchrotron-based X-ray sources have been used to study porosity, grain boundaries, crystallography, and material phases in SOECs—both in situ and ex situ—there remains a gap in connecting structural changes to electrochemical performance quantitatively. To bridge this gap, this work explores the use of absorption contrast radiography, statistical analysis, and machine learning to quantify in-situ delamination of SOECs. Experimental Methods Experiments are conducted on operationally relevant-sized SOECs at the Forming and Shaping Technology (FAST) beamline of the Cornell High Energy Synchrotron Source (CHESS) at an energy of 70 keV and detector resolution of 1.5 μm per pixel. The cell consists of a nickel oxide (NiO) - 8 mol% yttria-stabilized zirconia (8YSZ) cermet cathode, an 8YSZ electrolyte, a gadolinium-doped ceria (GDC) barrier layer, and a lanthanum strontium cobaltite (LSC) anode, with layer thicknesses of approximately 400 μm, 3 μm, 3 μm, and 12 μm, respectively. As a proxy for electrochemically induced delamination, samples are subjected to accelerated thermal cycling to induce delamination, which is captured in situ using X-ray radiography. Previous studies have shown that Ni-YSZ/YSZ half-cells experience delamination due to TEC mismatch, a phenomenon that is amplified in full cells since the LSC anode exhibits an even greater TEC mismatch with YSZ than the Ni-YSZ electrode [2,5]. Quantification of Delamination To quantify delamination, the electrolyte layer is segmented, and an region of interest (ROI) is selected around the interface to track delamination between the electrolyte and adjacent layers. Since the radiograph represents a 3D structure in a 2D projection, a probability density function (PDF) of pixel intensities within the ROI is extracted to statistically capture changes in absorption caused by delamination. As delamination progresses, affected pixels exhibit higher intensity values due to reduced material attenuation, shifting the PDF. This shift typically manifests as a decrease in the primary peaks and the appearance of new high-intensity values To establish a baseline for quantification, a series of artificially delaminated reference images are generated using a Beer-Lambert law formulation applied to virgin samples. The approach involves simulating various delamination geometries, including horizontal (aligned with the electrode-electrolyte interface), diagonal, and irregular delamination accounting for surface roughness. Two-dimensional radiographs are converted into a three-dimensional space to model variations in the linear attenuation coefficient along the beamline direction. A pixelwise local attenuation coefficient is computed using Beer-Lambert law, then modified to account for air-filled regions in delaminated areas. The result is a library of PDFs corresponding to different delamination scenarios. Once the PDFs for all likely delamination scenarios are established, the experimentally captured in-situ PDFs are analyzed to quantify delamination progression. A Gaussian process regression (GPR) based machine learning model is trained to match the in-situ PDFs to the precomputed artificial delamination PDFs, resulting in quantification of the delamination. Implications and Future Applications This framework, initially applied to thermally induced delamination, can be directly applied to electrochemically-induced delamination without modifying the imaging or analysis methodology. Currently, delamination progression is mapped to heating rate and cycle count, but applying this method to operando SOECs would provide insight into how delamination evolves in response to electrochemical performance metrics. Conclusion This work presents a novel quantification framework for in-situ delamination analysis in SOECs, leveraging synchrotron-based X-ray radiography, statistical modeling, and machine learning. By developing a method to statistically and computationally quantify delamination, this approach lays the foundation for predicting SOEC lifetime and establishing structure-performance correlations, ultimately contributing to the commercial viability of SOEC technology. References [1] Y. Wang, et al., J. Mat. Sci & Tech., 55 , 35-55 (2020). [2] B. Park, et al., Energy Environ. Sci ., 12 , 3053-3062 (2019). [3] T. M. M. Heenan, et al., J. Electrochem. Soc., 165, F932 (2018). [4] W. K. S. Chiu, et al. Materials Today , 80 , 481-496 (2024). [5] V. Vibhu, et al., J. Electrochem. Soc., 166 , F102 (2019). Acknowledgements: Research supported by TotalEnergies Office of Sponsored Projects (#163944). This work is based upon research conducted at the Center for High Energy X-ray Sciences (CHEXS), which is supported by the National Science Foundation [DMR-1829070].

High-resolution electronic tactile displays stand to transform haptics for remote machine operation, virtual reality, and digital information access for people who are blind or visually impaired. Yet, increasing the resolution of these displays requires increasing the number of individually addressable actuators while simultaneously reducing their total surface area, power consumption, and weight, challenges most evidently reflected in the dearth of affordable multiline braille displays. Blending principles from soft robotics, microfluidics, and nonlinear mechanics, we introduce a 10-dot-by-10-dot array of 2-millimeter-diameter, combustion-powered, eversible soft actuators that individually rise in 0.24 milliseconds to repeatably produce display patterns. Our rubber architecture is hermetically sealed and demonstrates resistance to liquid and dirt ingress. We demonstrate complete actuation cycles in an untethered tactile display prototype. Our platform technology extends the capabilities of tactile displays to environments that are inaccessible to traditional actuation modalities.

Recent advances in the photocatalytic activation of dry reforming of methane (DRM: CO 2 + CH 4 → 2CO + 2H 2 ) at low temperature and ambient pressure have generated considerable interest as a promising route to convert greenhouse gases into valuable synthetic gas (syngas). While detailed studies have revealed the mechanisms involved in photocatalytic DRM at metal–semiconductor interfaces, less attention has been devoted to how high-surface-area semiconductor supports may enhance such conversions. Here, we structure triblock terpolymer self-assembly directed sol–gel-derived transition metal oxide (Ta 2 O 5 or TiO 2 ) supports of Rh-loaded photocatalysts into various equilibrium and nonequilibrium derived porous morphologies and show how they modulate single-pass conversion, total production rate, and material efficiency. Supported by in-depth materials characterization, flow, and optics simulations rationalizing observed trends, results reveal record catalyst performance. Our work suggests that asymmetric pore structures simultaneously optimizing mass transport and surface area may be well-suited to maximize photocatalyst performance.

This study utilizes deep neural networks and random forests to predict the thermophysical properties of ionic liquids (ILs), focusing on viscosity and liquid phase transition temperature (LPTT) at atmospheric pressure. The goal is to identify novel ILs with superior properties for spacecraft thermal control, surpassing current heat transfer fluids. Two curated datasets were employed: 1,139 ILs for viscosity predictions, incorporating temperature and 210 molecular descriptors as features, and 1,458 ILs for LPTT predictions with 210 molecular descriptors. The study explores various training-test split strategies and model configurations to optimize predictive performance. These optimized models were then applied to predict the properties of 328,740 generated IL permutations, targeting low viscosity and LPTT values below 243 K. This work provides a scalable framework for designing high-performance ionic liquids, contributing to the development of advanced thermal management systems for extreme environments.

Traditional low-temperature and high-temperature heat pipes dominate existing thermal control systems, but a significant gap persists in addressing thermal rejection efficiency within the intermediate-temperature range. Ceramics, with their exceptional chemical and thermal stability, offer compatibility with a broad range of working fluids, making them uniquely suited to bridge this gap. This work presents a novel experimental study of additively manufactured (AM) ceramic heat pipes. Grooved alumina envelopes were fabricated and tested with ethanol and Dowtherm A. Mass rate-of-rise experiments were conducted to quantify the effects of silicate glaze coatings on permeability and effective pore radius. Atmospheric heat pipe testing exhibited stable isothermal behavior under a heat flux of up to 5.65 W across the adiabatic section. These findings establish a foundation for leveraging AM ceramic technologies to enhance spacecraft thermal management.

Liquid halides have been identified as promising working fluids for heat pipes operating in the intermediate temperature regime of 500-750 K. However, their compatibility with conventional heat pipe envelope materials remains limited. Ceramic heat pipes have been proposed as a solution, enabling compatibility with halide fluids while leveraging additive manufacturing for advanced topological designs. The design of aluminum nitride (AlN) heat pipes in the context of spacecraft radiators is analyzed, using aluminum bromide (AlBr3) as the working fluid. A 1D thermal model of the combined radiator and heat pipe assembly is presented, optimized globally to achieve an areal density below 3 kg/m^2 while maintaining 70% radiator efficiency. This optimization yields a power density of 5 kW/m^2 and a heat rejection specific mass of 0.47 kg/kW. A range of potential designs is proposed, highlighting the refinement opportunities provided by additive manufacturing.

The dynamics of capillary rise under different geometric and fluid conditions have the common signatures of rapid rise followed by an equilibrium state that describe the underlying competing forces. We present a new interpretation of capillary dynamics using a linear damped system where modulation of damping and forcing characteristics are achieved using axisymmetric channels with sinusoidal variation in radius. The complete axisymmetric design space ranging from hydrophilic channels that enable spontaneous imbibition to hydrophobic channels, that required external pressure mechanisms is modeled and the force dynamics is split into simultaneous damping and forcing characteristics. We introduce the product of damping and forcing terms as the new parameter that effectively characterizes rise dynamics across various geometric and flow conditions, encompassing both flow-enhancing and flow-inhibiting scenarios. The monotonic nature of this parameter enables the development of a stochastic optimization method that can determine optimal channel geometries for controlled capillary rise.

Chemically reacting flows through porous media are widespread in biological, environmental, and engineering applications. Yet, understanding these flows remains an outstanding challenging. This letter reveals that hydrodynamic dispersion affects reaction fronts in ways analogous to free turbulence. Our findings thus point to a regime diagram that elucidates the pore-scale coupling between fundamental processes, offering valuable theoretical insights into these complex flows.

In this work, additively manufactured (AM) aluminum nitride (AlN) ceramic heat pipes were developed to improve spacecraft heat rejection capabilities beyond the current state-of-the-art metal systems. A low sintering temperature aluminum nitride slurry is developed for digital light processing printing (DLP) and the optimal debinding curves are examined. Printed AlN parts are characterized via SEM and optical profilometry. AlN 3D-printed parts are also tested for compatibility with aluminum bromide, aluminum chloride, and iodine, among other proposed working fluids at 350-600 K in an inert atmosphere, with reactivity measured via SEM and Fourier transform infrared spectroscopy (FTIR).

Additively manufactured porous ceramic electrospray emitters developed with microscale 3-D printing have shown potential to operate similarly to electrospray emitters fabricated via subtractive manufacturing methods. However, the emission behavior of additively manufactured emitters requires further characterization. In this work, we develop a porous ceramic emitter via two-photon polymerization and characterize its emission performance with 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) using direct current-applied voltage measurements and time-of-flight mass spectrometry. 3-D geometrical characterization of the emitters is performed via scanning electron microscope and laser scanning confocal microscope imaging.

Insects perform feats of strength and endurance that belie their small stature. Insect-scale robots-although subject to the same scaling laws-demonstrate reduced performance because existing microactuator technologies are driven by low-energy density power sources and produce small forces and/or displacements. The use of high-energy density chemical fuels to power small, soft actuators represents a possible solution. We demonstrate a 325-milligram soft combustion microactuator that can achieve displacements of 140%, operate at frequencies >100 hertz, and generate forces >9.5 newtons. With these actuators, we powered an insect-scale quadrupedal robot, which demonstrated a variety of gait patterns, directional control, and a payload capacity 22 times its body weight. These features enabled locomotion through uneven terrain and over obstacles.

View Video Presentation: https://doi.org/10.2514/6.2023-0315.vid As the frequency of SmallSat launches continues to increase, technology solutions to enable fast, accurate, and scalable manufacturing of parts are necessary to meet the demand. In this work, additively manufactured technical ceramics are examined to meet the needs of spacecraft propulsion systems, specifically thrust chambers for use with monopropellants. This research focuses on Digital Light Processing (DLP), a lithography-based AM technique for ceramics that involves exposing a photosensitive liquid polymer resin containing a suspension of ceramic particles to UV light layer-by-layer. This work investigates non-oxide ceramics which have exceptional thermal shock resistance and mechanical strength which can improve the operational lifespan of printed thrust chambers. Commercially available oxide ceramic slurries were first trialed, serving as a baseline for comparison to in-development non-oxide ceramic slurries. Mechanical and thermal testing was performed on printed test articles to determine suitability for aerospace applications.

View Video Presentation: https://doi.org/10.2514/6.2023-0261.vid This work presents a new approach for fabricating porous ceramic emitters using microscale 3D printing for electrospray thrusters and other applications. A method for tuning the ceramic’s permeability through sintering is also presented. Direct current measurements in response to an applied voltage was used to characterize the emission of individual emitters with EMI-BF4. Radiography experiments were performed at a synchrotron facility to image capillary flow inside porous emitters during initial wetting.